write-behind: implement causal ordering and other cleanup

Rules of causal ordering implemented:

- If request A arrives after the acknowledgement (to the app,
  i.e, STACK_UNWIND) of another request B, then request B is
  said to have 'caused' request A.

- (corollary) Two requests, which at any point of time, are
  unacknowledged simultaneously in the system can never 'cause'
  each other (wb_inode->gen is based on this)

- If request A is caused by request B, AND request A's region
  has an overlap with request B's region, then then the fulfillment
  of request A is guaranteed to happen after the fulfillment of B.

- FD of origin is not considered for the determination of causal
  ordering.

- Append operation's region is considered the whole file.

Other cleanup:

- wb_file_t not required any more.

- wb_local_t not required any more.

- O_RDONLY fd's operations now go through the queue to make sure
  writes in the requested region get fulfilled before getting
  processed.

- O_SYNC fd's operations now go through the queue to make sure
  previously acknowledged writes on the file (via other fds) are
  fulfilled before getting processed.

- Option to not honor O_SYNC is now removed.

- Option to ignore O_DIRECT is added (useful when running a VM and the
  drive appears with NCQ/TCQ or WCE=1 for the guest.)

- Option to disable_first_nbytes is removed (as the cause of the
  bug which required this was diagnosed to be missing TCP_NODELAY.)

- General cleanup and better conformance to coding style and convention.

Change-Id: Ib44fb72da3727246b4a85174cb568c2f0231f6de
BUG: 857673
Signed-off-by: Anand Avati <avati@redhat.com>
Reviewed-on: http://review.gluster.org/3947
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Reviewed-by: Amar Tumballi <amarts@redhat.com>

2 files changed, 1070 insertions, 2418 deletions

diff --git a/xlators/mgmt/glusterd/src/glusterd-volgen.c b/xlators/mgmt/glusterd/src/glusterd-volgen.c
index 685470d6..acfe8386 100644
--- a/xlators/mgmt/glusterd/src/glusterd-volgen.c
+++ b/xlators/mgmt/glusterd/src/glusterd-volgen.c
@@ -164,6 +164,8 @@ static struct volopt_map_entry glusterd_volopt_map[] = {
         {"performance.disk-usage-limit",         "performance/quota",         NULL, NULL, NO_DOC, 0},
         {"performance.min-free-disk-limit",      "performance/quota",         NULL, NULL, NO_DOC, 0},
         {"performance.write-behind-window-size", "performance/write-behind",  "cache-size", NULL, DOC},
+        {"performance.strict-o-direct",          "performance/write-behind",  "strict-O_DIRECT", NULL, DOC},
+        {"performance.strict-write-ordering",    "performance/write-behind",  "strict-write-ordering", NULL, DOC},
         {"performance.read-ahead-page-count",    "performance/read-ahead",    "page-count", NULL, DOC},
 
         {"network.frame-timeout",                "protocol/client",           NULL, NULL, NO_DOC, 0},
diff --git a/xlators/performance/write-behind/src/write-behind.c b/xlators/performance/write-behind/src/write-behind.c
index ad1e5f03..53506d94 100644
--- a/xlators/performance/write-behind/src/write-behind.c
+++ b/xlators/performance/write-behind/src/write-behind.c
@@ -8,8 +8,6 @@
   cases as published by the Free Software Foundation.
 */
 
-/*TODO: check for non null wb_file_data before getting wb_file */
-
 
 #ifndef _CONFIG_H
 #define _CONFIG_H
@@ -26,6 +24,7 @@
 #include "common-utils.h"
 #include "call-stub.h"
 #include "statedump.h"
+#include "defaults.h"
 #include "write-behind-mem-types.h"
 
 #define MAX_VECTOR_COUNT          8
@@ -34,96 +33,146 @@
 
 typedef struct list_head list_head_t;
 struct wb_conf;
-struct wb_page;
 struct wb_inode;
 
 typedef struct wb_inode {
-        size_t       window_conf;
-        size_t       window_current;
-        size_t       aggregate_current;
-        int32_t      op_ret;
+        ssize_t      window_conf;
+        ssize_t      window_current;
+	ssize_t      transit; /* size of data stack_wound, and yet
+				 to be fulfilled (wb_fulfill_cbk).
+				 used for trickling_writes
+			      */
+
+        int32_t      op_ret;   /* Last found op_ret and op_errno
+				  while completing a liability
+				  operation. Will be picked by
+				  the next arriving writev/flush/fsync
+			       */
         int32_t      op_errno;
-        list_head_t  request;
-        list_head_t  passive_requests;
+
+        list_head_t  all;    /* All requests, from enqueue() till destroy().
+				Used only for resetting generation
+				number when empty.
+			     */
+        list_head_t  todo;   /* Work to do (i.e, STACK_WIND to server).
+				Once we STACK_WIND, the entry is taken
+				off the list. If it is non-sync write,
+				then we continue to track it via @liability
+				or @temptation depending on the status
+				of its writeback.
+			     */
+        list_head_t  liability;   /* Non-sync writes which are lied
+				     (STACK_UNWIND'ed to caller) but ack
+				     from server not yet complete. This
+				     is the "liability" which we hold, and
+				     must guarantee that dependent operations
+				     which arrive later (which overlap, etc.)
+				     are issued only after their dependencies
+				     in this list are "fulfilled".
+
+				     Server acks for entries in this list
+				     shrinks the window.
+
+				     The sum total of all req->write_size
+				     of entries in this list must be kept less
+				     than the permitted window size.
+				  */
+        list_head_t  temptation;  /* Operations for which we are tempted
+				     to 'lie' (write-behind), but temporarily
+				     holding off (because of insufficient
+				     window capacity, etc.)
+
+				     This is the list to look at to grow
+				     the window (in __wb_pick_unwinds()).
+
+				     Entries typically get chosen from
+				     write-behind from this list, and therefore
+				     get "upgraded" to the "liability" list.
+			     */
+	uint64_t     gen;    /* Liability generation number. Represents
+				the current 'state' of liability. Every
+				new addition to the liability list bumps
+				the generation number.
+
+				a newly arrived request is only required
+				to perform causal checks against the entries
+				in the liability list which were present
+				at the time of its addition. the generation
+				number at the time of its addition is stored
+				in the request and used during checks.
+
+				the liability list can grow while the request
+				waits in the todo list waiting for its
+				dependent operations to complete. however
+				it is not of the request's concern to depend
+				itself on those new entries which arrived
+				after it arrived (i.e, those that have a
+				liability generation higher than itself)
+			     */
         gf_lock_t    lock;
         xlator_t    *this;
-}wb_inode_t;
-
-typedef struct wb_file {
-        int32_t           flags;
-        int               disabled;
-        fd_t             *fd;
-        size_t            disable_till;
-        enum _gf_boolean  dont_wind;
-} wb_file_t;
+} wb_inode_t;
 
 
 typedef struct wb_request {
-        list_head_t           list;
+        list_head_t           all;
+        list_head_t           todo;
+	list_head_t           lie;  /* either in @liability or @temptation */
         list_head_t           winds;
         list_head_t           unwinds;
-        list_head_t           other_requests;
+
         call_stub_t          *stub;
-        size_t                write_size;
+
+        size_t                write_size;  /* currently held size
+					      (after collapsing) */
+	size_t                orig_size;   /* size which arrived with the request.
+					      This is the size by which we grow
+					      the window when unwinding the frame.
+					   */
+        size_t                total_size;  /* valid only in @head in wb_fulfill().
+					      This is the size with which we perform
+					      STACK_WIND to server and therefore the
+					      amount by which we shrink the window.
+					   */
+
+	int                   op_ret;
+	int                   op_errno;
+
         int32_t               refcount;
         wb_inode_t           *wb_inode;
         glusterfs_fop_t       fop;
         gf_lkowner_t          lk_owner;
-        union {
-                struct  {
-                        char  write_behind;
-                        char  stack_wound;
-                        char  got_reply;
-                        char  virgin;
-                        char  flush_all;     /* while trying to sync to back-end,
-                                             * don't wait till a data of size
-                                             * equal to configured aggregate-size
-                                             * is accumulated, instead sync
-                                             * whatever data currently present in
-                                             * request queue.
-                                             */
-
-                }write_request;
-
-                struct {
-                        char marked_for_resume;
-                }other_requests;
-        }flags;
+	struct iobref        *iobref;
+	uint64_t              gen;  /* inode liability state at the time of
+				       request arrival */
+
+	fd_t                 *fd;
+	struct {
+		size_t        size;          /* 0 size == till infinity */
+		off_t         off;
+		int           append:1;      /* offset is invalid. only one
+						outstanding append at a time */
+		int           tempted:1;     /* true only for non-sync writes */
+		int           lied:1;        /* sin committed */
+		int           fulfilled:1;   /* got server acknowledgement */
+		int           go:1;          /* enough aggregating, good to go */
+	} ordering;
 } wb_request_t;
 
-struct wb_conf {
+
+typedef struct wb_conf {
         uint64_t         aggregate_size;
         uint64_t         window_size;
-        uint64_t         disable_till;
-        gf_boolean_t     enable_O_SYNC;
         gf_boolean_t     flush_behind;
-        gf_boolean_t     enable_trickling_writes;
-};
+        gf_boolean_t     trickling_writes;
+	gf_boolean_t     strict_write_ordering;
+	gf_boolean_t     strict_O_DIRECT;
+} wb_conf_t;
 
-typedef struct wb_local {
-        list_head_t     winds;
-        int32_t         flags;
-        fd_t           *fd;
-        wb_request_t   *request;
-        int             op_ret;
-        int             op_errno;
-        call_frame_t   *frame;
-        int32_t         reply_count;
-        wb_inode_t     *wb_inode;
-} wb_local_t;
-
-typedef struct wb_conf wb_conf_t;
-typedef struct wb_page wb_page_t;
 
-int32_t
-wb_process_queue (call_frame_t *frame, wb_inode_t *wb_inode);
-
-ssize_t
-wb_sync (call_frame_t *frame, wb_inode_t *wb_inode, list_head_t *winds);
+void
+wb_process_queue (wb_inode_t *wb_inode);
 
-ssize_t
-__wb_mark_winds (list_head_t *list, list_head_t *winds, size_t aggregate_size,
-                 char enable_trickling_writes);
 
 wb_inode_t *
 __wb_inode_ctx_get (xlator_t *this, inode_t *inode)
@@ -156,37 +205,6 @@ out:
 }
 
 
-wb_file_t *
-__wb_fd_ctx_get (xlator_t *this, fd_t *fd)
-{
-        wb_file_t *wb_file = NULL;
-        uint64_t   value   = 0;
-
-        __fd_ctx_get (fd, this, &value);
-        wb_file = (wb_file_t *)(unsigned long)value;
-
-        return wb_file;
-}
-
-
-wb_file_t *
-wb_fd_ctx_get (xlator_t *this, fd_t *fd)
-{
-        wb_file_t *wb_file = NULL;
-
-        GF_VALIDATE_OR_GOTO ("write-behind", this, out);
-        GF_VALIDATE_OR_GOTO (this->name, fd, out);
-
-        LOCK (&fd->lock);
-        {
-                wb_file = __wb_fd_ctx_get (this, fd);
-        }
-        UNLOCK (&fd->lock);
-
-out:
-        return wb_file;
-}
-
 /*
   Below is a succinct explanation of the code deciding whether two regions
   overlap, from Pavan <tcp@gluster.com>.
@@ -211,19 +229,26 @@ out:
   }
 */
 
-static inline char
-wb_requests_overlap (wb_request_t *request1, wb_request_t *request2)
+gf_boolean_t
+wb_requests_overlap (wb_request_t *req1, wb_request_t *req2)
 {
-        off_t            r1_start   = 0, r1_end = 0, r2_start = 0, r2_end = 0;
+        off_t            r1_start = 0;
+	off_t            r1_end = 0;
+	off_t            r2_start = 0;
+	off_t            r2_end = 0;
         enum _gf_boolean do_overlap = 0;
 
-        r1_start = request1->stub->args.writev.off;
-        r1_end = r1_start + iov_length (request1->stub->args.writev.vector,
-                                        request1->stub->args.writev.count);
+        r1_start = req1->ordering.off;
+	if (req1->ordering.size)
+		r1_end = r1_start + req1->ordering.size - 1;
+	else
+		r1_end = ULLONG_MAX;
 
-        r2_start = request2->stub->args.writev.off;
-        r2_end = r2_start + iov_length (request2->stub->args.writev.vector,
-                                        request2->stub->args.writev.count);
+        r2_start = req2->ordering.off;
+	if (req2->ordering.size)
+		r2_end = r2_start + req2->ordering.size - 1;
+	else
+		r2_end = ULLONG_MAX;
 
         do_overlap = ((r1_end >= r2_start) && (r2_end >= r1_start));
 
@@ -231,72 +256,112 @@ wb_requests_overlap (wb_request_t *request1, wb_request_t *request2)
 }
 
 
-static inline char
-wb_overlap (list_head_t *list, wb_request_t *request)
+gf_boolean_t
+wb_requests_conflict (wb_request_t *lie, wb_request_t *req)
 {
-        char          overlap = 0;
-        wb_request_t *tmp     = NULL;
+	wb_conf_t  *conf = NULL;
 
-        GF_VALIDATE_OR_GOTO ("write-behind", list, out);
-        GF_VALIDATE_OR_GOTO ("write-behind", request, out);
+	conf = req->wb_inode->this->private;
 
-        list_for_each_entry (tmp, list, list) {
-                if (tmp == request) {
-                        break;
-                }
+	if (lie == req)
+		/* request cannot conflict with itself */
+		return _gf_false;
 
-                overlap = wb_requests_overlap (tmp, request);
-                if (overlap) {
-                        break;
-                }
+	if (lie->gen >= req->gen)
+		/* this liability entry was behind
+		   us in the todo list */
+		return _gf_false;
+
+	if (lie->ordering.append)
+		/* all modifications wait for the completion
+		   of outstanding append */
+		return _gf_true;
+
+	if (conf->strict_write_ordering)
+		/* We are sure (lie->gen < req->gen) by now. So
+		   skip overlap check if strict write ordering is
+		   requested and always return "conflict" against a
+		   lower generation lie. */
+		return _gf_true;
+
+	return wb_requests_overlap (lie, req);
+}
+
+
+gf_boolean_t
+wb_liability_has_conflict (wb_inode_t *wb_inode, wb_request_t *req)
+{
+        wb_request_t *each     = NULL;
+
+        list_for_each_entry (each, &wb_inode->liability, lie) {
+		if (wb_requests_conflict (each, req))
+			return _gf_true;
         }
 
-out:
-        return overlap;
+        return _gf_false;
 }
 
 
 static int
-__wb_request_unref (wb_request_t *this)
+__wb_request_unref (wb_request_t *req)
 {
-        int ret = -1;
+        int         ret = -1;
+	wb_inode_t *wb_inode = NULL;
 
-        GF_VALIDATE_OR_GOTO ("write-behind", this, out);
+	wb_inode = req->wb_inode;
 
-        if (this->refcount <= 0) {
+        if (req->refcount <= 0) {
                 gf_log ("wb-request", GF_LOG_WARNING,
-                        "refcount(%d) is <= 0", this->refcount);
+                        "refcount(%d) is <= 0", req->refcount);
                 goto out;
         }
 
-        ret = --this->refcount;
-        if (this->refcount == 0) {
-                list_del_init (&this->list);
-                if (this->stub && this->stub->fop == GF_FOP_WRITE) {
-                        call_stub_destroy (this->stub);
-                }
+        ret = --req->refcount;
+        if (req->refcount == 0) {
+                list_del_init (&req->todo);
+                list_del_init (&req->lie);
 
-                GF_FREE (this);
-        }
+		list_del_init (&req->all);
+		if (list_empty (&wb_inode->all)) {
+			wb_inode->gen = 0;
+			/* in case of accounting errors? */
+			wb_inode->window_current = 0;
+		}
+
+		list_del_init (&req->winds);
+		list_del_init (&req->unwinds);
+
+                if (req->stub && req->ordering.tempted) {
+                        call_stub_destroy (req->stub);
+			req->stub = NULL;
+                } /* else we would have call_resume()'ed */
+
+		if (req->iobref)
+			iobref_unref (req->iobref);
 
+		if (req->fd)
+			fd_unref (req->fd);
+
+                GF_FREE (req);
+        }
 out:
         return ret;
 }
 
 
 static int
-wb_request_unref (wb_request_t *this)
+wb_request_unref (wb_request_t *req)
 {
         wb_inode_t *wb_inode = NULL;
         int         ret      = -1;
 
-        GF_VALIDATE_OR_GOTO ("write-behind", this, out);
+        GF_VALIDATE_OR_GOTO ("write-behind", req, out);
 
-        wb_inode = this->wb_inode;
+        wb_inode = req->wb_inode;
 
         LOCK (&wb_inode->lock);
         {
-                ret = __wb_request_unref (this);
+                ret = __wb_request_unref (req);
         }
         UNLOCK (&wb_inode->lock);
 
