fuse: introduce pre-test micro-framework, check for execve-over-direct-IO

The presence of some potential FUSE features in the actual kernel-side FUSE
implementation we run on is not always straightforward. More precisely, it is
straightforward only if there is a dedicated feature flag or protocol revision
number. In the other cases we are left to clumsy and platform specific hacks
which wire in 3rd-party software revision numbers into our source... at least,
if we insist on sticking to (the otherwise venerable) KISS principle.

However, here we go for another route, loosely inspired by the way autotools
provide an abstraction layer for our build system over the gory details of
platform specific build environments.

At start time, we use a preliminary set of FUSE operations which overlay the
standard ones such that apart from the "usual stuff", they also present some
synthetic files to the FUSE client (kernel). Then we spawn some test programs
which perform the needed tests on these synthetic files to evaulate the FUSE
implementation in terms of the features in question. According to the result
of the test programs, we set the respective parameters of the fuse xlator;
when the testing phase is over, the FUSE operation set is replaced by the
standard one.

As of now, we use this approach to test whether execve(2) works with
direct I/O. If yes, and if glusterfs is used with --enable-direct-io-mode,
then we let direct I/O for files opened for reading; if no, then we restrict
direct I/O only to writing files.

Signed-off-by: Csaba Henk <csaba@gluster.com>
Signed-off-by: Vijay Bellur <vijay@dev.gluster.com>

BUG: 801 (Direct io-mode support and related changes in caching translators.)
URL: http://bugs.gluster.com/cgi-bin/bugzilla3/show_bug.cgi?id=801

2 files changed, 333 insertions, 6 deletions

diff --git a/xlators/mount/fuse/src/fuse-bridge.c b/xlators/mount/fuse/src/fuse-bridge.c
index aea0f88b0..e37d2e0c8 100644
--- a/xlators/mount/fuse/src/fuse-bridge.c
+++ b/xlators/mount/fuse/src/fuse-bridge.c
@@ -29,6 +29,7 @@
 
 static int gf_fuse_conn_err_log;
 static int gf_fuse_xattr_enotsup_log;
+static int gf_fuse_pre_stuck_log;
 
 
 /*
@@ -536,7 +537,18 @@ fuse_fd_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
                 foo.open_flags = 0;
 
                 if (!IA_ISDIR (fd->inode->ia_type)) {
-                        if (priv->direct_io_mode)
+                        if (priv->direct_io_mode &&
+                            (
+#ifdef GF_LINUX_HOST_OS
+                             (state->flags & O_ACCMODE) != O_RDONLY ||
+#endif
+#ifdef GF_DARWIN_HOST_OS
+                             /* On Darwin machines, O_APPEND is not handled,
+                              * which may corrupt the data
+                              */
+                             (state->flags & O_ACCMODE) == O_RDONLY &&
+#endif
+                             priv->can_exec_directio))
                                 foo.open_flags |= FOPEN_DIRECT_IO;
 #ifdef GF_DARWIN_HOST_OS
                                 /* In Linux: by default, buffer cache
@@ -1430,7 +1442,15 @@ fuse_create_cbk (call_frame_t *frame, void *cookie, xlator_t *this,
         if (op_ret >= 0) {
                 foo.fh = (uintptr_t) fd;
 
-                if (priv->direct_io_mode)
+                if (priv->direct_io_mode &&
+                    (
+#ifdef GF_LINUX_HOST_OS
+                     (state->flags & O_ACCMODE) != O_RDONLY ||
+#endif
+#ifdef GF_DARWIN_HOST_OS
+                     (state->flags & O_ACCMODE) == O_RDONLY &&
+#endif
+                     priv->can_exec_directio))
                         foo.open_flags |= FOPEN_DIRECT_IO;
 
                 gf_log ("glusterfs-fuse", GF_LOG_TRACE,
@@ -2798,6 +2818,9 @@ fuse_setlk (xlator_t *this, fuse_in_header_t *finh, void *msg)
         return;
 }
 
+
+static void *fuse_pre_test_directio_exec (void *arg);
+
 static void
 fuse_init (xlator_t *this, fuse_in_header_t *finh, void *msg)
 {
@@ -2806,6 +2829,9 @@ fuse_init (xlator_t *this, fuse_in_header_t *finh, void *msg)
         struct fuse_init_out fino;
         fuse_private_t *priv = NULL;
         int ret;
+#ifndef GF_DARWIN_HOST_OS
+        pthread_t prethread = {0, };
+#endif
 
         priv = this->private;
 
