geo-rep: Fix syncing of hardlink of symlink

Problem:
If there is a hardlink to a symlink on master
and if the symlink file is deleted on master,
geo-rep fails to sync the hardlink.

Typical Usecase:
It's easily hit with rsnapshot use case where
it uses hardlinks.

Example Reproducer:
Setup geo-replication between master and slave
volume and in master mount point, do the following.

 1. mkdir /tmp/symlinkbug
 2. ln -f -s /does/not/exist /tmp/symlinkbug/a_symlink
 3. rsync -a /tmp/symlinkbug ./
 4. cp -al symlinkbug symlinkbug.0
 5. ln -f -s /does/not/exist2 /tmp/symlinkbug/a_symlink
 6. rsync -a /tmp/symlinkbug ./
 7. cp -al symlinkbug symlinkbug.1

Cause:
If the source was not present while syncing hardlink,
it was always packing the blob as regular file.

Fix:
If the source was not present while syncing hardlink,
pack the blob based on the mode.

Change-Id: Iaa12d6f99de47b18e0650e7c4eb455f23f8390f2
BUG: 1432046
Signed-off-by: Kotresh HR <khiremat@redhat.com>
Reported-by: Christian Lohmaier <lohmaier+rhbz@gmail.com>
Reviewed-on: https://review.gluster.org/18011
Smoke: Gluster Build System <jenkins@build.gluster.org>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Aravinda VK <avishwan@redhat.com>

1 files changed, 46 insertions, 0 deletions

diff --git a/geo-replication/syncdaemon/syncdutils.py b/geo-replication/syncdaemon/syncdutils.py
index 43b21668a46..2187ecd226b 100644
--- a/geo-replication/syncdaemon/syncdutils.py
+++ b/geo-replication/syncdaemon/syncdutils.py
@@ -66,6 +66,8 @@ except ImportError:
 _CL_AUX_GFID_PFX = ".gfid/"
 GF_OP_RETRIES = 10
 
+GX_GFID_CANONICAL_LEN = 37  # canonical gfid len + '\0'
+
 CHANGELOG_AGENT_SERVER_VERSION = 1.0
 CHANGELOG_AGENT_CLIENT_VERSION = 1.0
 NodeID = None
@@ -371,6 +373,33 @@ class GsyncdError(Exception):
     pass
 
 
+class _MetaXattr(object):
+
+    """singleton class, a lazy wrapper around the
+    libcxattr module
+
+    libcxattr (a heavy import due to ctypes) is
+    loaded only when when the single
+    instance is tried to be used.
+
+    This reduces runtime for those invocations
+    which do not need filesystem manipulation
+    (eg. for config, url parsing)
+    """
+
+    def __getattr__(self, meth):
+        from libcxattr import Xattr as LXattr
+        xmeth = [m for m in dir(LXattr) if m[0] != '_']
+        if meth not in xmeth:
+            return
+        for m in xmeth:
+            setattr(self, m, getattr(LXattr, m))
+        return getattr(self, meth)
+
+
+Xattr = _MetaXattr()
+
+
 def getusername(uid=None):
     if uid is None:
         uid = os.geteuid()
@@ -524,6 +553,23 @@ def lstat(e):
     return errno_wrap(os.lstat, [e], [ENOENT], [ESTALE, EBUSY])
 
 
+def get_gfid_from_mnt(gfidpath):
+    return errno_wrap(Xattr.lgetxattr,
+                      [gfidpath, 'glusterfs.gfid.string',
+                       GX_GFID_CANONICAL_LEN], [ENOENT], [ESTALE])
+
+
+def matching_disk_gfid(gfid, entry):
+    disk_gfid = get_gfid_from_mnt(entry)
+    if isinstance(disk_gfid, int):
+        return False
+
+    if not gfid == disk_gfid:
+        return False
+
+    return True
+
+
 class NoStimeAvailable(Exception):
     pass