@@ -306,117 +371,155 @@ out:
 
 
 static wb_request_t *
-__wb_request_ref (wb_request_t *this)
+__wb_request_ref (wb_request_t *req)
 {
-        GF_VALIDATE_OR_GOTO ("write-behind", this, out);
+        GF_VALIDATE_OR_GOTO ("write-behind", req, out);
 
-        if (this->refcount < 0) {
+        if (req->refcount < 0) {
                 gf_log ("wb-request", GF_LOG_WARNING,
-                        "refcount(%d) is < 0", this->refcount);
-                this = NULL;
+                        "refcount(%d) is < 0", req->refcount);
+                req = NULL;
                 goto out;
         }
 
-        this->refcount++;
+        req->refcount++;
 
 out:
-        return this;
+        return req;
 }
 
 
 wb_request_t *
-wb_request_ref (wb_request_t *this)
+wb_request_ref (wb_request_t *req)
 {
         wb_inode_t *wb_inode = NULL;
 
-        GF_VALIDATE_OR_GOTO ("write-behind", this, out);
+        GF_VALIDATE_OR_GOTO ("write-behind", req, out);
 
-        wb_inode = this->wb_inode;
+        wb_inode = req->wb_inode;
         LOCK (&wb_inode->lock);
         {
-                this = __wb_request_ref (this);
+                req = __wb_request_ref (req);
         }
         UNLOCK (&wb_inode->lock);
 
 out:
-        return this;
+        return req;
 }
 
 
-wb_request_t *
-wb_enqueue (wb_inode_t *wb_inode, call_stub_t *stub)
+gf_boolean_t
+wb_enqueue_common (wb_inode_t *wb_inode, call_stub_t *stub, int tempted)
 {
-        wb_request_t *request = NULL, *tmp = NULL;
-        call_frame_t *frame   = NULL;
-        wb_local_t   *local   = NULL;
-        struct iovec *vector  = NULL;
-        int32_t       count   = 0;
+        wb_request_t *req     = NULL;
 
         GF_VALIDATE_OR_GOTO ("write-behind", wb_inode, out);
         GF_VALIDATE_OR_GOTO (wb_inode->this->name, stub, out);
 
-        request = GF_CALLOC (1, sizeof (*request), gf_wb_mt_wb_request_t);
-        if (request == NULL) {
+        req = GF_CALLOC (1, sizeof (*req), gf_wb_mt_wb_request_t);
+        if (!req)
                 goto out;
-        }
 
-        INIT_LIST_HEAD (&request->list);
-        INIT_LIST_HEAD (&request->winds);
-        INIT_LIST_HEAD (&request->unwinds);
-        INIT_LIST_HEAD (&request->other_requests);
+        INIT_LIST_HEAD (&req->all);
+        INIT_LIST_HEAD (&req->todo);
+        INIT_LIST_HEAD (&req->lie);
+        INIT_LIST_HEAD (&req->winds);
+        INIT_LIST_HEAD (&req->unwinds);
 
-        request->stub = stub;
-        request->wb_inode = wb_inode;
-        request->fop  = stub->fop;
-
-        frame = stub->frame;
-        local = frame->local;
-        if (local) {
-                local->request = request;
-        }
+        req->stub = stub;
+        req->wb_inode = wb_inode;
+        req->fop  = stub->fop;
+	req->ordering.tempted = tempted;
 
         if (stub->fop == GF_FOP_WRITE) {
-                vector = stub->args.writev.vector;
-                count = stub->args.writev.count;
+                req->write_size = iov_length (stub->args.writev.vector,
+					      stub->args.writev.count);
 
-                request->write_size = iov_length (vector, count);
-                if (local) {
-                        local->op_ret = request->write_size;
-                        local->op_errno = 0;
-                }
+		/* req->write_size can change as we collapse
+		   small writes. But the window needs to grow
+		   only by how much we acknowledge the app. so
+		   copy the original size in orig_size for the
+		   purpose of accounting.
+		*/
+		req->orig_size = req->write_size;
+
+		/* Let's be optimistic that we can
+		   lie about it
+		*/
+		req->op_ret = req->write_size;
+		req->op_errno = 0;
 
-                request->flags.write_request.virgin = 1;
+		if (stub->args.writev.fd->flags & O_APPEND)
+			req->ordering.append = 1;
         }
 
-        request->lk_owner = frame->root->lk_owner;
+        req->lk_owner = stub->frame->root->lk_owner;
+
+	switch (stub->fop) {
+	case GF_FOP_WRITE:
+		req->ordering.off = stub->args.writev.off;
+		req->ordering.size = req->write_size;
+
+		req->fd = fd_ref (stub->args.writev.fd);
+
+		break;
+	case GF_FOP_READ:
+		req->ordering.off = stub->args.readv.off;
+		req->ordering.size = stub->args.readv.size;
+
+		req->fd = fd_ref (stub->args.readv.fd);
+
+		break;
+	case GF_FOP_TRUNCATE:
+		req->ordering.off = stub->args.truncate.off;
+		req->ordering.size = 0; /* till infinity */
+		break;
+	case GF_FOP_FTRUNCATE:
+		req->ordering.off = stub->args.ftruncate.off;
+		req->ordering.size = 0; /* till infinity */
+
+		req->fd = fd_ref (stub->args.ftruncate.fd);
+
+		break;
+	default:
+		break;
+	}
 
         LOCK (&wb_inode->lock);
         {
-                list_add_tail (&request->list, &wb_inode->request);
-                if (stub->fop == GF_FOP_WRITE) {
-                        /* reference for stack winding */
-                        __wb_request_ref (request);
-
-                        /* reference for stack unwinding */
-                        __wb_request_ref (request);
-
-                        wb_inode->aggregate_current += request->write_size;
-                } else {
-                        list_for_each_entry (tmp, &wb_inode->request, list) {
-                                if (tmp->stub && tmp->stub->fop
-                                    == GF_FOP_WRITE) {
-                                        tmp->flags.write_request.flush_all = 1;
-                                }
-                        }
-
-                        /*reference for resuming */
-                        __wb_request_ref (request);
-                }
+                list_add_tail (&req->all, &wb_inode->all);
+
+		req->gen = wb_inode->gen;
+
+                list_add_tail (&req->todo, &wb_inode->todo);
+		__wb_request_ref (req); /* for wind */
+
+		if (req->ordering.tempted) {
+			list_add_tail (&req->lie, &wb_inode->temptation);
+			__wb_request_ref (req); /* for unwind */
+		}
         }
         UNLOCK (&wb_inode->lock);
 
 out:
-        return request;
+	if (!req)
+		return _gf_false;
+
+	return _gf_true;
+}
+
+
+gf_boolean_t
+wb_enqueue (wb_inode_t *wb_inode, call_stub_t *stub)
+{
+	return wb_enqueue_common (wb_inode, stub, 0);
+}
+
+
+gf_boolean_t
+wb_enqueue_tempted (wb_inode_t *wb_inode, call_stub_t *stub)
+{
+	return wb_enqueue_common (wb_inode, stub, 1);
 }
 
 
@@ -426,18 +529,18 @@ __wb_inode_create (xlator_t *this, inode_t *inode)
         wb_inode_t *wb_inode = NULL;
         wb_conf_t  *conf     = NULL;
 
-        GF_VALIDATE_OR_GOTO ("write-behind", this, out);
         GF_VALIDATE_OR_GOTO (this->name, inode, out);
 
         conf = this->private;
 
         wb_inode = GF_CALLOC (1, sizeof (*wb_inode), gf_wb_mt_wb_inode_t);
-        if (wb_inode == NULL) {
+        if (!wb_inode)
                 goto out;
-        }
 
-        INIT_LIST_HEAD (&wb_inode->request);
-        INIT_LIST_HEAD (&wb_inode->passive_requests);
+        INIT_LIST_HEAD (&wb_inode->all);
+        INIT_LIST_HEAD (&wb_inode->todo);
+        INIT_LIST_HEAD (&wb_inode->liability);
+        INIT_LIST_HEAD (&wb_inode->temptation);
 
         wb_inode->this = this;
 
@@ -452,58 +555,18 @@ out:
 }
 
 
-wb_file_t *
-wb_file_create (xlator_t *this, fd_t *fd, int32_t flags)
-{
-        wb_file_t *file = NULL;
-        wb_conf_t *conf = NULL;
-
-        GF_VALIDATE_OR_GOTO ("write-behind", this, out);
-        GF_VALIDATE_OR_GOTO (this->name, fd, out);
-
-        conf = this->private;
-
-        file = GF_CALLOC (1, sizeof (*file), gf_wb_mt_wb_file_t);
-        if (file == NULL) {
-                goto out;
-        }
-
-        /*
-          fd_ref() not required, file should never decide the existence of
-          an fd
-        */
-        file->fd= fd;
-        /* If O_DIRECT then, we disable chaching */
-        if (((flags & O_DIRECT) == O_DIRECT)
-            || ((flags & O_ACCMODE) == O_RDONLY)
-            || (((flags & O_SYNC) == O_SYNC)
-                && conf->enable_O_SYNC == _gf_true)) {
-                file->disabled = 1;
-        }
-
-        file->flags = flags;
-
-        fd_ctx_set (fd, this, (uint64_t)(unsigned long)file);
-
-out:
-        return file;
-}
-
-
 wb_inode_t *
 wb_inode_create (xlator_t *this, inode_t *inode)
 {
         wb_inode_t *wb_inode = NULL;
 
-        GF_VALIDATE_OR_GOTO ("write-behind", this, out);
         GF_VALIDATE_OR_GOTO (this->name, inode, out);
 
         LOCK (&inode->lock);
         {
                 wb_inode = __wb_inode_ctx_get (this, inode);
-                if (wb_inode == NULL) {
+                if (!wb_inode)
                         wb_inode = __wb_inode_create (this, inode);
-                }
         }
         UNLOCK (&inode->lock);
 
@@ -524,2390 +587,1049 @@ out:
 }
 
 
-int32_t
-wb_lookup_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
-               int32_t op_ret, int32_t op_errno, inode_t *inode,
-               struct iatt *buf, dict_t *dict, struct iatt *postparent)
+void
+__wb_fulfill_request (wb_request_t *req)
 {
-        wb_inode_t *wb_inode = NULL;
+	wb_inode_t *wb_inode = NULL;
 
-        if (op_ret < 0) {
-                goto unwind;
-        }
+	wb_inode = req->wb_inode;
 
-        wb_inode = wb_inode_create (this, inode);
-        if (wb_inode == NULL) {
-                op_ret = -1;
-                op_errno = ENOMEM;
-        }
+	req->ordering.fulfilled = 1;
+	wb_inode->window_current -= req->total_size;
+	wb_inode->transit -= req->total_size;
 
-unwind:
-        STACK_UNWIND_STRICT (lookup, frame, op_ret, op_errno, inode, buf,
-                             dict, postparent);
+	if (!req->ordering.lied) {
+		/* TODO: fail the req->frame with error if
+		   necessary
+		*/
+	}
 
-        return 0;
+	__wb_request_unref (req);
 }
 
 
-int32_t
-wb_lookup (call_frame_t *frame, xlator_t *this, loc_t *loc,
-           dict_t *xdata)
+void
+wb_head_done (wb_request_t *head)
 {
-        STACK_WIND (frame, wb_lookup_cbk, FIRST_CHILD(this),
-                    FIRST_CHILD(this)->fops->lookup, loc, xdata);
-        return 0;
-}
-
+	wb_request_t *req = NULL;
+	wb_request_t *tmp     = NULL;
+	wb_inode_t   *wb_inode = NULL;
 
-int32_t
-wb_sync_cbk (call_frame_t *frame, void *cookie, xlator_t *this, int32_t op_ret,
-             int32_t op_errno, struct iatt *prebuf, struct iatt *postbuf,
-             dict_t *xdata)
-{
-        wb_local_t   *local             = NULL;
-        list_head_t  *winds             = NULL;
-        wb_inode_t   *wb_inode          = NULL;
-        wb_request_t *request           = NULL, *dummy = NULL;
-        wb_local_t   *per_request_local = NULL;
-        int32_t       ret               = -1;
-	int32_t	      total_write_size	= 0;
-        fd_t         *fd                = NULL;
+	wb_inode = head->wb_inode;
 
-        GF_ASSERT (frame);
-        GF_ASSERT (this);
+	LOCK (&wb_inode->lock);
+	{
+		list_for_each_entry_safe (req, tmp, &head->winds, winds) {
+			__wb_fulfill_request (req);
+		}
+		__wb_fulfill_request (head);
+	}
+	UNLOCK (&wb_inode->lock);
+}
 
-        local = frame->local;
-        winds = &local->winds;
 
-        fd = local->fd;
+void
+wb_inode_err (wb_inode_t *wb_inode, int op_errno)
+{
+	LOCK (&wb_inode->lock);
+	{
+		wb_inode->op_ret = -1;
+		wb_inode->op_errno = op_errno;
+	}
+	UNLOCK (&wb_inode->lock);
+}
 
-        wb_inode = wb_inode_ctx_get (this, fd->inode);
-        GF_VALIDATE_OR_GOTO (this->name, wb_inode, out);
 
-        LOCK (&wb_inode->lock);
-        {
-                list_for_each_entry_safe (request, dummy, winds, winds) {
-                        request->flags.write_request.got_reply = 1;
-
-                        if (!request->flags.write_request.write_behind
-                            && (op_ret == -1)) {
-                                per_request_local = request->stub->frame->local;
-                                per_request_local->op_ret = op_ret;
-                                per_request_local->op_errno = op_errno;
-                        }
-
-                        if (request->flags.write_request.write_behind) {
-                                wb_inode->window_current -= request->write_size;
-				total_write_size += request->write_size;
-                        }
-
-                        __wb_request_unref (request);
-                }
+int
+wb_fulfill_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
+		int32_t op_ret, int32_t op_errno, struct iatt *prebuf,
+		struct iatt *postbuf, dict_t *xdata)
+{
+        wb_inode_t   *wb_inode   = NULL;
+        wb_request_t *head       = NULL;
 
-                if (op_ret == -1) {
-                        wb_inode->op_ret = op_ret;
-                        wb_inode->op_errno = op_errno;
-		} else if (op_ret < total_write_size) {
-			/*
-			 * We've encountered a short write, for whatever reason.
-			 * Set an EIO error for the next fop. This should be
-			 * valid for writev or flush (close).
-			 *
-			 * TODO: Retry the write so we can potentially capture
-			 * a real error condition (i.e., ENOSPC).
-			 */
-			wb_inode->op_ret = -1;
-			wb_inode->op_errno = EIO;
-		}
-        }
-        UNLOCK (&wb_inode->lock);
+	head = frame->local;
+	frame->local = NULL;
 
-        ret = wb_process_queue (frame, wb_inode);
-        if (ret == -1) {
-                if (errno == ENOMEM) {
-                        LOCK (&wb_inode->lock);
-                        {
-                                wb_inode->op_ret = -1;
-                                wb_inode->op_errno = ENOMEM;
-                        }
-                        UNLOCK (&wb_inode->lock);
-                }
+        wb_inode = head->wb_inode;
 
-                gf_log (this->name, GF_LOG_WARNING,
-                        "request queue processing failed");
-        }
+	if (op_ret == -1) {
+		wb_inode_err (wb_inode, op_errno);
+	} else if (op_ret < head->total_size) {
+		/*
+		 * We've encountered a short write, for whatever reason.
+		 * Set an EIO error for the next fop. This should be
+		 * valid for writev or flush (close).
+		 *
+		 * TODO: Retry the write so we can potentially capture
+		 * a real error condition (i.e., ENOSPC).
+		 */
+		wb_inode_err (wb_inode, EIO);
+	}
 
-        /* safe place to do fd_unref */
-        fd_unref (fd);
+	wb_head_done (head);
 
-        frame->local = NULL;
-
-        if (local != NULL) {
-                mem_put (frame->local);
-        }
+        wb_process_queue (wb_inode);
 
         STACK_DESTROY (frame->root);
 
-out:
         return 0;
 }
 
 
-ssize_t
-wb_sync (call_frame_t *frame, wb_inode_t *wb_inode, list_head_t *winds)
-{
-        wb_request_t  *dummy                = NULL, *request = NULL;
-        wb_request_t  *first_request        = NULL, *next = NULL;
-        size_t         total_count          = 0, count = 0;
-        size_t         copied               = 0;
-        call_frame_t  *sync_frame           = NULL;
-        struct iobref *iobref               = NULL;
-        wb_local_t    *local                = NULL;
-        struct iovec  *vector               = NULL;
-        ssize_t        current_size         = 0, bytes = 0;
-        size_t         bytecount            = 0;
-        wb_conf_t     *conf                 = NULL;
-        fd_t          *fd                   = NULL;
-        int32_t        op_errno             = -1;
-        off_t          next_offset_expected = 0;
-        gf_lkowner_t   lk_owner             = {0, };
-
-        GF_VALIDATE_OR_GOTO_WITH_ERROR ((wb_inode ? wb_inode->this->name
-                                         : "write-behind"), frame,
-                                        out, bytes, -1);
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (frame->this->name, wb_inode, out, bytes,
-                                        -1);
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (frame->this->name, winds, out, bytes,
-                                        -1);
-
-        conf = wb_inode->this->private;
-        list_for_each_entry (request, winds, winds) {
-                total_count += request->stub->args.writev.count;
-                if (total_count > 0) {
-                        break;
-                }
-        }
+#define WB_IOV_LOAD(vec, cnt, req, head) do {				\
+		memcpy (&vec[cnt], req->stub->args.writev.vector,	\
+			(req->stub->args.writev.count * sizeof(vec[0]))); \
+		cnt += req->stub->args.writev.count;			\
+		head->total_size += req->write_size;			\
+	} while (0)
 