@@ -2867,6 +2893,20 @@ fuse_init (xlator_t *this, fuse_in_header_t *finh, void *msg)
 
  out:
         GF_FREE (finh);
+
+#ifdef GF_DARWIN_HOST_OS
+        /* MacFUSE applies a "mount comes after a succesful handshake"
+         * strategy, which was taken from early fuse4bsd. Linux (and recent
+         * fuse4bsd) is rather doing "mount, then handshake; if that fails,
+         * unmount" strategy. Therefore on OS X it would be too early to
+         * launch the pre-test thread here. To work this around, we launch
+         * it from the LOOKUP pre-test handler (that will come instantly,
+         * as OS X automatically checks for the presence of some files
+         * upon a new mount).
+         */
+#else
+        pthread_create (&prethread, NULL, &fuse_pre_test_directio_exec, this);
+#endif
 }
 
 
@@ -3035,11 +3075,9 @@ fuse_thread_proc (void *data)
         struct iovec iov_in[2];
         void *msg = NULL;
         const size_t msg0_size = sizeof (*finh) + 128;
-        fuse_handler_t **fuse_ops = NULL;
 
         this = data;
         priv = this->private;
-        fuse_ops = priv->fuse_ops;
 
         THIS = this;
 
@@ -3154,7 +3192,7 @@ fuse_thread_proc (void *data)
                         fuse_enosys (this, finh, msg);
                 else
 #endif
-                fuse_ops[finh->opcode] (this, finh, msg);
+                priv->fuse_ops[finh->opcode] (this, finh, msg);
 
                 iobuf_unref (iobuf);
                 continue;
@@ -3419,6 +3457,287 @@ fuse_dumper (xlator_t *this, fuse_in_header_t *finh, void *msg)
 }
 
