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.

> Reviewed-on: https://review.gluster.org/18232
> Reviewed-by: Shreyas Siravara <sshreyas@fb.com>
Fixes gluster/glusterfs#370
Signed-off-by: ShyamsundarR <srangana@redhat.com>
Change-Id: I614a247834fb8f2b2743c0c67d11cefafff0dbaa

4 files changed, 31 insertions, 0 deletions

diff --git a/xlators/mgmt/glusterd/src/glusterd-volume-set.c b/xlators/mgmt/glusterd/src/glusterd-volume-set.c
index 7750914705e..eef95e8809d 100644
--- a/xlators/mgmt/glusterd/src/glusterd-volume-set.c
+++ b/xlators/mgmt/glusterd/src/glusterd-volume-set.c
@@ -2843,6 +2843,11 @@ struct volopt_map_entry glusterd_volopt_map[] = {
           .voltype     = "storage/posix",
           .op_version  = GD_OP_VERSION_4_0_0,
         },
+        { .option      = "max-hardlinks",
+          .key         = "storage.max-hardlinks",
+          .voltype     = "storage/posix",
+          .op_version  = GD_OP_VERSION_4_0_0,
+        },
         { .key         = "storage.bd-aio",
           .voltype     = "storage/bd",
           .op_version  = 3
diff --git a/xlators/storage/posix/src/posix-common.c b/xlators/storage/posix/src/posix-common.c
index 011bef8a720..1b2bb609fb0 100644
--- a/xlators/storage/posix/src/posix-common.c
+++ b/xlators/storage/posix/src/posix-common.c
@@ -398,6 +398,8 @@ posix_reconfigure (xlator_t *this, dict_t *options)
                           options, int32, out);
         priv->create_directory_mask = create_directory_mask;
 
+        GF_OPTION_RECONF ("max-hardlinks", priv->max_hardlinks,
+                          options, uint32, out);
         ret = 0;
 out:
         return ret;
@@ -1075,6 +1077,8 @@ posix_init (xlator_t *this)
         GF_OPTION_INIT ("create-directory-mask",
                         create_directory_mask, int32, out);
         _private->create_directory_mask = create_directory_mask;
+
+        GF_OPTION_INIT ("max-hardlinks", _private->max_hardlinks, uint32, out);
 out:
         if (ret) {
                 if (_private) {
@@ -1322,5 +1326,17 @@ struct volume_options options[] = {
           .description = "Any bit not set here will be removed from the"
           "modes set on a directory when it is created"
         },
+        {
+          .key = {"max-hardlinks"},
+          .type = GF_OPTION_TYPE_INT,
+          .min = 0,
+          .default_value = "100",
+          .op_version  = {GD_OP_VERSION_4_0_0},
+          .flags = OPT_FLAG_SETTABLE | OPT_FLAG_DOC,
+          .tags = {"posix"},
+          .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-entry-ops.c b/xlators/storage/posix/src/posix-entry-ops.c
index 7a83eb3dfba..e7658e46543 100644
--- a/xlators/storage/posix/src/posix-entry-ops.c
+++ b/xlators/storage/posix/src/posix-entry-ops.c
@@ -1814,6 +1814,15 @@ 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;
diff --git a/xlators/storage/posix/src/posix.h b/xlators/storage/posix/src/posix.h
index 36348767870..afb4b4413f6 100644
--- a/xlators/storage/posix/src/posix.h
+++ b/xlators/storage/posix/src/posix.h
@@ -239,6 +239,7 @@ struct posix_private {
         mode_t          force_directory_mode;
         mode_t          create_mask;
         mode_t          create_directory_mask;
+        uint32_t max_hardlinks;
 };
 
 typedef struct {