-        if (total_count == 0) {
-                gf_log (wb_inode->this->name, GF_LOG_TRACE,
-                        "no vectors are to be synced");
-                goto out;
-        }
 
-        list_for_each_entry_safe (request, dummy, winds, winds) {
-                if (!vector) {
-                        vector = GF_MALLOC (VECTORSIZE (MAX_VECTOR_COUNT),
-                                            gf_wb_mt_iovec);
-                        if (vector == NULL) {
-                                bytes = -1;
-                                op_errno = ENOMEM;
-                                goto out;
-                        }
-
-                        iobref = iobref_new ();
-                        if (iobref == NULL) {
-                                bytes = -1;
-                                op_errno = ENOMEM;
-                                goto out;
-                        }
-
-                        local = mem_get0 (THIS->local_pool);
-                        if (local == NULL) {
-                                bytes = -1;
-                                op_errno = ENOMEM;
-                                goto out;
-                        }
-
-                        INIT_LIST_HEAD (&local->winds);
-
-                        first_request = request;
-                        current_size = 0;
-
-                        next_offset_expected = request->stub->args.writev.off
-                                + request->write_size;
-                        lk_owner = request->lk_owner;
-                }
+void
+wb_fulfill_head (wb_inode_t *wb_inode, wb_request_t *head)
+{
+	struct iovec   vector[MAX_VECTOR_COUNT];
+	int            count = 0;
+	wb_request_t  *req = NULL;
+	call_frame_t  *frame = NULL;
 
-                count += request->stub->args.writev.count;
-                bytecount = VECTORSIZE (request->stub->args.writev.count);
-                memcpy (((char *)vector)+copied,
-                        request->stub->args.writev.vector,
-                        bytecount);
-                copied += bytecount;
+	frame = create_frame (wb_inode->this, wb_inode->this->ctx->pool);
+	if (!frame)
+		goto enomem;
 
-                current_size += request->write_size;
+	WB_IOV_LOAD (vector, count, head, head);
 
-                if (request->stub->args.writev.iobref) {
-                        iobref_merge (iobref,
-                                      request->stub->args.writev.iobref);
-                }
+	list_for_each_entry (req, &head->winds, winds) {
+		WB_IOV_LOAD (vector, count, req, head);
 
-                next = NULL;
-                if (request->winds.next != winds) {
-                        next = list_entry (request->winds.next,
-                                           wb_request_t, winds);
-                }
+		iobref_merge (head->stub->args.writev.iobref,
+			      req->stub->args.writev.iobref);
+	}
 
-                list_del_init (&request->winds);
-                list_add_tail (&request->winds, &local->winds);
-
-                if ((!next)
-                    || ((count + next->stub->args.writev.count)
-                        > MAX_VECTOR_COUNT)
-                    || ((current_size + next->write_size)
-                        > conf->aggregate_size)
-                    || (next_offset_expected != next->stub->args.writev.off)
-                    || (!is_same_lkowner (&lk_owner, &next->lk_owner))
-                    || (request->stub->args.writev.fd
-                        != next->stub->args.writev.fd)) {
-
-                        sync_frame = copy_frame (frame);
-                        if (sync_frame == NULL) {
-                                bytes = -1;
-                                op_errno = ENOMEM;
-                                goto out;
-                        }
-
-                        frame->root->lk_owner = lk_owner;
-
-                        local->wb_inode = wb_inode;
-                        sync_frame->local = local;
-
-                        local->fd = fd = fd_ref (request->stub->args.writev.fd);
-
-                        bytes += current_size;
-                        STACK_WIND (sync_frame, wb_sync_cbk,
-                                    FIRST_CHILD(sync_frame->this),
-                                    FIRST_CHILD(sync_frame->this)->fops->writev,
-                                    fd, vector, count,
-                                    first_request->stub->args.writev.off,
-                                    first_request->stub->args.writev.flags,
-                                    iobref, NULL);
+	frame->root->lk_owner = head->lk_owner;
+	frame->local = head;
 
-                        iobref_unref (iobref);
-                        GF_FREE (vector);
-                        first_request = NULL;
-                        iobref = NULL;
-                        vector = NULL;
-                        sync_frame = NULL;
-                        local = NULL;
-                        copied = count = 0;
-                }
-        }
+	LOCK (&wb_inode->lock);
+	{
+		wb_inode->transit += head->total_size;
+	}
+	UNLOCK (&wb_inode->lock);
 
-out:
-        if (sync_frame != NULL) {
-                sync_frame->local = NULL;
-                STACK_DESTROY (sync_frame->root);
-        }
+	STACK_WIND (frame, wb_fulfill_cbk, FIRST_CHILD (frame->this),
+		    FIRST_CHILD (frame->this)->fops->writev,
+		    head->fd, vector, count,
+		    head->stub->args.writev.off,
+		    head->stub->args.writev.flags,
+		    head->stub->args.writev.iobref, NULL);
 
-        if (local != NULL) {
-                /* had we winded these requests, we would have unrefed
-                 * in wb_sync_cbk.
-                 */
-                list_for_each_entry_safe (request, dummy, &local->winds,
-                                          winds) {
-                        wb_request_unref (request);
-                }
+	return;
+enomem:
+	wb_inode_err (wb_inode, ENOMEM);
 
-                mem_put (local);
-                local = NULL;
-        }
+	wb_head_done (head);
 
-        if (iobref != NULL) {
-                iobref_unref (iobref);
-        }
+	return;
+}
 
-        GF_FREE (vector);
-
-        if (bytes == -1) {
-                /*
-                 * had we winded these requests, we would have unrefed
-                 * in wb_sync_cbk.
-                 */
-                if (local) {
-                        list_for_each_entry_safe (request, dummy, &local->winds,
-                                                  winds) {
-                                wb_request_unref (request);
-                        }
-                }
 
-                if (wb_inode != NULL) {
-                        LOCK (&wb_inode->lock);
-                        {
-                                wb_inode->op_ret = -1;
-                                wb_inode->op_errno = op_errno;
-                        }
-                        UNLOCK (&wb_inode->lock);
-                }
-        }
-
-        return bytes;
-}
+#define NEXT_HEAD(head, req) do {					\
+		if (head)						\
+			wb_fulfill_head (wb_inode, head);		\
+		head = req;						\
+		expected_offset = req->stub->args.writev.off +		\
+			req->write_size;				\
+		curr_aggregate = 0;					\
+		vector_count = 0;					\
+	} while (0)
 
 
-int32_t
-wb_stat_cbk (call_frame_t *frame, void *cookie, xlator_t *this, int32_t op_ret,
-             int32_t op_errno, struct iatt *buf, dict_t *xdata)
+void
+wb_fulfill (wb_inode_t *wb_inode, list_head_t *liabilities)
 {
-        wb_local_t   *local         = NULL;
-        wb_request_t *request       = NULL;
-        call_frame_t *process_frame = NULL;
-        wb_inode_t   *wb_inode      = NULL;
-        int32_t       ret           = -1;
-
-        GF_ASSERT (frame);
-        GF_ASSERT (this);
+	wb_request_t  *req     = NULL;
+	wb_request_t  *head    = NULL;
+	wb_request_t  *tmp     = NULL;
+	wb_conf_t     *conf    = NULL;
+	off_t          expected_offset = 0;
+	size_t         curr_aggregate = 0;
+	size_t         vector_count = 0;
 
-        local = frame->local;
-        wb_inode = local->wb_inode;
+	conf = wb_inode->this->private;
 
-        request = local->request;
-        if (request) {
-                process_frame = copy_frame (frame);
-                if (process_frame == NULL) {
-                        op_ret = -1;
-                        op_errno = ENOMEM;
-                }
-        }
+	list_for_each_entry_safe (req, tmp, liabilities, winds) {
+		list_del_init (&req->winds);
 
-        STACK_UNWIND_STRICT (stat, frame, op_ret, op_errno, buf, xdata);
+		if (!head) {
+			NEXT_HEAD (head, req);
+			continue;
+		}
 
-        if (request != NULL) {
-                wb_request_unref (request);
-        }
+		if (req->fd != head->fd) {
+			NEXT_HEAD (head, req);
+			continue;
+		}
 
-        if (process_frame != NULL) {
-                ret = wb_process_queue (process_frame, wb_inode);
-                if (ret == -1) {
-                        if ((errno == ENOMEM) && (wb_inode != NULL)) {
-                                LOCK (&wb_inode->lock);
-                                {
-                                        wb_inode->op_ret = -1;
-                                        wb_inode->op_errno = ENOMEM;
-                                }
-                                UNLOCK (&wb_inode->lock);
-                        }
-
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
+		if (!is_same_lkowner (&req->lk_owner, &head->lk_owner)) {
+			NEXT_HEAD (head, req);
+			continue;
+		}
 
-                STACK_DESTROY (process_frame->root);
-        }
+		if (expected_offset != req->stub->args.writev.off) {
+			NEXT_HEAD (head, req);
+			continue;
+		}
 
-        return 0;
-}
+		if ((curr_aggregate + req->write_size) > conf->aggregate_size) {
+			NEXT_HEAD (head, req);
+			continue;
+		}
 
+		if (vector_count + req->stub->args.writev.count >
+		    MAX_VECTOR_COUNT) {
+			NEXT_HEAD (head, req);
+			continue;
+		}
 
-static int32_t
-wb_stat_helper (call_frame_t *frame, xlator_t *this, loc_t *loc, dict_t *xdata)
-{
-        GF_ASSERT (frame);
-        GF_ASSERT (this);
+		list_add_tail (&req->winds, &head->winds);
+		curr_aggregate += req->write_size;
+		vector_count += req->stub->args.writev.count;
+	}
 
-        STACK_WIND (frame, wb_stat_cbk, FIRST_CHILD(this),
-                    FIRST_CHILD(this)->fops->stat, loc, xdata);
-        return 0;
+	if (head)
+		wb_fulfill_head (wb_inode, head);
+	return;
 }
 
 
-int32_t
-wb_stat (call_frame_t *frame, xlator_t *this, loc_t *loc, dict_t *xdata)
+void
+wb_do_unwinds (wb_inode_t *wb_inode, list_head_t *lies)
 {
-        wb_inode_t   *wb_inode     = NULL;
-        wb_local_t   *local        = NULL;
-        call_stub_t  *stub         = NULL;
-        wb_request_t *request      = NULL;
-        int32_t       ret          = -1, op_errno = EINVAL;
-
-        GF_ASSERT (frame);
-        GF_VALIDATE_OR_GOTO (frame->this->name, this, unwind);
-        GF_VALIDATE_OR_GOTO (frame->this->name, loc, unwind);
-
-        if (loc->inode) {
-                wb_inode = wb_inode_ctx_get (this, loc->inode);
-        }
-
-        local = mem_get0 (this->local_pool);
-        if (local == NULL) {
-                op_errno = ENOMEM;
-                goto unwind;
-        }
-
-        local->wb_inode = wb_inode;
-
-        frame->local = local;
-
-        if (wb_inode) {
-                stub = fop_stat_stub (frame, wb_stat_helper, loc, xdata);
-                if (stub == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
-
-                request = wb_enqueue (wb_inode, stub);
-                if (request == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
+	wb_request_t *req = NULL;
+	wb_request_t *tmp = NULL;
+	call_frame_t *frame = NULL;
+	struct iatt   buf = {0, };
 
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-        } else {
-                STACK_WIND (frame, wb_stat_cbk, FIRST_CHILD(this),
-                            FIRST_CHILD(this)->fops->stat, loc, xdata);
-        }
+        list_for_each_entry_safe (req, tmp, lies, unwinds) {
+                frame = req->stub->frame;
 
-        return 0;
-unwind:
-        STACK_UNWIND_STRICT (stat, frame, -1, op_errno, NULL, NULL);
+                STACK_UNWIND_STRICT (writev, frame, req->op_ret, req->op_errno,
+				     &buf, &buf, NULL); /* :O */
+		req->stub->frame = NULL;
 
-        if (stub) {
-                call_stub_destroy (stub);
+		list_del_init (&req->unwinds);
+                wb_request_unref (req);
         }
 
-        return 0;
+        return;
 }
 
 
-int32_t
-wb_fstat_cbk (call_frame_t *frame, void *cookie, xlator_t *this, int32_t op_ret,
-              int32_t op_errno, struct iatt *buf, dict_t *xdata)
+void
+__wb_pick_unwinds (wb_inode_t *wb_inode, list_head_t *lies)
 {
-        wb_local_t   *local    = NULL;
-        wb_request_t *request  = NULL;
-        wb_inode_t   *wb_inode = NULL;
-        int32_t       ret      = -1;
-
-        GF_ASSERT (frame);
-
-        local = frame->local;
-        wb_inode = local->wb_inode;
-
-        request = local->request;
-        if ((wb_inode != NULL) && (request != NULL)) {
-                wb_request_unref (request);
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        if (errno == ENOMEM) {
-                                op_ret = -1;
-                                op_errno = ENOMEM;
-                        }
-
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-        }
-
-        STACK_UNWIND_STRICT (fstat, frame, op_ret, op_errno, buf, xdata);
-
-        return 0;
-}
+        wb_request_t *req = NULL;
+        wb_request_t *tmp = NULL;
 
+	list_for_each_entry_safe (req, tmp, &wb_inode->temptation, lie) {
+		if (!req->ordering.fulfilled &&
+		    wb_inode->window_current > wb_inode->window_conf)
+			continue;
 
-int32_t
-wb_fstat_helper (call_frame_t *frame, xlator_t *this, fd_t *fd, dict_t *xdata)
-{
-        GF_ASSERT (frame);
-        GF_ASSERT (this);
-
-        STACK_WIND (frame, wb_fstat_cbk, FIRST_CHILD(this),
-                    FIRST_CHILD(this)->fops->fstat, fd, xdata);
-        return 0;
-}
+		list_del_init (&req->lie);
+		list_move_tail (&req->unwinds, lies);
 
+		wb_inode->window_current += req->orig_size;
 
-int32_t
-wb_fstat (call_frame_t *frame, xlator_t *this, fd_t *fd, dict_t *xdata)
-{
-        wb_inode_t   *wb_inode     = NULL;
-        wb_local_t   *local        = NULL;
-        call_stub_t  *stub         = NULL;
-        wb_request_t *request      = NULL;
-        int32_t       ret          = -1;
-        int           op_errno     = EINVAL;
+		if (!req->ordering.fulfilled) {
+			/* burden increased */
+			list_add_tail (&req->lie, &wb_inode->liability);
 
-        GF_ASSERT (frame);
-        GF_VALIDATE_OR_GOTO (frame->this->name, this, unwind);
-        GF_VALIDATE_OR_GOTO (frame->this->name, fd, unwind);
+			req->ordering.lied = 1;
 
-        wb_inode = wb_inode_ctx_get (this, fd->inode);
-        if ((!IA_ISDIR (fd->inode->ia_type)) && (wb_inode == NULL)) {
-                gf_log (this->name, GF_LOG_WARNING,
-                        "wb_inode not found for fd %p", fd);
-                op_errno = EBADFD;
-                goto unwind;
-        }
+			wb_inode->gen++;
+		}
+	}
 
-        local = mem_get0 (this->local_pool);
-        if (local == NULL) {
-                op_errno = ENOMEM;
-                goto unwind;
-        }
+        return;
+}
 
-        local->wb_inode = wb_inode;
 
-        frame->local = local;
+int
+__wb_collapse_small_writes (wb_request_t *holder, wb_request_t *req)
+{
+        char          *ptr    = NULL;
+        struct iobuf  *iobuf  = NULL;
+        struct iobref *iobref = NULL;
+        int            ret    = -1;
 
-        if (wb_inode) {
-                stub = fop_fstat_stub (frame, wb_fstat_helper, fd, xdata);
-                if (stub == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
+        if (!holder->iobref) {
+                /* TODO: check the required size */
+                iobuf = iobuf_get (req->wb_inode->this->ctx->iobuf_pool);
+                if (iobuf == NULL) {
+                        goto out;
                 }
 
-                request = wb_enqueue (wb_inode, stub);
-                if (request == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
+                iobref = iobref_new ();
+                if (iobref == NULL) {
+                        iobuf_unref (iobuf);
+                        goto out;
                 }
 
-                /*
-                  FIXME:should the request queue be emptied in case of error?
-                */
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
+                ret = iobref_add (iobref, iobuf);
+                if (ret != 0) {
+                        iobuf_unref (iobuf);
+                        iobref_unref (iobref);
+                        gf_log (req->wb_inode->this->name, GF_LOG_WARNING,
+                                "cannot add iobuf (%p) into iobref (%p)",
+                                iobuf, iobref);
+                        goto out;
                 }
-        } else {
-                STACK_WIND (frame, wb_fstat_cbk, FIRST_CHILD(this),
-                            FIRST_CHILD(this)->fops->fstat, fd, xdata);
-        }
-
-        return 0;
-
-unwind:
-        STACK_UNWIND_STRICT (fstat, frame, -1, op_errno, NULL, NULL);
-
-        if (stub) {
-                call_stub_destroy (stub);
-        }
 
