features/changelog: RPC'fy {libgf}changelog

This patch introduces RPC based communication between the changelog
translator and libgfchangelog. It replaces the old pathetic stream
based interaction that existed earlier (due to time constraints :-/).

Changelog, upon initialization starts a RPC server (rpcsvc) allowing
clients to invoke a probe API as a bootup mechanism to request for
event notifications. During probe, clients can choose an event
filter specifying the type(s) of events they are interested in. As
of now there is no way to change the event notification set once
the probe RPC call is made, but that is easier to implement.

The actual event notifications is done on a separate RPC session.
The client (libgfchangelog) itself starts and RPC server which the
changelog translator "connects back" during probe. Notifications
are dispatched by a bunch of threads from the server (translator)
and the client optionally orders them if ordered notifications
are requried. FOPs fill in their respective event details in a
buffer (rot-buffs to be particular) and a bunch of threads
(consumers) swap the buffers out of roatation and dispatch them
via RPC. To avoid writer starvation, then number of dispatcher
threads is one less than the number of buffer list in rot-buffs.x

libgfchangelog becomes purely callback based -- upon event
notification from the server (and re-ordering them if required)
invoke a callback routine specified by consumer(s).

A major part of the patch is also aimed at providing backward
compatibility for geo-replication, which was one of the main
consumer of the stream based API. Also, this patch does not\
"turn on" event notifications for all fops, just a bunch which
is currently in requirement. Another pain point is that the
server does not filter events before dispatching it to the
clients. That load is taken up by the client itself (although
it's done at the library layer rather than making it hard on
the callback implementor). This needs improvement and care
needs to be taken to not load the server up with expensive
filtering mechanisms.

Change-Id: Ibf60a432b68f2dfa60c6f9add2bcfd37a9c41395
BUG: 1170075
Signed-off-by: Venky Shankar <vshankar@redhat.com>
Reviewed-on: http://review.gluster.org/9708
Reviewed-by: Jeff Darcy <jdarcy@redhat.com>
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Vijay Bellur <vbellur@redhat.com>

1 files changed, 140 insertions, 0 deletions

diff --git a/xlators/features/changelog/src/changelog-ev-handle.h b/xlators/features/changelog/src/changelog-ev-handle.h
new file mode 100644
index 00000000000..eef0492a9ee
--- /dev/null
+++ b/xlators/features/changelog/src/changelog-ev-handle.h
@@ -0,0 +1,140 @@
+/*
+   Copyright (c) 2015 Red Hat, Inc. <http://www.redhat.com>
+   This file is part of GlusterFS.
+
+   This file is licensed to you under your choice of the GNU Lesser
+   General Public License, version 3 or any later version (LGPLv3 or
+   later), or the GNU General Public License, version 2 (GPLv2), in all
+   cases as published by the Free Software Foundation.
+*/
+
+#ifndef __CHANGELOG_EV_HANDLE_H
+#define __CHANGELOG_EV_HANDLE_H
+
+#include "list.h"
+#include "xlator.h"
+#include "rpc-clnt.h"
+
+#include "rot-buffs.h"
+
+struct changelog_clnt;
+
+typedef struct changelog_rpc_clnt {
+        xlator_t *this;
+
+        gf_lock_t lock;
+
+        unsigned long ref;
+        gf_boolean_t  disconnected;
+
+        unsigned int filter;
+        char sock[UNIX_PATH_MAX];
+
+        struct changelog_clnt *c_clnt;   /* back pointer to list holder */
+
+        struct rpc_clnt *rpc;            /* RPC client endpoint */
+
+        struct list_head list;           /* ->pending, ->waitq, ->active */
+
+        void (*cleanup)
+        (struct changelog_rpc_clnt *);   /* cleanup handler */
+} changelog_rpc_clnt_t;
+
+static inline void
+changelog_rpc_clnt_ref (changelog_rpc_clnt_t *crpc)
+{
+        LOCK (&crpc->lock);
+        {
+                ++crpc->ref;
+        }
+        UNLOCK (&crpc->lock);
+}
+
+static inline void
+changelog_set_disconnect_flag (changelog_rpc_clnt_t *crpc, gf_boolean_t flag)
+{
+        crpc->disconnected = flag;
+}
+
+static inline int
+changelog_rpc_clnt_is_disconnected (changelog_rpc_clnt_t *crpc)
+{
+        return (crpc->disconnected == _gf_true);
+}
+
+static inline void
+changelog_rpc_clnt_unref (changelog_rpc_clnt_t *crpc)
+{
+        gf_boolean_t gone = _gf_false;
+
+        LOCK (&crpc->lock);
+        {
+                if (!(--crpc->ref)
+                    && changelog_rpc_clnt_is_disconnected (crpc)) {
+                        list_del (&crpc->list);
+                        gone = _gf_true;
+                }
+        }
+        UNLOCK (&crpc->lock);
+
+        if (gone)
+                crpc->cleanup (crpc);
+}
+
+/**
+ * This structure holds pending and active clients. On probe RPC all
+ * an instance of the above structure (@changelog_rpc_clnt) is placed
+ * in ->pending and gets moved to ->active on a successful connect.
+ *
+ * locking rules:
+ *
+ * Manipulating ->pending
+ * ->pending_lock
+ *    ->pending
+ *
+ * Manipulating ->active
+ * ->active_lock
+ *    ->active
+ *
+ * Moving object from ->pending to ->active
+ * ->pending_lock
+ *   ->active_lock
+ *
+ * Objects are _never_ moved from ->active to ->pending, i.e., during
+ * disconnection, the object is destroyed. Well, we could have tried
+ * to reconnect, but that's pure waste.. let the other end reconnect.
+ */
+
+typedef struct changelog_clnt {
+        xlator_t *this;
+
+        /* pending connections */
+        pthread_mutex_t pending_lock;
+        pthread_cond_t pending_cond;
+        struct list_head pending;
+
+        /* current active connections */
+        gf_lock_t active_lock;
+        struct list_head active;
+
+        gf_lock_t wait_lock;
+        struct list_head waitq;
+
+        /* consumer part of rot-buffs */
+        rbuf_t *rbuf;
+        unsigned long sequence;
+} changelog_clnt_t;
+
+void *changelog_ev_connector (void *);
+
+void *changelog_ev_dispatch (void *);
+
+/* APIs */
+void
+changelog_ev_queue_connection (changelog_clnt_t *, changelog_rpc_clnt_t *);
+
+void
+changelog_ev_cleanup_connections (xlator_t *, changelog_clnt_t *);
+
+#endif
+