 
+/*
+ *  FUSE pre-test stuff
+ *  -------------------
+ */
+
+#define FUSE_PRE_TESTFILE     ".__fuse_pre_testfile"
+#define FUSE_PRE_TESTFILE1    ".__fuse_pre_testfile1"
+#define FUSE_PRE_TESTFILE_ID  ((uint64_t)-1)
+#define FUSE_PRE_TESTFILE_FH  ((uint64_t)1)
+
+#define FUSE_PRE_TEST_TEST do {                                 \
+        if (finh->uid != getuid () ||                           \
+            finh->nodeid != FUSE_PRE_TESTFILE_ID)               \
+                return fuse_std_fallback (this, finh, msg);     \
+} while (0)
+
+static fuse_handler_t *fuse_std_ops[];
+
+static void
+fuse_std_fallback (xlator_t *this, fuse_in_header_t *finh, void *msg)
+{
+        static int fuse_pre_cnt;
+
+        if (fuse_pre_cnt++ > 200)
+                GF_LOG_OCCASIONALLY (gf_fuse_pre_stuck_log,
+                                     "glusterfs-fuse",
+                                     GF_LOG_WARNING,
+                                     "fuse pre test does not complete");
+
+        return fuse_std_ops[finh->opcode] (this, finh, msg);
+}
+
+
+static void
+fuse_pre_lookup (xlator_t *this, fuse_in_header_t *finh, void *msg)
+{
+        char *name = msg;
+        fuse_private_t *priv = NULL;
+        struct fuse_entry_out feo = {0, };
+        unsigned pre_testfile[2] = {0, 0};
+#ifdef GF_DARWIN_HOST_OS
+        static int prethread_spawn;
+        pthread_t prethread = {0, };
+
+        if (!prethread_spawn) {
+                prethread_spawn = 1;
+                pthread_create (&prethread, NULL, &fuse_pre_test_directio_exec,
+                                this);
+        }
+#endif
+
+        priv = this->private;
+
+        pre_testfile[0] = !strcmp (name, FUSE_PRE_TESTFILE);
+        pre_testfile[1] = !strcmp (name, FUSE_PRE_TESTFILE1);
+        if (finh->uid != getuid () ||
+            finh->nodeid != 1 ||
+            !(pre_testfile[0] || pre_testfile[1]))
+                return fuse_std_fallback (this, finh, msg);
+
+        if (priv->pre_test_stage == 0 && pre_testfile[1]) {
+                send_fuse_err (this, finh, ENOENT);
+
+                return;
+        }
+
+        memset (&feo, 0, sizeof (feo));
+        feo.nodeid = FUSE_PRE_TESTFILE_ID;
+        feo.attr.ino = FUSE_PRE_TESTFILE_ID;
+        feo.attr.mode = (priv->pre_test_stage == 2 ? S_IFDIR : S_IFREG) | 0755;
+        feo.attr.nlink = 1;
+
+#if FUSE_KERNEL_MINOR_VERSION >= 9
+        priv->proto_minor >= 9 ?
+        send_fuse_obj (this, finh, &feo) :
+        send_fuse_data (this, finh, &feo,
+                        FUSE_COMPAT_ENTRY_OUT_SIZE);
+#else
+        send_fuse_obj (this, finh, &feo);
+#endif
+}
+
+
+static void
+fuse_pre_getattr (xlator_t *this, fuse_in_header_t *finh, void *msg)
+{
+        fuse_private_t *priv = NULL;
+        struct fuse_attr_out fao = {0, };
+
+        priv = this->private;
+
+        FUSE_PRE_TEST_TEST;
+
+        fao.attr.mode = (priv->pre_test_stage == 2 ? S_IFDIR : S_IFREG) | 0755;
+        fao.attr.nlink = 1;
+
+#if FUSE_KERNEL_MINOR_VERSION >= 9
+        priv->proto_minor >= 9 ?
+        send_fuse_obj (this, finh, &fao) :
+        send_fuse_data (this, finh, &fao,
+                        FUSE_COMPAT_ATTR_OUT_SIZE);
+#else
+        send_fuse_obj (this, finh, &fao);
+#endif
+}
+
+
+static void
+fuse_pre_open (xlator_t *this, fuse_in_header_t *finh, void *msg)
+{
+        struct fuse_open_out   foo = {0, };
+
+        FUSE_PRE_TEST_TEST;
+
+        foo.fh = FUSE_PRE_TESTFILE_FH;
+        foo.open_flags = FOPEN_DIRECT_IO;
+
+        send_fuse_obj (this, finh, &foo);
+}
+
+
+static void
+fuse_pre_deadpan (xlator_t *this, fuse_in_header_t *finh, void *msg)
+{
+        FUSE_PRE_TEST_TEST;
+
+        send_fuse_err (this, finh, 0);
+}
+
+
+static void
+fuse_pre_rename (xlator_t *this, fuse_in_header_t *finh, void *msg)
+{
+        struct fuse_rename_in  *fri = msg;
+        char *oldname = (char *)(fri + 1);
+        char *newname = oldname + strlen (oldname) + 1;
+
+        fuse_private_t *priv = NULL;
+
+        if (finh->uid != getuid () ||
+            finh->nodeid != 1 ||
+            fri->newdir != 1 ||
+            strcmp (oldname, FUSE_PRE_TESTFILE) != 0 ||
+            strcmp (newname, FUSE_PRE_TESTFILE1) != 0)
+                return fuse_std_fallback (this, finh, msg);
+
+        priv = this->private;
+        priv->pre_test_stage = 1;
+
+        send_fuse_err (this, finh, 0);
+}
+
+
+static void
+fuse_pre_release (xlator_t *this, fuse_in_header_t *finh, void *msg)
+{
+        if (finh->nodeid != FUSE_PRE_TESTFILE_ID)
+                return fuse_std_fallback (this, finh, msg);
+
+        send_fuse_err (this, finh, 0);
+}
+
+
+static void
+fuse_pre_forget (xlator_t *this, fuse_in_header_t *finh, void *msg)
+{
+        fuse_private_t *priv = NULL;
+
+        if (finh->nodeid != FUSE_PRE_TESTFILE_ID)
+                return fuse_std_fallback (this, finh, msg);
+
+        gf_log ("glusterfs-fuse", GF_LOG_DEBUG,
+                "terminating pre-test, switching to standard ops");
+        priv = this->private;
+        *(priv->fuse_ops_flipped) = fuse_std_ops;
+}
+
+
+/* XXX  Hope this will work out with xattr based ACL systems... */
+static void