-        return 0;
-}
-
-
-int32_t
-wb_truncate_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
-                 int32_t op_ret, int32_t op_errno, struct iatt *prebuf,
-                 struct iatt *postbuf, dict_t *xdata)
-{
-        wb_local_t   *local         = NULL;
-        wb_request_t *request       = NULL;
-        wb_inode_t   *wb_inode      = NULL;
-        call_frame_t *process_frame = NULL;
-        int32_t       ret           = -1;
+                iov_unload (iobuf->ptr, holder->stub->args.writev.vector,
+                            holder->stub->args.writev.count);
+                holder->stub->args.writev.vector[0].iov_base = iobuf->ptr;
+		holder->stub->args.writev.count = 1;
 
-        GF_ASSERT (frame);
+                iobref_unref (holder->stub->args.writev.iobref);
+                holder->stub->args.writev.iobref = iobref;
 
-        local = frame->local;
-        wb_inode = local->wb_inode;
-        request = local->request;
+                iobuf_unref (iobuf);
 
-        if ((request != NULL) && (wb_inode != NULL)) {
-                process_frame = copy_frame (frame);
-                if (process_frame == NULL) {
-                        op_ret = -1;
-                        op_errno = ENOMEM;
-                }
+                holder->iobref = iobref_ref (iobref);
         }
 
-        STACK_UNWIND_STRICT (truncate, frame, op_ret, op_errno, prebuf,
-                             postbuf, xdata);
-
-        if (request) {
-                wb_request_unref (request);
-        }
+        ptr = holder->stub->args.writev.vector[0].iov_base + holder->write_size;
 
-        if (process_frame != NULL) {
-                ret = wb_process_queue (process_frame, wb_inode);
-                if (ret == -1) {
-                        if ((errno == ENOMEM) && (wb_inode != NULL)) {
-                                LOCK (&wb_inode->lock);
-                                {
-                                        wb_inode->op_ret = -1;
-                                        wb_inode->op_errno = ENOMEM;
-                                }
-                                UNLOCK (&wb_inode->lock);
-                        }
-
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
+        iov_unload (ptr, req->stub->args.writev.vector,
+                    req->stub->args.writev.count);
 
-                STACK_DESTROY (process_frame->root);
-        }
+        holder->stub->args.writev.vector[0].iov_len += req->write_size;
+        holder->write_size += req->write_size;
+        holder->ordering.size += req->write_size;
 
-        return 0;
+        ret = 0;
+out:
+        return ret;
 }
 
 
-static int32_t
-wb_truncate_helper (call_frame_t *frame, xlator_t *this, loc_t *loc,
-                    off_t offset, dict_t *xdata)
+void
+__wb_preprocess_winds (wb_inode_t *wb_inode)
 {
-        GF_ASSERT (frame);
-        GF_ASSERT (this);
-
-        STACK_WIND (frame, wb_truncate_cbk, FIRST_CHILD(this),
-                    FIRST_CHILD(this)->fops->truncate, loc, offset, xdata);
+        off_t         offset_expected = 0;
+        size_t        space_left      = 0;
+	wb_request_t *req             = NULL;
+	wb_request_t *tmp             = NULL;
+	wb_request_t *holder          = NULL;
+	wb_conf_t    *conf            = NULL;
+        int           ret             = 0;
+	size_t        page_size       = 0;
+
+	/* With asynchronous IO from a VM guest (as a file), there
+	   can be two sequential writes happening in two regions
+	   of the file. But individual (broken down) IO requests
+	   can arrive interleaved.
+
+	   TODO: cycle for each such sequence sifting
+	   through the interleaved ops
+	*/
+
+	page_size = wb_inode->this->ctx->page_size;
+	conf = wb_inode->this->private;
+
+        list_for_each_entry_safe (req, tmp, &wb_inode->todo, todo) {
+		if (!req->ordering.tempted) {
+			if (holder) {
+				if (wb_requests_conflict (holder, req))
+					/* do not hold on write if a
+					   dependent write is in queue */
+					holder->ordering.go = 1;
+			}
+			/* collapse only non-sync writes */
+			continue;
+		} else if (!holder) {
+			/* holder is always a non-sync write */
+			holder = req;
+			continue;
+		}
 
-        return 0;
-}
+		offset_expected = holder->stub->args.writev.off
+			+ holder->write_size;
 
+		if (req->stub->args.writev.off != offset_expected) {
+			holder->ordering.go = 1;
+			holder = req;
+			continue;
+		}
 
-int32_t
-wb_truncate (call_frame_t *frame, xlator_t *this, loc_t *loc, off_t offset,
-             dict_t *xdata)
-{
-        wb_inode_t   *wb_inode     = NULL;
-        wb_local_t   *local        = NULL;
-        call_stub_t  *stub         = NULL;
-        wb_request_t *request      = NULL;
-        int32_t       ret          = -1, op_errno = EINVAL;
+		if (!is_same_lkowner (&req->lk_owner, &holder->lk_owner)) {
+			holder->ordering.go = 1;
+			holder = req;
+			continue;
+		}
 
-        GF_ASSERT (frame);
-        GF_VALIDATE_OR_GOTO (frame->this->name, this, unwind);
-        GF_VALIDATE_OR_GOTO (frame->this->name, loc, unwind);
+		space_left = page_size - holder->write_size;
 
-        if (loc->inode) {
-                wb_inode = wb_inode_ctx_get (this, loc->inode);
-        }
+		if (space_left < req->write_size) {
+			holder->ordering.go = 1;
+			holder = req;
+			continue;
+		}
 
-        local = mem_get0 (this->local_pool);
-        if (local == NULL) {
-                op_errno = ENOMEM;
-                goto unwind;
-        }
+		ret = __wb_collapse_small_writes (holder, req);
+		if (ret)
+			continue;
 
-        local->wb_inode = wb_inode;
+		/* collapsed request is as good as wound
+		   (from its p.o.v)
+		*/
+		list_del_init (&req->todo);
+		__wb_fulfill_request (req);
 
-        frame->local = local;
-        if (wb_inode) {
-                stub = fop_truncate_stub (frame, wb_truncate_helper, loc,
-                                          offset, xdata);
-                if (stub == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
+               /* Only the last @holder in queue which
 
-                request = wb_enqueue (wb_inode, stub);
-                if (request == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
+                  - does not have any non-buffered-writes following it
+                  - has not yet filled its capacity
 
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-        } else {
-                STACK_WIND (frame, wb_truncate_cbk, FIRST_CHILD(this),
-                            FIRST_CHILD(this)->fops->truncate, loc, offset,
-                            xdata);
+                  does not get its 'go' set, in anticipation of the arrival
+                  of consecutive smaller writes.
+               */
         }
 
-        return 0;
-
-unwind:
-        STACK_UNWIND_STRICT (truncate, frame, -1, op_errno, NULL, NULL, NULL);
+	/* but if trickling writes are enabled, then do not hold back
+	   writes if there are no outstanding requests
+	*/
 
-        if (stub) {
-                call_stub_destroy (stub);
-        }
+	if (conf->trickling_writes && !wb_inode->transit && holder)
+		holder->ordering.go = 1;
 
-        return 0;
+        return;
 }
 
 
-int32_t
-wb_ftruncate_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
-                  int32_t op_ret, int32_t op_errno, struct iatt *prebuf,
-                  struct iatt *postbuf, dict_t *xdata)
+void
+__wb_pick_winds (wb_inode_t *wb_inode, list_head_t *tasks,
+		 list_head_t *liabilities)
 {
-        wb_local_t   *local    = NULL;
-        wb_request_t *request  = NULL;
-        wb_inode_t   *wb_inode = NULL;
-        int32_t       ret      = -1;
-
-        GF_ASSERT (frame);
-
-        local = frame->local;
-        wb_inode = local->wb_inode;
-        request = local->request;
-
-        if ((request != NULL) && (wb_inode != NULL)) {
-                wb_request_unref (request);
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        if (errno == ENOMEM) {
-                                op_ret = -1;
-                                op_errno = ENOMEM;
-                        }
-
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-        }
-
-        STACK_UNWIND_STRICT (ftruncate, frame, op_ret, op_errno, prebuf,
-                             postbuf, xdata);
+	wb_request_t *req = NULL;
+	wb_request_t *tmp = NULL;
 
-        return 0;
-}
+	list_for_each_entry_safe (req, tmp, &wb_inode->todo, todo) {
+		if (wb_liability_has_conflict (wb_inode, req))
+			continue;
 
+		if (req->ordering.tempted && !req->ordering.go)
+			/* wait some more */
+			continue;
 
-static int32_t
-wb_ftruncate_helper (call_frame_t *frame, xlator_t *this, fd_t *fd,
-                     off_t offset, dict_t *xdata)
-{
-        GF_ASSERT (frame);
-        GF_ASSERT (this);
+		list_del_init (&req->todo);
 
-        STACK_WIND (frame, wb_ftruncate_cbk, FIRST_CHILD(this),
-                    FIRST_CHILD(this)->fops->ftruncate, fd, offset, xdata);
-        return 0;
+		if (req->ordering.tempted)
+			list_add_tail (&req->winds, liabilities);
+		else
+			list_add_tail (&req->winds, tasks);
+	}
 }
 
 
-int32_t
-wb_ftruncate (call_frame_t *frame, xlator_t *this, fd_t *fd, off_t offset,
-              dict_t *xdata)
+void
+wb_do_winds (wb_inode_t *wb_inode, list_head_t *tasks)
 {
-        wb_inode_t   *wb_inode     = NULL;
-        wb_local_t   *local        = NULL;
-        call_stub_t  *stub         = NULL;
-        wb_request_t *request      = NULL;
-        int32_t       ret          = -1;
-        int           op_errno     = EINVAL;
-
-        GF_ASSERT (frame);
-        GF_VALIDATE_OR_GOTO (frame->this->name, this, unwind);
-        GF_VALIDATE_OR_GOTO (frame->this->name, fd, unwind);
-
-        wb_inode = wb_inode_ctx_get (this, fd->inode);
-        if ((!IA_ISDIR (fd->inode->ia_type)) && (wb_inode == NULL)) {
-                gf_log (this->name, GF_LOG_WARNING,
-                        "wb_inode not found for fd %p", fd);
-                op_errno = EBADFD;
-                goto unwind;
-        }
-
-        local = mem_get0 (this->local_pool);
-        if (local == NULL) {
-                op_errno = ENOMEM;
-                goto unwind;
-        }
-
-        local->wb_inode = wb_inode;
-
-        frame->local = local;
-
-        if (wb_inode) {
-                stub = fop_ftruncate_stub (frame, wb_ftruncate_helper, fd,
-                                           offset, xdata);
-                if (stub == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
-
-                request = wb_enqueue (wb_inode, stub);
-                if (request == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
-
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-        } else {
-                STACK_WIND (frame, wb_ftruncate_cbk, FIRST_CHILD(this),
-                            FIRST_CHILD(this)->fops->ftruncate, fd, offset, xdata);
-        }
-
-        return 0;
+	wb_request_t *req = NULL;
+	wb_request_t *tmp = NULL;
 
-unwind:
-        STACK_UNWIND_STRICT (ftruncate, frame, -1, op_errno, NULL, NULL, NULL);
+	list_for_each_entry_safe (req, tmp, tasks, winds) {
+		list_del_init (&req->winds);
 
-        if (stub) {
-                call_stub_destroy (stub);
-        }
+		call_resume (req->stub);
 
-        return 0;
+		wb_request_unref (req);
+	}
 }
 
 
-int32_t
-wb_setattr_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
-                int32_t op_ret, int32_t op_errno, struct iatt *statpre,
-                struct iatt *statpost, dict_t *xdata)
+void
+wb_process_queue (wb_inode_t *wb_inode)
 {
-        wb_local_t   *local         = NULL;
-        wb_request_t *request       = NULL;
-        call_frame_t *process_frame = NULL;
-        wb_inode_t   *wb_inode      = NULL;
-        int32_t       ret           = -1;
+        list_head_t tasks  = {0, };
+	list_head_t lies = {0, };
+	list_head_t liabilities = {0, };
 
-        GF_ASSERT (frame);
+        INIT_LIST_HEAD (&tasks);
+        INIT_LIST_HEAD (&lies);
+        INIT_LIST_HEAD (&liabilities);
 
-        local = frame->local;
-        wb_inode = local->wb_inode;
-        request = local->request;
+        LOCK (&wb_inode->lock);
+        {
+		__wb_preprocess_winds (wb_inode);
 
-        if (request) {
-                process_frame = copy_frame (frame);
-                if (process_frame == NULL) {
-                        op_ret = -1;
-                        op_errno = ENOMEM;
-                }
-        }
+		__wb_pick_winds (wb_inode, &tasks, &liabilities);
 
-        STACK_UNWIND_STRICT (setattr, frame, op_ret, op_errno, statpre,
-                             statpost, xdata);
+                __wb_pick_unwinds (wb_inode, &lies);
 
-        if (request) {
-                wb_request_unref (request);
         }
+        UNLOCK (&wb_inode->lock);
 
-        if (request && (process_frame != NULL)) {
-                ret = wb_process_queue (process_frame, wb_inode);
-                if (ret == -1) {
-                        if ((errno == ENOMEM) && (wb_inode != NULL)) {
-                                LOCK (&wb_inode->lock);
-                                {
-                                        wb_inode->op_ret = -1;
-                                        wb_inode->op_errno = ENOMEM;
-                                }
-                                UNLOCK (&wb_inode->lock);
-                        }
-
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
+	wb_do_unwinds (wb_inode, &lies);
 
-                STACK_DESTROY (process_frame->root);
-        }
+	wb_do_winds (wb_inode, &tasks);
 
-        return 0;
+	wb_fulfill (wb_inode, &liabilities);
+
+        return;
 }
 
 
-static int32_t
-wb_setattr_helper (call_frame_t *frame, xlator_t *this, loc_t *loc,
-                   struct iatt *stbuf, int32_t valid, dict_t *xdata)
+int
+wb_writev_helper (call_frame_t *frame, xlator_t *this, fd_t *fd,
+		  struct iovec *vector, int32_t count, off_t offset,
+		  uint32_t flags, struct iobref *iobref, dict_t *xdata)
 {
-        GF_ASSERT (frame);
-        GF_ASSERT (this);
-
-        STACK_WIND (frame, wb_setattr_cbk, FIRST_CHILD(this),
-                    FIRST_CHILD(this)->fops->setattr, loc, stbuf, valid, xdata);
-        return 0;
+	STACK_WIND (frame, default_writev_cbk,
+		    FIRST_CHILD (this), FIRST_CHILD (this)->fops->writev,
+		    fd, vector, count, offset, flags, iobref, xdata);
+	return 0;
 }
 
 
-int32_t
-wb_setattr (call_frame_t *frame, xlator_t *this, loc_t *loc,
-            struct iatt *stbuf, int32_t valid, dict_t *xdata)
+int
+wb_writev (call_frame_t *frame, xlator_t *this, fd_t *fd, struct iovec *vector,
+           int32_t count, off_t offset, uint32_t flags, struct iobref *iobref,
+           dict_t *xdata)
 {
-        wb_inode_t   *wb_inode     = NULL;
-        wb_local_t   *local        = NULL;
-        call_stub_t  *stub         = NULL;
-        wb_request_t *request      = NULL;
-        int32_t       ret          = -1, op_errno = EINVAL;
-
-        GF_ASSERT (frame);
-        GF_VALIDATE_OR_GOTO (frame->this->name, this, unwind);
-        GF_VALIDATE_OR_GOTO (frame->this->name, loc, unwind);
+        wb_inode_t   *wb_inode      = NULL;
+	wb_conf_t    *conf          = NULL;
+        gf_boolean_t  wb_disabled   = 0;
+        call_stub_t  *stub          = NULL;
+        int           ret           = -1;
+	int           op_errno      = EINVAL;
+	int           o_direct      = O_DIRECT;
+
+	conf = this->private;
+        wb_inode = wb_inode_create (this, fd->inode);
+	if (!wb_inode) {
+		op_errno = ENOMEM;
+		goto unwind;
+	}
+
+	if (!conf->strict_O_DIRECT)
+		o_direct = 0;
+
+	if (fd->flags & (O_SYNC|O_DSYNC|o_direct))
+		wb_disabled = 1;
+
+	if (flags & (O_SYNC|O_DSYNC|O_DIRECT))
+		/* O_DIRECT flag in params of writev must _always_ be honored */
+		wb_disabled = 1;
+
+	op_errno = 0;
+	LOCK (&wb_inode->lock);
+	{
+		/* pick up a previous error in fulfillment */
+		if (wb_inode->op_ret < 0)
+			op_errno = wb_inode->op_errno;
+
+		wb_inode->op_ret = 0;
+	}
+	UNLOCK (&wb_inode->lock);
+
+        if (op_errno)
+                goto unwind;
 
