nfs: persistent caching of connected NFS-clients

Introduce /var/lib/glusterfs/nfs/rmtab to contain a list of NFS-clients
which have a volume mounted. The volume option 'nfs.mount-rmtab' can be
set to an alternative filename. When the file is located on shared
storage, multiple gNFS servers can use the same file to present a single
NFS-server.

This cache is read when a system administrator calls 'showmount -a' and
updated when an NFS-client calls MNT or UMNT from the MOUNT protocol.

Usage:
- create a volume for storing the shared rmtab file
- mount the volume on all storage servers, at the same location
- make sure that the volume is mounted at boot (add to /etc/fstab)
- place the rmtab file on the volume:
   # gluster volume set <VOLUME> nfs.mount-rmtab <MOUNTPOINT>/<FILENAME>
- any subsequent mount requests will add an entry to this file
- 'showmount -a' requests will return the NFS-clients using the cluster

Note:
The NFS-server does currently not support reconfigure(). When a
configuration option is set/changed, the NFS-server glusterfs process
gets restarted. This causes the active NFS-clients to be forgotten (the
entries are saved in the old rmtab, but we do not have a reference to
that file any more, so we can't re-add them). Therefor a re-mount done
by the NFS-clients is needed before they get listed in the rmtab again.

Change-Id: I58f47135d60ad112849d647bea4e1129683dd2b3
BUG: 904065
Signed-off-by: Niels de Vos <ndevos@redhat.com>
Reviewed-on: http://review.gluster.org/4430
Tested-by: Gluster Build System <jenkins@build.gluster.com>
Reviewed-by: Harshavardhana <harsha@harshavardhana.net>
Tested-by: Harshavardhana <harsha@harshavardhana.net>
Reviewed-by: Rajesh Joseph <rjoseph@redhat.com>

1 files changed, 65 insertions, 0 deletions

diff --git a/xlators/nfs/server/src/nfs.c b/xlators/nfs/server/src/nfs.c
index 49512438e..831e82a8c 100644
--- a/xlators/nfs/server/src/nfs.c
+++ b/xlators/nfs/server/src/nfs.c
@@ -51,6 +51,10 @@
 #define OPT_SERVER_AUX_GIDS             "nfs.server-aux-gids"
 #define OPT_SERVER_GID_CACHE_TIMEOUT    "nfs.server.aux-gid-timeout"
 
+/* TODO: DATADIR should be based on configure's $(localstatedir) */
+#define DATADIR                         "/var/lib/glusterd"
+#define NFS_DATADIR                     DATADIR "/nfs"
+
 /* Every NFS version must call this function with the init function
  * for its particular version.
  */
@@ -696,6 +700,15 @@ nfs_init_state (xlator_t *this)
                         nfs->mount_udp = 1;
         }
 
+        nfs->rmtab = NFS_DATADIR "/rmtab";
+        if (dict_get(this->options, "nfs.mount-rmtab")) {
+                ret = dict_get_str (this->options, "nfs.mount-rmtab", &nfs->rmtab);
+                if (ret == -1) {
+                        gf_log (GF_NFS, GF_LOG_ERROR, "Failed to parse dict");
+                        goto free_foppool;
+                }
+        }
+
         /* support both options rpc-auth.ports.insecure and
          * rpc-auth-allow-insecure for backward compatibility
          */
@@ -816,6 +829,49 @@ nfs_drc_init (xlator_t *this)
         return ret;
 }
 
+
+#if 0
+/* reconfigure() is currently not used for the NFS-server. Upon setting an
+ * option for the NFS-xlator, the glusterfs process it restarted.
+ *
+ * This current implementation makes sure to read the currently used rmtab and
+ * merge it with the new rmtab.
+ *
+ * As this function is never called, it is provided for the future, for when
+ * the NFS-server supports reloading.
+ */
+int
+reconfigure (xlator_t *this, dict_t *options)
+{
+        int                       ret = 0;
+        char                     *rmtab = NULL;
+        struct nfs_state         *nfs = NULL;
+
+        nfs = (struct nfs_state *)this->private;
+
+        if (!nfs) {
+                gf_log_callingfn (this->name, GF_LOG_DEBUG, "conf == null!!!");
+                goto out;
+        }
+
+        ret = dict_get_str (options, "nfs.mount-rmtab", &rmtab);
+        if (ret) {
+                goto out;
+        }
+        gf_path_strip_trailing_slashes (rmtab);
+
+        if (strcmp (nfs->rmtab, rmtab) != 0) {
+                mount_rewrite_rmtab (nfs->mstate, rmtab);
+
+                gf_log (this->name, GF_LOG_INFO,
+                        "Reconfigured nfs.mount-rmtab path: %s", nfs->rmtab);
+        }
+
+out:
+        return ret;
+}
+#endif /* glusterfs/nfs is restarted and reconfigure() is never called */
+
 int
 init (xlator_t *this) {
 
@@ -1337,6 +1393,15 @@ struct volume_options options[] = {
                          "The need for enabling this option often depends "
                          "on the usage of NLM."
         },
+        { .key = {"nfs.mount-rmtab"},
+          .type = GF_OPTION_TYPE_PATH,
+          .default_value = DATADIR "/rmtab",
+          .description = "Set the location of the cache file that is used to "
+                         "list all the NFS-clients that have connected "
+                         "through the MOUNT protocol. If this is on shared "
+                         "storage, all GlusterFS servers will update and "
+                         "output (with 'showmount') the same list."
+        },
         { .key = {OPT_SERVER_AUX_GIDS},
           .type = GF_OPTION_TYPE_BOOL,
           .default_value = "off",