+fuse_pre_xattr (xlator_t *this, fuse_in_header_t *finh, void *msg)
+{
+        FUSE_PRE_TEST_TEST;
+
+        send_fuse_err (this, finh, ENODATA);
+}
+
+
+static fuse_handler_t *fuse_pre_ops[FUSE_OP_HIGH] = {
+        [FUSE_LOOKUP]      = fuse_pre_lookup,
+        [FUSE_FORGET]      = fuse_pre_forget,
+        [FUSE_GETATTR]     = fuse_pre_getattr,
+        [FUSE_ACCESS]      = fuse_pre_deadpan,
+        [FUSE_RENAME]      = fuse_pre_rename,
+        [FUSE_OPEN]        = fuse_pre_open,
+        [FUSE_READ]        = fuse_pre_deadpan,
+        [FUSE_FLUSH]       = fuse_pre_deadpan,
+        [FUSE_RELEASE]     = fuse_pre_release,
+        [FUSE_FSYNC]       = fuse_pre_deadpan,
+        [FUSE_GETXATTR]    = fuse_pre_xattr,
+        [FUSE_LISTXATTR]   = fuse_pre_xattr,
+};
+
+
+enum {
+        FUSE_DIOEXEC_OK,
+        FUSE_DIOEXEC_FAIL,
+        FUSE_DIOEXEC_DUNNO
+};
+
+static void *
+fuse_pre_test_directio_exec (void *arg)
+{
+        fuse_private_t *priv = NULL;
+        pid_t pid = 0;
+        struct stat st = {0, };
+        char pre_testfile[PATH_MAX];
+        char pre_testfile1[PATH_MAX];
+        int ret = 0;
+        xlator_t *this = NULL;
+
+        this = arg;
+        priv = this->private;
+
+        if (fstat (priv->fd, &st) == -1)
+                return NULL;
+        if (strlen (priv->mount_point) +
+            max (strlen (FUSE_PRE_TESTFILE), strlen (FUSE_PRE_TESTFILE1)) + 2 >
+              PATH_MAX)
+                return NULL;
+        strcat (strcat (strcpy (pre_testfile, priv->mount_point), "/"),
+                FUSE_PRE_TESTFILE);
+        strcat (strcat (strcpy (pre_testfile1, priv->mount_point), "/"),
+                FUSE_PRE_TESTFILE1);
+
+        if ((pid = fork ()) == -1)
+                return NULL;
+        if (pid == 0) {
+                close (priv->fd);
+                execl (pre_testfile, FUSE_PRE_TESTFILE, NULL);
+                switch (errno) {
+                case ENOEXEC:
+                        exit (FUSE_DIOEXEC_OK);
+                case EFAULT:
+                        exit (FUSE_DIOEXEC_FAIL);
+                default:
+                        fprintf (stderr,
+                                 "warning: fuse exec-on-diretio pre-test ended"
+                                 " unexpectedly (%s)\n", strerror (errno));
+                        exit (FUSE_DIOEXEC_DUNNO);
+                }
+        }
+
+        if (waitpid (pid, &ret, 0) == pid &&
+            WIFEXITED (ret)) {
+                switch (WEXITSTATUS (ret)) {
+                case FUSE_DIOEXEC_OK:
+                        gf_log ("glusterfs-fuse", GF_LOG_DEBUG,
+                                "exec on directio: OK");
+                        priv->can_exec_directio = 1;
+                        break;
+                case FUSE_DIOEXEC_FAIL:
+                        gf_log ("glusterfs-fuse", GF_LOG_DEBUG,
+                                "exec on directio: FAIL");
+                        break;
+                default:
+                        gf_log ("glusterfs-fuse", GF_LOG_WARNING,
+                                "exec on directio: uninterpretable result");
+                }
+        } else
+                gf_log ("glusterfs-fuse", GF_LOG_WARNING,
+                        "exec on directio: abnormal termination");
+
+        ret = rename (pre_testfile, pre_testfile1);
+        priv->pre_test_stage = 2;
+        stat (ret ? pre_testfile : pre_testfile1, &st);
+
+        pthread_exit (0);
+}
+
+
 int
 init (xlator_t *this_xl)
 {
@@ -3587,11 +3906,15 @@ init (xlator_t *this_xl)
                         fuse_std_ops[i] = fuse_enosys;
                 if (!fuse_dump_ops[i])
                         fuse_dump_ops[i] = fuse_dumper;
+                if (!fuse_pre_ops[i])
+                        fuse_pre_ops[i] = fuse_std_fallback;
         }
-        priv->fuse_ops = fuse_std_ops;
+        priv->fuse_ops = fuse_pre_ops;
+        priv->fuse_ops_flipped = &priv->fuse_ops;
         if (priv->fuse_dump_fd != -1) {
                 priv->fuse_ops0 = priv->fuse_ops;
                 priv->fuse_ops  = fuse_dump_ops;
+                priv->fuse_ops_flipped = &priv->fuse_ops0;
         }
 
         return 0;
diff --git a/xlators/mount/fuse/src/fuse-bridge.h b/xlators/mount/fuse/src/fuse-bridge.h
index 547cc8952..4929252e1 100644
--- a/xlators/mount/fuse/src/fuse-bridge.h
+++ b/xlators/mount/fuse/src/fuse-bridge.h
@@ -27,6 +27,7 @@
 #include <dirent.h>
 #include <sys/mount.h>
 #include <sys/time.h>
+#include <sys/wait.h>
 #include <fnmatch.h>
 
 #ifndef _CONFIG_H
@@ -85,6 +86,7 @@ struct fuse_private {
         char                 fuse_thread_started;
 
         uint32_t             direct_io_mode;
+        char                 can_exec_directio;
         size_t              *msg0_len_p;
 
         double               entry_timeout;
@@ -100,8 +102,10 @@ struct fuse_private {
 
         fuse_handler_t     **fuse_ops;
         fuse_handler_t     **fuse_ops0;
+        fuse_handler_t    ***fuse_ops_flipped;
         pthread_mutex_t      fuse_dump_mutex;
         int                  fuse_dump_fd;
+        char                 pre_test_stage;
 
         glusterfs_graph_t   *next_graph;
         xlator_t            *active_subvol;