-        local = mem_get0 (this->local_pool);
-        if (local == NULL) {
+	if (wb_disabled)
+		stub = fop_writev_stub (frame, wb_writev_helper, fd, vector,
+					count, offset, flags, iobref, xdata);
+	else
+		stub = fop_writev_stub (frame, NULL, fd, vector, count, offset,
+					flags, iobref, xdata);
+        if (!stub) {
                 op_errno = ENOMEM;
                 goto unwind;
         }
 
-        frame->local = local;
-
-        if (loc->inode) {
-                wb_inode = wb_inode_ctx_get (this, loc->inode);
-        }
+	if (wb_disabled)
+		ret = wb_enqueue (wb_inode, stub);
+	else
+		ret = wb_enqueue_tempted (wb_inode, stub);
 
-        local->wb_inode = wb_inode;
+	if (!ret) {
+		op_errno = ENOMEM;
+		goto unwind;
+	}
 
-        if (wb_inode) {
-                stub = fop_setattr_stub (frame, wb_setattr_helper, loc, stbuf,
-                                         valid, xdata);
-                if (stub == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
-
-                request = wb_enqueue (wb_inode, stub);
-                if (request == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
-
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-        } else {
-                STACK_WIND (frame, wb_setattr_cbk, FIRST_CHILD(this),
-                            FIRST_CHILD(this)->fops->setattr, loc, stbuf,
-                            valid, xdata);
-        }
+        wb_process_queue (wb_inode);
 
         return 0;
+
 unwind:
-        STACK_UNWIND_STRICT (setattr, frame, -1, op_errno, NULL, NULL, NULL);
+        STACK_UNWIND_STRICT (writev, frame, -1, op_errno, NULL, NULL, NULL);
 
-        if (stub) {
+        if (stub)
                 call_stub_destroy (stub);
-        }
 
         return 0;
 }
 
-void
-wb_disable_all (xlator_t *this, fd_t *origfd)
-{
-        inode_t   *inode   = NULL;
-        fd_t      *otherfd = NULL;
-        wb_file_t *wb_file = NULL;
-
-        inode = origfd->inode;
-
-        LOCK(&inode->lock);
-        {
-                list_for_each_entry (otherfd, &inode->fd_list, inode_list) {
-                        if (otherfd == origfd) {
-                                continue;
-                        }
-
-                        wb_file = wb_fd_ctx_get (this, otherfd);
-                        if (wb_file == NULL) {
-                                continue;
-                        }
-
-                        gf_log(this->name,GF_LOG_DEBUG,
-                               "disabling wb on %p because %p is O_SYNC",
-                               otherfd, origfd);
-                        wb_file->disabled = 1;
-                }
-        }
-        UNLOCK(&inode->lock);
-}
 
-int32_t
-wb_open_cbk (call_frame_t *frame, void *cookie, xlator_t *this, int32_t op_ret,
-             int32_t op_errno, fd_t *fd, dict_t *xdata)
+int
+wb_readv_helper (call_frame_t *frame, xlator_t *this, fd_t *fd, size_t size,
+                 off_t offset, uint32_t flags, dict_t *xdata)
 {
-        int32_t     flags   = 0;
-        wb_file_t  *file    = NULL;
-        wb_local_t *local   = NULL;
-
-        GF_ASSERT (frame);
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (frame->this->name, this, out, op_errno,
-                                        EINVAL);
-        local = frame->local;
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (this->name, local, out, op_errno,
-                                        EINVAL);
-
-        flags = local->flags;
-
-        if (op_ret != -1) {
-                file = wb_file_create (this, fd, flags);
-                if (file == NULL) {
-                        op_ret = -1;
-                        op_errno = ENOMEM;
-                        goto out;
-                }
-        }
-
-out:
-        frame->local = NULL;
-        if (local != NULL) {
-                mem_put (local);
-        }
-
-        STACK_UNWIND_STRICT (open, frame, op_ret, op_errno, fd, xdata);
+        STACK_WIND (frame, default_readv_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->readv, fd, size, offset, flags,
+                    xdata);
         return 0;
 }
 
 
-int32_t
-wb_open (call_frame_t *frame, xlator_t *this, loc_t *loc, int32_t flags,
-         fd_t *fd, dict_t *xdata)
+int
+wb_readv (call_frame_t *frame, xlator_t *this, fd_t *fd, size_t size,
+          off_t offset, uint32_t flags, dict_t *xdata)
 {
-        wb_local_t *local    = NULL;
-        int32_t     op_errno = EINVAL;
+        wb_inode_t   *wb_inode     = NULL;
+        call_stub_t  *stub         = NULL;
 
-        local = mem_get0 (this->local_pool);
-        if (local == NULL) {
-                op_errno = ENOMEM;
-                goto unwind;
-        }
+        wb_inode = wb_inode_ctx_get (this, fd->inode);
+	if (!wb_inode)
+		goto noqueue;
 
-        local->flags = flags;
+	stub = fop_readv_stub (frame, wb_readv_helper, fd, size,
+			       offset, flags, xdata);
+	if (!stub)
+		goto unwind;
 
-        frame->local = local;
+	if (!wb_enqueue (wb_inode, stub))
+		goto unwind;
+
+	wb_process_queue (wb_inode);
 
-        STACK_WIND (frame, wb_open_cbk, FIRST_CHILD(this),
-                    FIRST_CHILD(this)->fops->open, loc, flags, fd, xdata);
         return 0;
 
 unwind:
-        STACK_UNWIND_STRICT (open, frame, -1, op_errno, NULL, NULL);
+        STACK_UNWIND_STRICT (readv, frame, -1, ENOMEM, NULL, 0, NULL, NULL,
+                             NULL);
         return 0;
-}
-
-
-int32_t
-wb_create_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
-               int32_t op_ret, int32_t op_errno, fd_t *fd, inode_t *inode,
-               struct iatt *buf, struct iatt *preparent,
-               struct iatt *postparent, dict_t *xdata)
-{
-        long        flags    = 0;
-        wb_inode_t *wb_inode = NULL;
-        wb_file_t  *file     = NULL;
-        wb_local_t *local    = NULL;
-
-        GF_ASSERT (frame);
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (frame->this->name, this, out,
-                                        op_errno, EINVAL);
-
-        if (op_ret != -1) {
-                if (frame->local) {
-                        flags = (long) frame->local;
-                }
-
-                file = wb_file_create (this, fd, flags);
-                if (file == NULL) {
-                        op_ret = -1;
-                        op_errno = ENOMEM;
-                        goto out;
-                }
-
-                LOCK (&inode->lock);
-                {
-                        wb_inode = __wb_inode_create (this, inode);
-                        if (wb_inode == NULL) {
-                                op_ret = -1;
-                                op_errno = ENOMEM;
-                        }
-                }
-                UNLOCK (&inode->lock);
-        }
-
-        frame->local = NULL;
-
-out:
-        STACK_UNWIND_STRICT (create, frame, op_ret, op_errno, fd, inode, buf,
-                             preparent, postparent, xdata);
-
-        if (local != NULL) {
-                mem_put (local);
-        }
 
+noqueue:
+        STACK_WIND (frame, default_readv_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->readv, fd, size, offset, flags,
+                    xdata);
         return 0;
 }
 
 
-int32_t
-wb_create (call_frame_t *frame, xlator_t *this, loc_t *loc, int32_t flags,
-           mode_t mode, mode_t umask, fd_t *fd, dict_t *xdata)
+int
+wb_flush_bg_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
+               int32_t op_ret, int32_t op_errno, dict_t *xdata)
 {
-        int32_t     op_errno = EINVAL;
-        wb_local_t *local    = NULL;
-
-        GF_ASSERT (frame);
-        GF_VALIDATE_OR_GOTO (frame->this->name, this, unwind);
-        GF_VALIDATE_OR_GOTO (frame->this->name, fd, unwind);
-        GF_VALIDATE_OR_GOTO (frame->this->name, loc, unwind);
-
-        local = mem_get0 (this->local_pool);
-        if (local == NULL) {
-                op_errno = ENOMEM;
-                goto unwind;
-        }
-
-        local->flags = flags;
-
-        frame->local = local;
-
-        STACK_WIND (frame, wb_create_cbk, FIRST_CHILD(this),
-                    FIRST_CHILD(this)->fops->create,
-                    loc, flags, mode, umask, fd, xdata);
-        return 0;
-
-unwind:
-        STACK_UNWIND_STRICT (create, frame, -1, op_errno, NULL, NULL, NULL,
-                             NULL, NULL, NULL);
+        STACK_DESTROY (frame->root);
         return 0;
 }
 
 
-/* Mark all the contiguous write requests for winding starting from head of
- * request list. Stops marking at the first non-write request found. If
- * file is opened with O_APPEND, make sure all the writes marked for winding
- * will fit into a single write call to server.
- */
-size_t
-__wb_mark_wind_all (wb_inode_t *wb_inode, list_head_t *list, list_head_t *winds)
+int
+wb_flush_helper (call_frame_t *frame, xlator_t *this, fd_t *fd, dict_t *xdata)
 {
-        wb_request_t     *request       = NULL, *prev_request = NULL;
-        wb_file_t        *wb_file       = NULL, *prev_wb_file = NULL;
-        wb_file_t        *last_wb_file  = NULL;
-        size_t            size          = 0;
-        char              first_request = 1, overlap = 0;
-        wb_conf_t        *conf          = NULL;
-        int               count         = 0;
-        enum _gf_boolean  dont_wind_set = 0;
-
-        GF_VALIDATE_OR_GOTO ("write-behind", wb_inode, out);
-        GF_VALIDATE_OR_GOTO (wb_inode->this->name, list, out);
-        GF_VALIDATE_OR_GOTO (wb_inode->this->name, winds, out);
-
-        conf = wb_inode->this->private;
-
-        list_for_each_entry (request, list, list)
-        {
-                if ((request->stub == NULL)
-                    || (request->stub->fop != GF_FOP_WRITE)) {
-                        break;
-                }
-
-                wb_file = wb_fd_ctx_get (wb_inode->this,
-                                         request->stub->args.writev.fd);
-                if (wb_file == NULL) {
-                        gf_log (wb_inode->this->name, GF_LOG_WARNING,
-                                "write behind wb_file pointer is"
-                                " not stored in context of fd(%p)",
-                                request->stub->args.writev.fd);
-                        goto out;
-                }
-
-                /* If write requests from two fds are interleaved, for
-                 * each of them, we can only send first set of adjacent
-                 * requests that are on same fd. This is because, fds
-                 * with O_APPEND cannot have more than one write fop in
-                 * progress while syncing, so that order is not messed
-                 * up. Since we group adjacent requests with same fd into
-                 * single write call whenever possible, we need the above said
-                 * measure.
-                 */
-                if ((prev_wb_file != NULL) && (prev_wb_file->flags & O_APPEND)
-                    && (prev_request->stub->args.writev.fd
-                        != request->stub->args.writev.fd)
-                    && (!prev_wb_file->dont_wind)) {
-                        prev_wb_file->dont_wind = 1;
-                        dont_wind_set = 1;
-                        last_wb_file = prev_wb_file;
-                }
-
-                prev_request = request;
-                prev_wb_file = wb_file;
-
-                if (!request->flags.write_request.stack_wound) {
-                        if (first_request) {
-                                first_request = 0;
-                        } else {
-                                overlap = wb_overlap (list, request);
-                                if (overlap) {
-                                        continue;
-                                }
-                        }
-
-                        if ((wb_file->flags & O_APPEND)
-                            && (((size + request->write_size)
-                                 > conf->aggregate_size)
-                                || ((count + request->stub->args.writev.count)
-                                    > MAX_VECTOR_COUNT)
-                                || (wb_file->dont_wind))) {
-                                continue;
-                        }
-
-                        size += request->write_size;
-
-                        wb_inode->aggregate_current -= request->write_size;
-
-                        count += request->stub->args.writev.count;
-
-                        request->flags.write_request.stack_wound = 1;
-                        list_add_tail (&request->winds, winds);
-                }
-        }
-
-out:
-        if (wb_inode != NULL) {
-                wb_inode->aggregate_current -= size;
-        }
-
-        if (dont_wind_set && (list != NULL)) {
-                list_for_each_entry (request, list, list) {
-                        wb_file = wb_fd_ctx_get (wb_inode->this,
-                                                 request->stub->args.writev.fd);
-                        if (wb_file != NULL) {
-                                wb_file->dont_wind = 0;
-                        }
-
-                        if (wb_file == last_wb_file) {
-                                break;
-                        }
-                }
-        }
-
-        return size;
-}
-
+        wb_conf_t    *conf        = NULL;
+        wb_inode_t   *wb_inode    = NULL;
+        call_frame_t *bg_frame    = NULL;
+	int           op_errno    = 0;
+	int           op_ret      = 0;
 
-int32_t
-__wb_can_wind (list_head_t *list, char *other_fop_in_queue,
-               char *overlapping_writes, char *incomplete_writes,
-               char *wind_all)
-{
-        wb_request_t *request         = NULL;
-        char          first_request   = 1;
-        int32_t       ret             = -1;
-        char          overlap         = 0;
+        conf = this->private;
 
-        GF_VALIDATE_OR_GOTO ("write-behind", list, out);
+	wb_inode = wb_inode_ctx_get (this, fd->inode);
+	if (!wb_inode) {
+		op_ret = -1;
+		op_errno = EINVAL;
+		goto unwind;
+	}
 
-        list_for_each_entry (request, list, list)
+        LOCK (&wb_inode->lock);
         {
-                if ((request->stub == NULL)
-                    || (request->stub->fop != GF_FOP_WRITE)) {
-                        if (request->stub && other_fop_in_queue) {
-                                *other_fop_in_queue = 1;
-                        }
-                        break;
-                }
-
-                if (request->flags.write_request.stack_wound
-                    && !request->flags.write_request.got_reply
-                    && (incomplete_writes != NULL)) {
-                        *incomplete_writes = 1;
-                        break;
-                }
+		if (wb_inode->op_ret < 0) {
+			op_ret = -1;
+			op_errno = wb_inode->op_errno;
+		}
 
-                if (!request->flags.write_request.stack_wound) {
-                        if (first_request) {
-                                char flush = 0;
-                                first_request = 0;
-
-                                flush = request->flags.write_request.flush_all;
-                                if (wind_all != NULL) {
-                                        *wind_all = flush;
-                                }
-                        }
-
-                        overlap = wb_overlap (list, request);
-                        if (overlap) {
-                                if (overlapping_writes != NULL) {
-                                        *overlapping_writes = 1;
-                                }
-
-                                break;
-                        }
-                }
+                wb_inode->op_ret = 0;
         }
+        UNLOCK (&wb_inode->lock);
 
-        ret = 0;
-out:
-        return ret;
-}
+	if (op_errno)
+		goto unwind;
 
+        if (conf->flush_behind)
+		goto flushbehind;
 
-ssize_t
-__wb_mark_winds (list_head_t *list, list_head_t *winds, size_t aggregate_conf,
-                 char enable_trickling_writes)
-{
-        size_t        size                   = 0;
-        char          other_fop_in_queue     = 0;
-        char          incomplete_writes      = 0;
-        char          overlapping_writes     = 0;
-        wb_request_t *request                = NULL;
-        wb_inode_t   *wb_inode               = NULL;
-        char          wind_all               = 0;
-        int32_t       ret                    = 0;
-
-        GF_VALIDATE_OR_GOTO ("write-behind", list, out);
-        GF_VALIDATE_OR_GOTO ("write-behind", winds, out);
-
-        if (list_empty (list)) {
-                goto out;
-        }
+	STACK_WIND (frame, default_flush_cbk, FIRST_CHILD(this),
+		    FIRST_CHILD(this)->fops->flush, fd, xdata);
+	return 0;
 
-        request = list_entry (list->next, typeof (*request), list);
-        wb_inode = request->wb_inode;
+flushbehind:
+	bg_frame = copy_frame (frame);
+	if (!bg_frame) {
+		op_ret = -1;
+		op_errno = ENOMEM;
+		goto unwind;
+	}
 
-        ret = __wb_can_wind (list, &other_fop_in_queue,
-                             &overlapping_writes, &incomplete_writes,
-                             &wind_all);
-        if (ret == -1) {
-                gf_log (wb_inode->this->name, GF_LOG_WARNING,
-                        "cannot decide whether to wind or not");
-                goto out;
-        }
-
-        if (!incomplete_writes && ((enable_trickling_writes)
-                                   || (wind_all) || (overlapping_writes)
-                                   || (other_fop_in_queue)
-                                   || (wb_inode->aggregate_current
-                                       >= aggregate_conf))) {
-                size = __wb_mark_wind_all (wb_inode, list, winds);
-        }
+	STACK_WIND (bg_frame, wb_flush_bg_cbk, FIRST_CHILD(this),
+		    FIRST_CHILD(this)->fops->flush, fd, xdata);
+	/* fall through */
+unwind:
+        STACK_UNWIND_STRICT (flush, frame, op_ret, op_errno, NULL);
 
