storage/posix: Add limit to number of hard links.

Summary:
Too may hard links blow up btrfs by exceeding max xattr size (recordign
pgfid for each hardlink). Add a limit to prevent this explosion.

This is a port D4682329 to 3.8

Reviewed By: sshreyas

Change-Id: I614a247834fb8f2b2743c0c67d11cefafff0dbaa
Reviewed-on: https://review.gluster.org/18232
Reviewed-by: Shreyas Siravara <sshreyas@fb.com>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Smoke: Gluster Build System <jenkins@build.gluster.org>

4 files changed, 77 insertions, 2 deletions

diff --git a/tests/basic/hardlink-limit.t b/tests/basic/hardlink-limit.t
new file mode 100644
index 00000000000..e90a3ce427c
--- /dev/null
+++ b/tests/basic/hardlink-limit.t
@@ -0,0 +1,44 @@
+#!/bin/bash
+
+. $(dirname $0)/../include.rc
+. $(dirname $0)/../volume.rc
+. $(dirname $0)/../dht.rc
+
+cleanup;
+
+TEST glusterd
+TEST pidof glusterd
+TEST $CLI volume info;
+
+TEST $CLI volume create $V0 replica 2  $H0:$B0/${V0}{1,2,3,4};
+
+EXPECT "$V0" volinfo_field $V0 'Volume Name';
+EXPECT 'Created' volinfo_field $V0 'Status';
+EXPECT '4' brick_count $V0
+
+TEST $CLI volume start $V0;
+EXPECT 'Started' volinfo_field $V0 'Status';
+TEST $CLI volume set $V0 storage.max-hardlinks 3
+TEST glusterfs -s $H0 --volfile-id $V0 $M0;
+
+TEST dd if=/dev/zero of=$M0/testfile count=1
+
+# max-hardlinks is 3, should be able to create 2 links.
+TEST link $M0/testfile $M0/testfile.link1
+TEST link $M0/testfile $M0/testfile.link2
+
+# But not 3.
+TEST ! link $M0/testfile $M0/testfile.link3
+# If we remove one...
+TEST rm $M0/testfile.link1
+# Now we can add one.
+TEST link $M0/testfile $M0/testfile.link3
+
+# But not another
+TEST ! link $M0/testfile $M0/testfile.link4
+
+# Unless we disable the limit...
+TEST $CLI volume set $V0 storage.max-hardlinks 0
+TEST link $M0/testfile $M0/testfile.link4
+
+cleanup;
diff --git a/xlators/mgmt/glusterd/src/glusterd-volume-set.c b/xlators/mgmt/glusterd/src/glusterd-volume-set.c
index a4a0096d17d..7345dd714d3 100644
--- a/xlators/mgmt/glusterd/src/glusterd-volume-set.c
+++ b/xlators/mgmt/glusterd/src/glusterd-volume-set.c
@@ -2579,6 +2579,10 @@ struct volopt_map_entry glusterd_volopt_map[] = {
           .voltype     = "storage/posix",
           .op_version  = 2,
         },
+        { .key         = "storage.max-hardlinks",
+          .voltype     = "storage/posix",
+          .op_version  = 2,
+        },
         { .key         = "storage.bd-aio",
           .voltype     = "storage/bd",
           .op_version  = 3
diff --git a/xlators/storage/posix/src/posix.c b/xlators/storage/posix/src/posix.c
index 4105bff323f..d4b8effd6da 100644
--- a/xlators/storage/posix/src/posix.c
+++ b/xlators/storage/posix/src/posix.c
@@ -2785,6 +2785,16 @@ posix_link (call_frame_t *frame, xlator_t *this,
                 goto out;
         }
 
+        if (priv->max_hardlinks && stbuf.ia_nlink >= priv->max_hardlinks) {
+                op_ret = -1;
+                op_errno = EMLINK;
+                gf_log (this->name, GF_LOG_ERROR,
+                        "hardlink failed: %s exceeds max link count (%u/%u).",
+                        real_oldpath, stbuf.ia_nlink, priv->max_hardlinks);
+                goto out;
+        }
+
+
         MAKE_ENTRY_HANDLE (real_newpath, par_newpath, this, newloc, &stbuf);
         if (!real_newpath || !par_newpath) {
                 op_ret = -1;
@@ -6883,7 +6893,13 @@ struct posix_private *priv = NULL;
         }
         pthread_mutex_unlock (&priv->freespace_check_lock);
 
-	ret = 0;
+        GF_OPTION_RECONF ("fadvise-random", priv->fadvise_random,
+                          options, bool, out);
+
+        GF_OPTION_RECONF ("max-hardlinks", priv->max_hardlinks,
+                          options, uint32, out);
+
+        ret = 0;
 out:
 	return ret;
 }
@@ -7506,6 +7522,8 @@ init (xlator_t *this)
 
         GF_OPTION_INIT ("fadvise-random", _private->fadvise_random, bool, out);
 
+        GF_OPTION_INIT ("max-hardlinks", _private->max_hardlinks, uint32, out);
+
         pthread_mutex_init (&_private->freespace_check_lock, NULL);
         sys_statvfs (_private->base_path, &_private->freespace_stats);
         clock_gettime (CLOCK_MONOTONIC, &_private->freespace_check_last);
@@ -7712,6 +7730,14 @@ struct volume_options options[] = {
           .description = "fadvise fd's with POSIX_FADV_RANDOM to bypass "
                          "read-ahead limits",
         },
-
+        {
+          .key = {"max-hardlinks"},
+          .type = GF_OPTION_TYPE_INT,
+          .min = 0,
+          .default_value = "100",
+          .validate = GF_OPT_VALIDATE_MIN,
+          .description = "max number of hardlinks allowed on any one inode.\n"
+                         "0 is unlimited, 1 prevents any hardlinking at all."
+        },
         { .key  = {NULL} }
 };
diff --git a/xlators/storage/posix/src/posix.h b/xlators/storage/posix/src/posix.h
index 6dde604cc0c..794f06c8ada 100644
--- a/xlators/storage/posix/src/posix.h
+++ b/xlators/storage/posix/src/posix.h
@@ -183,6 +183,7 @@ struct posix_private {
         uint32_t freespace_check_interval;
         gf_boolean_t freespace_check_passed;
         gf_boolean_t fadvise_random;
+        uint32_t max_hardlinks;
 };
 
 typedef struct {