-out:
-        return size;
+        return 0;
 }
 
 
-size_t
-__wb_mark_unwind_till (list_head_t *list, list_head_t *unwinds, size_t size)
+int
+wb_flush (call_frame_t *frame, xlator_t *this, fd_t *fd, dict_t *xdata)
 {
-        size_t        written_behind = 0;
-        wb_request_t *request        = NULL;
-        wb_inode_t   *wb_inode       = NULL;
-
-        if (list_empty (list)) {
-                goto out;
-        }
-
-        request = list_entry (list->next, typeof (*request), list);
-        wb_inode = request->wb_inode;
-
-        list_for_each_entry (request, list, list)
-        {
-                if ((request->stub == NULL)
-                    || (request->stub->fop != GF_FOP_WRITE)) {
-                        continue;
-                }
-
-                if (written_behind <= size) {
-                        if (!request->flags.write_request.write_behind) {
-                                written_behind += request->write_size;
-                                request->flags.write_request.write_behind = 1;
-                                list_add_tail (&request->unwinds, unwinds);
-
-                                if (!request->flags.write_request.got_reply) {
-                                        wb_inode->window_current
-                                                += request->write_size;
-                                }
-                        }
-                } else {
-                        break;
-                }
-        }
+        wb_inode_t   *wb_inode     = NULL;
+        call_stub_t  *stub         = NULL;
 
-out:
-        return written_behind;
-}
+        wb_inode = wb_inode_ctx_get (this, fd->inode);
+	if (!wb_inode)
+		goto noqueue;
 
+	stub = fop_flush_stub (frame, wb_flush_helper, fd, xdata);
+	if (!stub)
+		goto unwind;
 
-void
-__wb_mark_unwinds (list_head_t *list, list_head_t *unwinds)
-{
-        wb_request_t *request  = NULL;
-        wb_inode_t   *wb_inode = NULL;
+	if (!wb_enqueue (wb_inode, stub))
+		goto unwind;
 
-        GF_VALIDATE_OR_GOTO ("write-behind", list, out);
-        GF_VALIDATE_OR_GOTO ("write-behind", unwinds, out);
+	wb_process_queue (wb_inode);
 
-        if (list_empty (list)) {
-                goto out;
-        }
+        return 0;
 
-        request = list_entry (list->next, typeof (*request), list);
-        wb_inode = request->wb_inode;
+unwind:
+        STACK_UNWIND_STRICT (flush, frame, -1, ENOMEM, NULL);
 
-        if (wb_inode->window_current <= wb_inode->window_conf) {
-                __wb_mark_unwind_till (list, unwinds,
-                                       wb_inode->window_conf
-                                       - wb_inode->window_current);
-        }
+        return 0;
 
-out:
-        return;
+noqueue:
+        STACK_WIND (frame, default_flush_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->flush, fd, xdata);
+        return 0;
 }
 
 
-uint32_t
-__wb_get_other_requests (list_head_t *list, list_head_t *other_requests)
-{
-        wb_request_t *request = NULL;
-        uint32_t      count   = 0;
-
-        GF_VALIDATE_OR_GOTO ("write-behind", list, out);
-        GF_VALIDATE_OR_GOTO ("write-behind", other_requests, out);
-
-        list_for_each_entry (request, list, list) {
-                if ((request->stub == NULL)
-                    || (request->stub->fop == GF_FOP_WRITE)) {
-                        break;
-                }
-
-                if (!request->flags.other_requests.marked_for_resume) {
-                        request->flags.other_requests.marked_for_resume = 1;
-                        list_add_tail (&request->other_requests,
-                                       other_requests);
-                        count++;
-                }
-        }
 
-out:
-        return count;
-}
-
-
-int32_t
-wb_stack_unwind (list_head_t *unwinds)
+int
+wb_fsync_helper (call_frame_t *frame, xlator_t *this, fd_t *fd,
+                 int32_t datasync, dict_t *xdata)
 {
-        struct iatt   buf     = {0,};
-        wb_request_t *request = NULL, *dummy = NULL;
-        call_frame_t *frame   = NULL;
-        wb_local_t   *local   = NULL;
-        int           ret     = 0, write_requests_removed = 0;
-
-        GF_VALIDATE_OR_GOTO ("write-behind", unwinds, out);
-
-        list_for_each_entry_safe (request, dummy, unwinds, unwinds) {
-                frame = request->stub->frame;
-                local = frame->local;
-
-                STACK_UNWIND (frame, local->op_ret, local->op_errno,
-                              &buf, &buf, NULL, NULL);
-
-                ret = wb_request_unref (request);
-                if (ret == 0) {
-                        write_requests_removed++;
-                }
-        }
-
-out:
-        return write_requests_removed;
+        STACK_WIND (frame, default_fsync_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->fsync, fd, datasync, xdata);
+        return 0;
 }
 
 
-int32_t
-wb_resume_other_requests (call_frame_t *frame, wb_inode_t *wb_inode,
-                          list_head_t *other_requests)
+int
+wb_fsync (call_frame_t *frame, xlator_t *this, fd_t *fd, int32_t datasync,
+          dict_t *xdata)
 {
-        int32_t       ret          = -1;
-        wb_request_t *request      = NULL, *dummy = NULL;
-        int32_t       fops_removed = 0;
-        char          wind         = 0;
+        wb_inode_t   *wb_inode     = NULL;
         call_stub_t  *stub         = NULL;
 
-        GF_VALIDATE_OR_GOTO ((wb_inode ? wb_inode->this->name : "write-behind"),
-                             frame, out);
-        GF_VALIDATE_OR_GOTO (frame->this->name, wb_inode, out);
-        GF_VALIDATE_OR_GOTO (frame->this->name, other_requests, out);
-
-        if (list_empty (other_requests)) {
-                ret = 0;
-                goto out;
-        }
-
-        list_for_each_entry_safe (request, dummy, other_requests,
-                                  other_requests) {
-                wind = request->stub->wind;
-                stub = request->stub;
-
-                LOCK (&wb_inode->lock);
-                {
-                        request->stub = NULL;
-                }
-                UNLOCK (&wb_inode->lock);
-
-                if (!wind) {
-                        wb_request_unref (request);
-                        fops_removed++;
-                }
-
-                call_resume (stub);
-        }
-
-        ret = 0;
-
-        if (fops_removed > 0) {
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        gf_log (frame->this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-        }
-
-out:
-        return ret;
-}
-
-
-int32_t
-wb_do_ops (call_frame_t *frame, wb_inode_t *wb_inode, list_head_t *winds,
-           list_head_t *unwinds, list_head_t *other_requests)
-{
-        int32_t ret = -1, write_requests_removed = 0;
+        wb_inode = wb_inode_ctx_get (this, fd->inode);
+	if (!wb_inode)
+		goto noqueue;
 
-        GF_VALIDATE_OR_GOTO ((wb_inode ? wb_inode->this->name : "write-behind"),
-                             frame, out);
-        GF_VALIDATE_OR_GOTO (frame->this->name, wb_inode, out);
+	stub = fop_fsync_stub (frame, wb_fsync_helper, fd, datasync, xdata);
+	if (!stub)
+		goto unwind;
 
-        ret = wb_stack_unwind (unwinds);
+	if (!wb_enqueue (wb_inode, stub))
+		goto unwind;
 
-        write_requests_removed = ret;
+	wb_process_queue (wb_inode);
 
-        ret = wb_sync (frame, wb_inode, winds);
-        if (ret == -1) {
-                gf_log (frame->this->name, GF_LOG_WARNING,
-                        "syncing of write requests failed");
-        }
+        return 0;
 
-        ret = wb_resume_other_requests (frame, wb_inode, other_requests);
-        if (ret == -1) {
-                gf_log (frame->this->name, GF_LOG_WARNING,
-                        "cannot resume non-write requests in request queue");
-        }
+unwind:
+        STACK_UNWIND_STRICT (fsync, frame, -1, ENOMEM, NULL, NULL, NULL);
 
-        /* wb_stack_unwind does wb_request_unref after unwinding a write
-         * request. Hence if a write-request was just freed in wb_stack_unwind,
-         * we have to process request queue once again to unblock requests
-         * blocked on the writes just unwound.
-         */
-        if (write_requests_removed > 0) {
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        gf_log (frame->this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-        }
+        return 0;
 
-out:
-        return ret;
+noqueue:
+        STACK_WIND (frame, default_fsync_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->fsync, fd, datasync, xdata);
+        return 0;
 }
 
 
-inline int
-__wb_copy_into_holder (wb_request_t *holder, wb_request_t *request)
+int
+wb_stat_helper (call_frame_t *frame, xlator_t *this, loc_t *loc, dict_t *xdata)
 {
-        char          *ptr    = NULL;
-        struct iobuf  *iobuf  = NULL;
-        struct iobref *iobref = NULL;
-        int            ret    = -1;
-
-        if (holder->flags.write_request.virgin) {
-                /* TODO: check the required size */
-                iobuf = iobuf_get (request->wb_inode->this->ctx->iobuf_pool);
-                if (iobuf == NULL) {
-                        goto out;
-                }
-
-                iobref = iobref_new ();
-                if (iobref == NULL) {
-                        iobuf_unref (iobuf);
-                        goto out;
-                }
-
-                ret = iobref_add (iobref, iobuf);
-                if (ret != 0) {
-                        iobuf_unref (iobuf);
-                        iobref_unref (iobref);
-                        gf_log (request->wb_inode->this->name, GF_LOG_WARNING,
-                                "cannot add iobuf (%p) into iobref (%p)",
-                                iobuf, iobref);
-                        goto out;
-                }
-
-                iov_unload (iobuf->ptr, holder->stub->args.writev.vector,
-                            holder->stub->args.writev.count);
-                holder->stub->args.writev.vector[0].iov_base = iobuf->ptr;
-
-                iobref_unref (holder->stub->args.writev.iobref);
-                holder->stub->args.writev.iobref = iobref;
-
-                iobuf_unref (iobuf);
-
-                holder->flags.write_request.virgin = 0;
-        }
-
-        ptr = holder->stub->args.writev.vector[0].iov_base + holder->write_size;
-
-        iov_unload (ptr, request->stub->args.writev.vector,
-                    request->stub->args.writev.count);
-
-        holder->stub->args.writev.vector[0].iov_len += request->write_size;
-        holder->write_size += request->write_size;
-
-        request->flags.write_request.stack_wound = 1;
-        list_move_tail (&request->list, &request->wb_inode->passive_requests);
-
-        ret = 0;
-out:
-        return ret;
+        STACK_WIND (frame, default_stat_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->stat, loc, xdata);
+        return 0;
 }
 
 
-/* this procedure assumes that write requests have only one vector to write */
-void
-__wb_collapse_write_bufs (list_head_t *requests, size_t page_size)
+int
+wb_stat (call_frame_t *frame, xlator_t *this, loc_t *loc, dict_t *xdata)
 {
-        off_t         offset_expected = 0;
-        size_t        space_left      = 0;
-        wb_request_t *request         = NULL, *tmp = NULL, *holder = NULL;
-        int           ret             = 0;
-
-        GF_VALIDATE_OR_GOTO ("write-behind", requests, out);
-
-        list_for_each_entry_safe (request, tmp, requests, list) {
-                if ((request->stub == NULL)
-                    || (request->stub->fop != GF_FOP_WRITE)
-                    || (request->flags.write_request.stack_wound)) {
-                        holder = NULL;
-                        continue;
-                }
-
-                if (request->flags.write_request.write_behind) {
-                        if (holder == NULL) {
-                                holder = request;
-                                continue;
-                        }
-
-                        offset_expected = holder->stub->args.writev.off
-                                + holder->write_size;
-
-                        if ((request->stub->args.writev.off != offset_expected)
-                            || (!is_same_lkowner (&request->lk_owner,
-                                                  &holder->lk_owner))
-                            || (holder->stub->args.writev.fd
-                                != request->stub->args.writev.fd)) {
-                                holder = request;
-                                continue;
-                        }
-
-                        space_left = page_size - holder->write_size;
-
-                        if (space_left >= request->write_size) {
-                                ret = __wb_copy_into_holder (holder, request);
-                                if (ret != 0) {
-                                        break;
-                                }
-
-                                __wb_request_unref (request);
-                        } else {
-                                holder = request;
-                        }
-                } else {
-                        break;
-                }
-        }
-
-out:
-        return;
-}
+        wb_inode_t   *wb_inode     = NULL;
+        call_stub_t  *stub         = NULL;
 
 
-int32_t
-wb_process_queue (call_frame_t *frame, wb_inode_t *wb_inode)
-{
-        list_head_t winds  = {0, }, unwinds = {0, }, other_requests = {0, };
-        size_t      size   = 0;
-        wb_conf_t  *conf   = NULL;
-        uint32_t    count  = 0;
-        int32_t     ret    = -1;
+	wb_inode = wb_inode_ctx_get (this, loc->inode);
+        if (!wb_inode)
+		goto noqueue;
 
-        INIT_LIST_HEAD (&winds);
-        INIT_LIST_HEAD (&unwinds);
-        INIT_LIST_HEAD (&other_requests);
+	stub = fop_stat_stub (frame, wb_stat_helper, loc, xdata);
+	if (!stub)
+		goto unwind;
 
-        GF_VALIDATE_OR_GOTO ((wb_inode ? wb_inode->this->name : "write-behind"),
-                             frame, out);
-        GF_VALIDATE_OR_GOTO (wb_inode->this->name, frame, out);
+	if (!wb_enqueue (wb_inode, stub))
+		goto unwind;
 
-        conf = wb_inode->this->private;
-        GF_VALIDATE_OR_GOTO (wb_inode->this->name, conf, out);
+	wb_process_queue (wb_inode);
 
-        size = conf->aggregate_size;
-        LOCK (&wb_inode->lock);
-        {
-                /*
-                 * make sure requests are marked for unwinding and adjacent
-                 * contiguous write buffers (each of size less than that of
-                 * an iobuf) are packed properly so that iobufs are filled to
-                 * their maximum capacity, before calling __wb_mark_winds.
-                 */
-                __wb_mark_unwinds (&wb_inode->request, &unwinds);
-
-                __wb_collapse_write_bufs (&wb_inode->request,
-                                          wb_inode->this->ctx->page_size);
-
-                count = __wb_get_other_requests (&wb_inode->request,
-                                                 &other_requests);
-
-                if (count == 0) {
-                        __wb_mark_winds (&wb_inode->request, &winds, size,
-                                         conf->enable_trickling_writes);
-                }
+        return 0;
 
-        }
-        UNLOCK (&wb_inode->lock);
+unwind:
+        STACK_UNWIND_STRICT (stat, frame, -1, ENOMEM, NULL, NULL);
 
-        ret = wb_do_ops (frame, wb_inode, &winds, &unwinds, &other_requests);
+        if (stub)
+                call_stub_destroy (stub);
+        return 0;
 
-out:
-        return ret;
+noqueue:
+        STACK_WIND (frame, default_stat_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->stat, loc, xdata);
+	return 0;
 }
 
 
-int32_t
-wb_writev_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
-               int32_t op_ret, int32_t op_errno, struct iatt *prebuf,
-               struct iatt *postbuf, dict_t *xdata)
+int
+wb_fstat_helper (call_frame_t *frame, xlator_t *this, fd_t *fd, dict_t *xdata)
 {
-        GF_ASSERT (frame);
-
-        STACK_UNWIND_STRICT (writev, frame, op_ret, op_errno, prebuf, postbuf,
-                             xdata);
+        STACK_WIND (frame, default_fstat_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->fstat, fd, xdata);
         return 0;
 }
 
 
-int32_t
-wb_writev (call_frame_t *frame, xlator_t *this, fd_t *fd, struct iovec *vector,
-           int32_t count, off_t offset, uint32_t flags, struct iobref *iobref,
-           dict_t *xdata)
+int
+wb_fstat (call_frame_t *frame, xlator_t *this, fd_t *fd, dict_t *xdata)
 {
-        wb_inode_t   *wb_inode      = NULL;
-        wb_file_t    *wb_file       = NULL;
-        char          wb_disabled   = 0;
-        call_frame_t *process_frame = NULL;
-        call_stub_t  *stub          = NULL;
-        wb_local_t   *local         = NULL;
-        wb_request_t *request       = NULL;
-        int32_t       ret           = -1;
-        size_t        size          = 0;
-        int32_t       op_ret        = -1, op_errno = EINVAL;
-
-        GF_ASSERT (frame);
-
-        GF_VALIDATE_OR_GOTO_WITH_ERROR ("write-behind", this, unwind, op_errno,
-                                        EINVAL);
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (this->name, fd, unwind, op_errno,
-                                        EINVAL);
+        wb_inode_t   *wb_inode     = NULL;
+	call_stub_t  *stub         = NULL;
 
-        if (vector != NULL) {
-                size = iov_length (vector, count);
-        }
 
         wb_inode = wb_inode_ctx_get (this, fd->inode);
-        if ((!IA_ISDIR (fd->inode->ia_type)) && (wb_inode == NULL)) {
-                gf_log (this->name, GF_LOG_WARNING,
-                        "write behind wb_inode pointer is"
-                        " not stored in context of inode(%p), returning EBADFD",
-                        fd->inode);
-                op_errno = EBADFD;
-                goto unwind;
-        }
-
-        if (wb_file != NULL) {
-                if (wb_file->disabled || wb_file->disable_till) {
-                        if (size > wb_file->disable_till) {
-                                wb_file->disable_till = 0;
-                        } else {
-                                wb_file->disable_till -= size;
-                        }
-                        wb_disabled = 1;
-                }
-        } else {
-                wb_disabled = 1;
-        }
-
-        if (wb_inode != NULL) {
-                LOCK (&wb_inode->lock);
-                {
-                        op_ret = wb_inode->op_ret;
-                        op_errno = wb_inode->op_errno;
-                }
-                UNLOCK (&wb_inode->lock);
-        }
-
-        if (op_ret == -1) {
-                goto unwind;
-        }
-
-        if (wb_disabled) {
-                STACK_WIND (frame, wb_writev_cbk, FIRST_CHILD (frame->this),
-                            FIRST_CHILD (frame->this)->fops->writev,
-                            fd, vector, count, offset, flags, iobref, xdata);
-                return 0;
-        }
-
-        process_frame = copy_frame (frame);
-        if (process_frame == NULL) {
-                op_errno = ENOMEM;
-                goto unwind;
-        }
-
-        local = mem_get0 (this->local_pool);
-        if (local == NULL) {
-                op_errno = ENOMEM;
-                goto unwind;
-        }
+	if (!wb_inode)
+		goto noqueue;
 
-        frame->local = local;
-        local->wb_inode = wb_inode;
+	stub = fop_fstat_stub (frame, wb_fstat_helper, fd, xdata);
+	if (!stub)
+		goto unwind;
 
-        stub = fop_writev_stub (frame, NULL, fd, vector, count, offset, flags,
-                                iobref, xdata);
-        if (stub == NULL) {
-                op_errno = ENOMEM;
-                goto unwind;
-        }
+	if (!wb_enqueue (wb_inode, stub))
+		goto unwind;
 
-        request = wb_enqueue (wb_inode, stub);
-        if (request == NULL) {
-                op_errno = ENOMEM;
-                goto unwind;
-        }
-
-        ret = wb_process_queue (process_frame, wb_inode);
-        if (ret == -1) {
-                gf_log (this->name, GF_LOG_WARNING,
-                        "request queue processing failed");
-        }
-
-        STACK_DESTROY (process_frame->root);
+	wb_process_queue (wb_inode);
 
         return 0;
 
 unwind:
-        local = frame->local;
-        frame->local = NULL;
-        mem_put (local);
-
-        STACK_UNWIND_STRICT (writev, frame, -1, op_errno, NULL, NULL, NULL);
+        STACK_UNWIND_STRICT (fstat, frame, -1, ENOMEM, NULL, NULL);
 
-        if (process_frame) {
-                STACK_DESTROY (process_frame->root);
-        }
-
-        if (stub) {
+        if (stub)
                 call_stub_destroy (stub);
-        }
-
         return 0;
-}
-
-
-int32_t
-wb_readv_cbk (call_frame_t *frame, void *cookie, xlator_t *this, int32_t op_ret,
-              int32_t op_errno, struct iovec *vector, int32_t count,
-              struct iatt *stbuf, struct iobref *iobref, dict_t *xdata)
-{
-        wb_local_t   *local    = NULL;
-        wb_inode_t   *wb_inode = NULL;
-        wb_request_t *request  = NULL;
-        int32_t       ret      = 0;
-
-        GF_ASSERT (frame);
-
-        local = frame->local;
-        wb_inode = local->wb_inode;
-        request = local->request;
-
-        if ((request != NULL) && (wb_inode != NULL)) {
-                wb_request_unref (request);
-
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        if (errno == ENOMEM) {
-                                op_ret = -1;
-                                op_errno = ENOMEM;
-                        }
-
-                        gf_log (frame->this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-        }
-
-        STACK_UNWIND_STRICT (readv, frame, op_ret, op_errno, vector, count,
-                             stbuf, iobref, xdata);
 
+noqueue:
+        STACK_WIND (frame, default_fstat_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->fstat, fd, xdata);
         return 0;
 }
 
 
-static int32_t
-wb_readv_helper (call_frame_t *frame, xlator_t *this, fd_t *fd, size_t size,
-                 off_t offset, uint32_t flags, dict_t *xdata)
+int
+wb_truncate_helper (call_frame_t *frame, xlator_t *this, loc_t *loc,
+                    off_t offset, dict_t *xdata)
 {
-        STACK_WIND (frame, wb_readv_cbk, FIRST_CHILD(this),
-                    FIRST_CHILD(this)->fops->readv, fd, size, offset, flags,
-                    xdata);
-
+        STACK_WIND (frame, default_truncate_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->truncate, loc, offset, xdata);
         return 0;
 }
 
 
-int32_t
-wb_readv (call_frame_t *frame, xlator_t *this, fd_t *fd, size_t size,
-          off_t offset, uint32_t flags, dict_t *xdata)
+int
+wb_truncate (call_frame_t *frame, xlator_t *this, loc_t *loc, off_t offset,
+             dict_t *xdata)
 {
         wb_inode_t   *wb_inode     = NULL;
-        wb_local_t   *local        = NULL;
-        call_stub_t  *stub         = NULL;
-        int32_t       ret          = -1, op_errno = 0;
-        wb_request_t *request      = NULL;
-
-        GF_ASSERT (frame);
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (frame->this->name, this, unwind,
-                                        op_errno, EINVAL);
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (this->name, fd, unwind, op_errno,
-                                        EINVAL);
-
-        wb_inode = wb_inode_ctx_get (this, fd->inode);
-        if ((!IA_ISDIR (fd->inode->ia_type)) && (wb_inode == NULL)) {
-                gf_log (this->name, GF_LOG_WARNING,
-                        "write behind wb_inode pointer is"
-                        " not stored in context of inode(%p), returning "
-                        "EBADFD", fd->inode);
-                op_errno = EBADFD;
-                goto unwind;
-        }
-
-        local = mem_get0 (this->local_pool);
-        if (local == NULL) {
-                op_errno = ENOMEM;
-                goto unwind;
-        }
+	call_stub_t  *stub         = NULL;
 
-        local->wb_inode = wb_inode;
+	wb_inode = wb_inode_create (this, loc->inode);
+	if (!wb_inode)
+		goto unwind;
 
-        frame->local = local;
-        if (wb_inode) {
-                stub = fop_readv_stub (frame, wb_readv_helper, fd, size,
-                                       offset, flags, xdata);
-                if (stub == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
+	stub = fop_truncate_stub (frame, wb_truncate_helper, loc,
+				  offset, xdata);
+	if (!stub)
+		goto unwind;
 
-                request = wb_enqueue (wb_inode, stub);
-                if (request == NULL) {
-                        call_stub_destroy (stub);
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
+	if (!wb_enqueue (wb_inode, stub))
+		goto unwind;
 
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-        } else {
-                STACK_WIND (frame, wb_readv_cbk, FIRST_CHILD(this),
-                            FIRST_CHILD(this)->fops->readv,
-                            fd, size, offset, flags, xdata);
-        }
+	wb_process_queue (wb_inode);
 
         return 0;
 
 unwind:
-        STACK_UNWIND_STRICT (readv, frame, -1, op_errno, NULL, 0, NULL, NULL,
-                             NULL);
-        return 0;
-}
-
-
-int32_t
-wb_ffr_bg_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
-               int32_t op_ret, int32_t op_errno, dict_t *xdata)
-{
-        STACK_DESTROY (frame->root);
-        return 0;
-}
-
+        STACK_UNWIND_STRICT (truncate, frame, -1, ENOMEM, NULL, NULL, NULL);
 
-int32_t
-wb_ffr_cbk (call_frame_t *frame, void *cookie, xlator_t *this, int32_t op_ret,
-            int32_t op_errno, dict_t *xdata)
-{
-        wb_local_t *local    = NULL;
-        wb_inode_t *wb_inode = NULL;
-
-        GF_ASSERT (frame);
-
-        local = frame->local;
-        wb_inode = local->wb_inode;
-
-        if (wb_inode != NULL) {
-                LOCK (&wb_inode->lock);
-                {
-                        if (wb_inode->op_ret == -1) {
-                                op_ret = wb_inode->op_ret;
-                                op_errno = wb_inode->op_errno;
-
-                                wb_inode->op_ret = 0;
-                        }
-                }
-                UNLOCK (&wb_inode->lock);
-        }
-
-        STACK_UNWIND_STRICT (flush, frame, op_ret, op_errno, xdata);
+        if (stub)
+                call_stub_destroy (stub);
 
         return 0;
 }
 
 
-int32_t
-wb_flush_helper (call_frame_t *frame, xlator_t *this, fd_t *fd, dict_t *xdata)
+int
+wb_ftruncate_helper (call_frame_t *frame, xlator_t *this, fd_t *fd,
+                     off_t offset, dict_t *xdata)
 {
-        wb_conf_t    *conf        = NULL;
-        wb_local_t   *local       = NULL;
-        wb_inode_t   *wb_inode    = NULL;
-        call_frame_t *flush_frame = NULL, *process_frame = NULL;
-        int32_t       op_ret      = -1, op_errno = -1, ret = -1;
-
-        GF_ASSERT (frame);
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (frame->this->name, this, unwind,
-                                        op_errno, EINVAL);
-
-        conf = this->private;
-
-        local = frame->local;
-        wb_inode = local->wb_inode;
-
-        LOCK (&wb_inode->lock);
-        {
-                op_ret = wb_inode->op_ret;
-                op_errno = wb_inode->op_errno;
-        }
-        UNLOCK (&wb_inode->lock);
-
-        if (local && local->request) {
-                process_frame = copy_frame (frame);
-                if (process_frame == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
-
-                wb_request_unref (local->request);
-        }
-
-        if (conf->flush_behind) {
-                flush_frame = copy_frame (frame);
-                if (flush_frame == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
-
-                STACK_WIND (flush_frame, wb_ffr_bg_cbk, FIRST_CHILD(this),
-                            FIRST_CHILD(this)->fops->flush, fd, xdata);
-        } else {
-                STACK_WIND (frame, wb_ffr_cbk, FIRST_CHILD(this),
-                            FIRST_CHILD(this)->fops->flush, fd, xdata);
-        }
-
-        if (process_frame != NULL) {
-                ret = wb_process_queue (process_frame, wb_inode);
-                if (ret == -1) {
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-
-                STACK_DESTROY (process_frame->root);
-        }
-
-        if (conf->flush_behind) {
-                STACK_UNWIND_STRICT (flush, frame, op_ret, op_errno, NULL);
-        }
-
-        return 0;
-
-unwind:
-        STACK_UNWIND_STRICT (flush, frame, -1, op_errno, NULL);
+        STACK_WIND (frame, default_ftruncate_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->ftruncate, fd, offset, xdata);
         return 0;
 }
 
 
-int32_t
-wb_flush (call_frame_t *frame, xlator_t *this, fd_t *fd, dict_t *xdata)
+int
+wb_ftruncate (call_frame_t *frame, xlator_t *this, fd_t *fd, off_t offset,
+              dict_t *xdata)
 {
-        wb_conf_t    *conf         = NULL;
         wb_inode_t   *wb_inode     = NULL;
-        wb_local_t   *local        = NULL;
         call_stub_t  *stub         = NULL;
-        call_frame_t *flush_frame  = NULL;
-        wb_request_t *request      = NULL;
-        int32_t       ret          = 0, op_errno = 0;
-
-        GF_ASSERT (frame);
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (frame->this->name, this, unwind,
-                                        op_errno, EINVAL);
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (this->name, fd, unwind, op_errno,
-                                        EINVAL);
-
-        conf = this->private;
-
-        wb_inode = wb_inode_ctx_get (this, fd->inode);
-        if ((!IA_ISDIR (fd->inode->ia_type)) && (wb_inode == NULL)) {
-                gf_log (this->name, GF_LOG_WARNING,
-                        "write behind wb_inode pointer is"
-                        " not stored in context of inode(%p), "
-                        "returning EBADFD", fd->inode);
-                op_errno = EBADFD;
-                goto unwind;
-        }
-
-        if (wb_inode != NULL) {
-                local = mem_get0 (this->local_pool);
-                if (local == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
-
-                local->wb_inode = wb_inode;
 
-                frame->local = local;
+        wb_inode = wb_inode_create (this, fd->inode);
+	if (!wb_inode)
+		goto unwind;
 
-                stub = fop_flush_stub (frame, wb_flush_helper, fd, xdata);
-                if (stub == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
+	stub = fop_ftruncate_stub (frame, wb_ftruncate_helper, fd,
+				   offset, xdata);
+	if (!stub)
+		goto unwind;
 
-                request = wb_enqueue (wb_inode, stub);
-                if (request == NULL) {
-                        call_stub_destroy (stub);
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
+	if (!wb_enqueue (wb_inode, stub))
+		goto unwind;
 
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-        } else {
-                if (conf->flush_behind) {
-                        flush_frame = copy_frame (frame);
-                        if (flush_frame == NULL) {
-                                op_errno = ENOMEM;
-                                goto unwind;
-                        }
-
-                        STACK_UNWIND_STRICT (flush, frame, 0, 0, NULL);
-
-                        STACK_WIND (flush_frame, wb_ffr_bg_cbk,
-                                    FIRST_CHILD(this),
-                                    FIRST_CHILD(this)->fops->flush, fd, xdata);
-                } else {
-                        STACK_WIND (frame, wb_ffr_cbk, FIRST_CHILD(this),
-                                    FIRST_CHILD(this)->fops->flush, fd, xdata);
-                }
-        }
+	wb_process_queue (wb_inode);
 
         return 0;
 
 unwind:
-        STACK_UNWIND_STRICT (flush, frame, -1, op_errno, NULL);
-        return 0;
-}
-
-
-static int32_t
-wb_fsync_cbk (call_frame_t *frame, void *cookie, xlator_t *this, int32_t op_ret,
-              int32_t op_errno, struct iatt *prebuf, struct iatt *postbuf,
-              dict_t *xdata)
-{
-        wb_local_t   *local    = NULL;
-        wb_inode_t   *wb_inode = NULL;
-        wb_request_t *request  = NULL;
-        int32_t       ret      = -1;
-
-        GF_ASSERT (frame);
-
-        local = frame->local;
-        wb_inode = local->wb_inode;
-        request = local->request;
-
-        if (wb_inode != NULL) {
-                LOCK (&wb_inode->lock);
-                {
-                        if (wb_inode->op_ret == -1) {
-                                op_ret = wb_inode->op_ret;
-                                op_errno = wb_inode->op_errno;
-
-                                wb_inode->op_ret = 0;
-                        }
-                }
-                UNLOCK (&wb_inode->lock);
-
-                if (request) {
-                        wb_request_unref (request);
-                        ret = wb_process_queue (frame, wb_inode);
-                        if (ret == -1) {
-                                if (errno == ENOMEM) {
-                                        op_ret = -1;
-                                        op_errno = ENOMEM;
-                                }
-
-                                gf_log (this->name, GF_LOG_WARNING,
-                                        "request queue processing failed");
-                        }
-                }
-
-        }
-
-        STACK_UNWIND_STRICT (fsync, frame, op_ret, op_errno, prebuf, postbuf,
-                             xdata);
+        STACK_UNWIND_STRICT (ftruncate, frame, -1, ENOMEM, NULL, NULL, NULL);
 
+        if (stub)
+                call_stub_destroy (stub);
         return 0;
 }
 
 
-static int32_t
-wb_fsync_helper (call_frame_t *frame, xlator_t *this, fd_t *fd,
-                 int32_t datasync, dict_t *xdata)
+int
+wb_setattr_helper (call_frame_t *frame, xlator_t *this, loc_t *loc,
+                   struct iatt *stbuf, int32_t valid, dict_t *xdata)
 {
-        STACK_WIND (frame, wb_fsync_cbk, FIRST_CHILD(this),
-                    FIRST_CHILD(this)->fops->fsync, fd, datasync, xdata);
+        STACK_WIND (frame, default_setattr_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->setattr, loc, stbuf, valid, xdata);
         return 0;
 }
 
 
-int32_t
-wb_fsync (call_frame_t *frame, xlator_t *this, fd_t *fd, int32_t datasync,
-          dict_t *xdata)
+int
+wb_setattr (call_frame_t *frame, xlator_t *this, loc_t *loc,
+            struct iatt *stbuf, int32_t valid, dict_t *xdata)
 {
         wb_inode_t   *wb_inode     = NULL;
-        wb_local_t   *local        = NULL;
         call_stub_t  *stub         = NULL;
-        wb_request_t *request      = NULL;
-        int32_t       ret          = -1, op_errno = 0;
-
-        GF_ASSERT (frame);
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (frame->this->name, this, unwind,
-                                        op_errno, EINVAL);
-        GF_VALIDATE_OR_GOTO_WITH_ERROR (frame->this->name, fd, unwind,
-                                        op_errno, EINVAL);
 
-        wb_inode = wb_inode_ctx_get (this, fd->inode);
-        if (wb_inode == NULL && (!IA_ISDIR (fd->inode->ia_type))) {
-                gf_log (this->name, GF_LOG_WARNING,
-                        "write behind wb_inode pointer is"
-                        " not stored in context of inode(%p), "
-                        "returning EBADFD", fd->inode);
-                op_errno = EBADFD;
-                goto unwind;
-        }
+	wb_inode = wb_inode_ctx_get (this, loc->inode);
+	if (!wb_inode)
+		goto noqueue;
 
-        local = mem_get0 (this->local_pool);
-        if (local == NULL) {
-                op_errno = ENOMEM;
-                goto unwind;
-        }
-
-        frame->local = local;
-        local->wb_inode = wb_inode;
-
-        if (wb_inode) {
-                stub = fop_fsync_stub (frame, wb_fsync_helper, fd, datasync,
-                                       xdata);
-                if (stub == NULL) {
-                        op_errno = ENOMEM;
-                        goto unwind;
-                }
+	stub = fop_setattr_stub (frame, wb_setattr_helper, loc, stbuf,
+                                         valid, xdata);
+	if (!stub)
+		goto unwind;
 
-                request = wb_enqueue (wb_inode, stub);
-                if (request == NULL) {
-                        op_errno = ENOMEM;
-                        call_stub_destroy (stub);
-                        goto unwind;
-                }
+	if (!wb_enqueue (wb_inode, stub))
+		goto unwind;
 
-                ret = wb_process_queue (frame, wb_inode);
-                if (ret == -1) {
-                        gf_log (this->name, GF_LOG_WARNING,
-                                "request queue processing failed");
-                }
-        } else {
-                STACK_WIND (frame, wb_fsync_cbk, FIRST_CHILD(this),
-                            FIRST_CHILD(this)->fops->fsync, fd, datasync,
-                            xdata);
-        }
+	wb_process_queue (wb_inode);
 
         return 0;
-
 unwind:
-        STACK_UNWIND_STRICT (fsync, frame, -1, op_errno, NULL, NULL, NULL);
-        return 0;
-}
-
-
-int32_t
-wb_readdirp_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
-                 int32_t op_ret, int32_t op_errno, gf_dirent_t *entries,
-                 dict_t *xdata)
-{
-        gf_dirent_t *entry      = NULL;
-
-        if (op_ret <= 0) {
-                goto unwind;
-        }
+        STACK_UNWIND_STRICT (setattr, frame, -1, ENOMEM, NULL, NULL, NULL);
 
-        list_for_each_entry (entry, &entries->list, list) {
-                if (!entry->inode)
-			continue;
-                wb_inode_create (this, entry->inode);
-        }
+        if (stub)
+                call_stub_destroy (stub);
+	return 0;
 
-unwind:
-        STACK_UNWIND_STRICT (readdirp, frame, op_ret, op_errno, entries, xdata);
+noqueue:
+        STACK_WIND (frame, default_setattr_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->setattr, loc, stbuf, valid, xdata);
         return 0;
 }
 
 
-int32_t
-wb_readdirp (call_frame_t *frame, xlator_t *this, fd_t *fd,
-             size_t size, off_t off, dict_t *xdata)
+int
+wb_fsetattr_helper (call_frame_t *frame, xlator_t *this, fd_t *fd,
+		    struct iatt *stbuf, int32_t valid, dict_t *xdata)
 {
-        STACK_WIND (frame, wb_readdirp_cbk, FIRST_CHILD(this),
-                    FIRST_CHILD(this)->fops->readdirp, fd, size, off, xdata);
+        STACK_WIND (frame, default_fsetattr_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->fsetattr, fd, stbuf, valid, xdata);
         return 0;
 }
 
 
-int32_t
-wb_release (xlator_t *this, fd_t *fd)
+int
+wb_fsetattr (call_frame_t *frame, xlator_t *this, fd_t *fd,
+	     struct iatt *stbuf, int32_t valid, dict_t *xdata)
 {
-        uint64_t    wb_file_ptr = 0;
-        wb_file_t  *wb_file      = NULL;
+        wb_inode_t   *wb_inode     = NULL;
+        call_stub_t  *stub         = NULL;
 
-        GF_VALIDATE_OR_GOTO ("write-behind", this, out);
-        GF_VALIDATE_OR_GOTO (this->name, fd, out);
+	wb_inode = wb_inode_ctx_get (this, fd->inode);
+	if (!wb_inode)
+		goto noqueue;
 
-        fd_ctx_del (fd, this, &wb_file_ptr);
-        wb_file = (wb_file_t *)(long) wb_file_ptr;
+	stub = fop_fsetattr_stub (frame, wb_fsetattr_helper, fd, stbuf,
+				  valid, xdata);
+	if (!stub)
+		goto unwind;
 
-        GF_FREE (wb_file);
+	if (!wb_enqueue (wb_inode, stub))
+		goto unwind;
 
-out:
+	wb_process_queue (wb_inode);
+
+        return 0;
+unwind:
+        STACK_UNWIND_STRICT (fsetattr, frame, -1, ENOMEM, NULL, NULL, NULL);
+
+        if (stub)
+                call_stub_destroy (stub);
+	return 0;
+
+noqueue:
+        STACK_WIND (frame, default_fsetattr_cbk, FIRST_CHILD(this),
+                    FIRST_CHILD(this)->fops->fsetattr, fd, stbuf, valid, xdata);
         return 0;
 }
 
 
-int32_t
+int
 wb_forget (xlator_t *this, inode_t *inode)
 {
         uint64_t    tmp      = 0;
@@ -2917,15 +1639,16 @@ wb_forget (xlator_t *this, inode_t *inode)
 
         wb_inode = (wb_inode_t *)(long)tmp;
 
-        if (wb_inode != NULL) {
-                LOCK (&wb_inode->lock);
-                {
-                        GF_ASSERT (list_empty (&wb_inode->request));
-                }
-                UNLOCK (&wb_inode->lock);
+	if (!wb_inode)
+		return 0;
 
-                wb_inode_destroy (wb_inode);
-        }
+	LOCK (&wb_inode->lock);
+	{
+		GF_ASSERT (list_empty (&wb_inode->todo));
+		GF_ASSERT (list_empty (&wb_inode->liability));
+		GF_ASSERT (list_empty (&wb_inode->temptation));
+	}
+	UNLOCK (&wb_inode->lock);
 
         return 0;
 }
@@ -2950,10 +1673,8 @@ wb_priv_dump (xlator_t *this)
 
         gf_proc_dump_write ("aggregate_size", "%d", conf->aggregate_size);
         gf_proc_dump_write ("window_size", "%d", conf->window_size);
-        gf_proc_dump_write ("enable_O_SYNC", "%d", conf->enable_O_SYNC);
         gf_proc_dump_write ("flush_behind", "%d", conf->flush_behind);
-        gf_proc_dump_write ("enable_trickling_writes", "%d",
-                            conf->enable_trickling_writes);
+        gf_proc_dump_write ("trickling_writes", "%d", conf->trickling_writes);
 
         ret = 0;
 out:
@@ -2962,48 +1683,45 @@ out:
 
 
 void
-__wb_dump_requests (struct list_head *head, char *prefix, char passive)
+__wb_dump_requests (struct list_head *head, char *prefix)
 {
         char          key[GF_DUMP_MAX_BUF_LEN]        = {0, };
         char          key_prefix[GF_DUMP_MAX_BUF_LEN] = {0, }, flag = 0;
-        wb_request_t *request                         = NULL;
+        wb_request_t *req                             = NULL;
 
-        list_for_each_entry (request, head, list) {
-                gf_proc_dump_build_key (key, prefix, passive ? "passive-request"
-                                        : "active-request");
+        list_for_each_entry (req, head, all) {
                 gf_proc_dump_build_key (key_prefix, key,
-                                        (char *)gf_fop_list[request->fop]);
+                                        (char *)gf_fop_list[req->fop]);
 
                 gf_proc_dump_add_section(key_prefix);
 
-                gf_proc_dump_write ("request-ptr", "%p", request);
+                gf_proc_dump_write ("request-ptr", "%p", req);
 
-                gf_proc_dump_write ("refcount", "%d", request->refcount);
+                gf_proc_dump_write ("refcount", "%d", req->refcount);
 
-                if (request->fop == GF_FOP_WRITE) {
-                        flag = request->flags.write_request.stack_wound;
-                        gf_proc_dump_write ("stack_wound", "%d", flag);
+		if (list_empty (&req->todo))
+			gf_proc_dump_write ("wound", "yes");
+		else
+			gf_proc_dump_write ("wound", "no");
 
+                if (req->fop == GF_FOP_WRITE) {
                         gf_proc_dump_write ("size", "%"GF_PRI_SIZET,
-                                            request->write_size);
+                                            req->write_size);
 
                         gf_proc_dump_write ("offset", "%"PRId64,
-                                            request->stub->args.writev.off);
+                                            req->stub->args.writev.off);
 
-                        flag = request->flags.write_request.write_behind;
-                        gf_proc_dump_write ("write_behind", "%d", flag);
+                        flag = req->ordering.lied;
+                        gf_proc_dump_write ("lied", "%d", flag);
 
-                        flag = request->flags.write_request.got_reply;
-                        gf_proc_dump_write ("got_reply", "%d", flag);
+                        flag = req->ordering.append;
+                        gf_proc_dump_write ("append", "%d", flag);
 
-                        flag = request->flags.write_request.virgin;
-                        gf_proc_dump_write ("virgin", "%d", flag);
+                        flag = req->ordering.fulfilled;
+                        gf_proc_dump_write ("fulfilled", "%d", flag);
 
-                        flag = request->flags.write_request.flush_all;
-                        gf_proc_dump_write ("flush_all", "%d", flag);
-                } else {
-                        flag = request->flags.other_requests.marked_for_resume;
-                        gf_proc_dump_write ("marked_for_resume", "%d", flag);
+                        flag = req->ordering.go;
+                        gf_proc_dump_write ("go", "%d", flag);
                 }
         }
 }
@@ -3047,22 +1765,14 @@ wb_inode_dump (xlator_t *this, inode_t *inode)
         gf_proc_dump_write ("window_current", "%"GF_PRI_SIZET,
                             wb_inode->window_current);
 
-        gf_proc_dump_write ("aggregate_current", "%"GF_PRI_SIZET,
-                            wb_inode->aggregate_current);
-
         gf_proc_dump_write ("op_ret", "%d", wb_inode->op_ret);
 
         gf_proc_dump_write ("op_errno", "%d", wb_inode->op_errno);
 
         LOCK (&wb_inode->lock);
         {
-                if (!list_empty (&wb_inode->request)) {
-                        __wb_dump_requests (&wb_inode->request, key_prefix, 0);
-                }
-
-                if (!list_empty (&wb_inode->passive_requests)) {
-                        __wb_dump_requests (&wb_inode->passive_requests,
-                                            key_prefix, 1);
+                if (!list_empty (&wb_inode->all)) {
+                        __wb_dump_requests (&wb_inode->all, key_prefix);
                 }
         }
         UNLOCK (&wb_inode->lock);
@@ -3074,65 +1784,6 @@ out:
 
 
 int
-wb_fd_dump (xlator_t *this, fd_t *fd)
-{
-        wb_file_t  *wb_file                        = NULL;
-        char       *path                           = NULL;
-        char       key_prefix[GF_DUMP_MAX_BUF_LEN] = {0, };
-        int        ret                             = -1;
-        gf_boolean_t  section_added                = _gf_false;
-
-        gf_proc_dump_build_key (key_prefix, "xlator.performance.write-behind",
-                                "wb_file");
-
-        if ((fd == NULL) || (this == NULL)) {
-                goto out;
-        }
-
-        ret = TRY_LOCK(&fd->lock);
-        if (ret)
-                goto out;
-        {
-                wb_file = __wb_fd_ctx_get (this, fd);
-        }
-        UNLOCK(&fd->lock);
-
-        if (wb_file == NULL) {
-                goto out;
-        }
-
-        gf_proc_dump_add_section (key_prefix);
-        section_added = _gf_true;
-
-        __inode_path (fd->inode, NULL, &path);
-        if (path != NULL) {
-                gf_proc_dump_write ("path", "%s", path);
-                GF_FREE (path);
-        }
-
-        gf_proc_dump_write ("fd", "%p", fd);
-
-        gf_proc_dump_write ("flags", "%d", wb_file->flags);
-
-        gf_proc_dump_write ("flags", "%s",
-                            (wb_file->flags & O_APPEND) ? "O_APPEND"
-                            : "!O_APPEND");
-
-        gf_proc_dump_write ("disabled", "%d", wb_file->disabled);
-
-out:
-        if (ret && fd && this) {
-                if (_gf_false == section_added)
-                        gf_proc_dump_add_section (key_prefix);
-                gf_proc_dump_write ("Unable to dump the fd",
-                                    "(Lock acquisition failed) %s",
-                                    uuid_utoa (fd->inode->gfid));
-        }
-        return 0;
-}
-
-
-int32_t
 mem_acct_init (xlator_t *this)
 {
         int     ret = -1;
@@ -3166,6 +1817,14 @@ reconfigure (xlator_t *this, dict_t *options)
         GF_OPTION_RECONF ("flush-behind", conf->flush_behind, options, bool,
                           out);
 
+        GF_OPTION_RECONF ("trickling-writes", conf->trickling_writes, options,
+			  bool, out);
+
+        GF_OPTION_RECONF ("strict-O_DIRECT", conf->strict_O_DIRECT, options,
+			  bool, out);
+
+        GF_OPTION_RECONF ("strict-write-ordering", conf->strict_write_ordering,
+			  options, bool, out);
         ret = 0;
 out:
         return ret;
@@ -3196,8 +1855,6 @@ init (xlator_t *this)
                 goto out;
         }
 
-        GF_OPTION_INIT("enable-O_SYNC", conf->enable_O_SYNC, bool, out);
-
         /* configure 'options aggregate-size <size>' */
         conf->aggregate_size = WB_AGGREGATE_SIZE;
 
@@ -3223,16 +1880,12 @@ init (xlator_t *this)
         /* configure 'option flush-behind <on/off>' */
         GF_OPTION_INIT ("flush-behind", conf->flush_behind, bool, out);
 
-        GF_OPTION_INIT ("enable-trickling-writes",
-                        conf->enable_trickling_writes, bool, out);
+        GF_OPTION_INIT ("trickling-writes", conf->trickling_writes, bool, out);
 
-        this->local_pool = mem_pool_new (wb_local_t, 64);
-        if (!this->local_pool) {
-                ret = -1;
-                gf_log (this->name, GF_LOG_ERROR,
-                        "failed to create local_t's memory pool");
-                goto out;
-        }
+        GF_OPTION_INIT ("strict-O_DIRECT", conf->strict_O_DIRECT, bool, out);
+
+        GF_OPTION_INIT ("strict-write-ordering", conf->strict_write_ordering,
+			bool, out);
 
         this->private = conf;
         ret = 0;
@@ -3266,10 +1919,7 @@ out:
 
 
 struct xlator_fops fops = {
-        .lookup      = wb_lookup,
         .writev      = wb_writev,
-        .open        = wb_open,
-        .create      = wb_create,
         .readv       = wb_readv,
         .flush       = wb_flush,
         .fsync       = wb_fsync,
@@ -3278,20 +1928,21 @@ struct xlator_fops fops = {
         .truncate    = wb_truncate,
         .ftruncate   = wb_ftruncate,
         .setattr     = wb_setattr,
-        .readdirp    = wb_readdirp,
+        .fsetattr    = wb_fsetattr,
 };
 
+
 struct xlator_cbks cbks = {
         .forget   = wb_forget,
-        .release  = wb_release,
 };
 
+
 struct xlator_dumpops dumpops = {
         .priv      =  wb_priv_dump,
         .inodectx  =  wb_inode_dump,
-        .fdctx     =  wb_fd_dump,
 };
 
+
 struct volume_options options[] = {
         { .key  = {"flush-behind"},
           .type = GF_OPTION_TYPE_BOOL,
@@ -3300,7 +1951,7 @@ struct volume_options options[] = {
                           "translator to perform flush in background, by "
                           "returning success (or any errors, if any of "
                           "previous  writes were failed) to application even "
-                          "before flush is sent to backend filesystem. "
+                          "before flush FOP is sent to backend filesystem. "
         },
         { .key  = {"cache-size", "window-size"},
           .type = GF_OPTION_TYPE_SIZET,
@@ -3309,21 +1960,20 @@ struct volume_options options[] = {
           .default_value = "1MB",
           .description = "Size of the write-behind buffer for a single file "
                          "(inode)."
-
-        },
-        { .key = {"disable-for-first-nbytes"},
-          .type = GF_OPTION_TYPE_SIZET,
-          .min = 0,
-          .max = 1 * GF_UNIT_MB,
-          .default_value = "0",
         },
-        { .key = {"enable-O_SYNC"},
+        { .key = {"trickling-writes"},
           .type = GF_OPTION_TYPE_BOOL,
           .default_value = "on",
         },
-        { .key = {"enable-trickling-writes"},
+        { .key = {"strict-O_DIRECT"},
           .type = GF_OPTION_TYPE_BOOL,
-          .default_value = "on",
+          .default_value = "off",
+        },
+        { .key = {"strict-write-ordering"},
+          .type = GF_OPTION_TYPE_BOOL,
+          .default_value = "off",
+	  .description = "Do not let later writes overtake earlier writes even "
+	                  "if they do not overlap",
         },
         { .key = {NULL} },
 };