geo-rep: Fix syncing multiple rename of symlink

Problem:
Geo-rep fails to sync rename of symlink if it's
renamed multiple times if creation and rename
happened successively

Worker crash at slave:
Traceback (most recent call last):
  File "/usr/libexec/glusterfs/python/syncdaemon/repce.py",  in worker
    res = getattr(self.obj, rmeth)(*in_data[2:])
  File "/usr/libexec/glusterfs/python/syncdaemon/resource.py", in entry_ops
    [ESTALE, EINVAL, EBUSY])
  File "/usr/libexec/glusterfs/python/syncdaemon/syncdutils.py", in errno_wrap
    return call(*arg)
  File "/usr/libexec/glusterfs/python/syncdaemon/libcxattr.py", in lsetxattr
    cls.raise_oserr()
  File "/usr/libexec/glusterfs/python/syncdaemon/libcxattr.py", in raise_oserr
    raise OSError(errn, os.strerror(errn))
OSError: [Errno 12] Cannot allocate memory

Geo-rep Behaviour:
1. SYMLINK doesn't record target path in changelog.
   So while syncing SYMLINK, readlink is done on
   master to get target path.

2. Geo-rep will create destination if source is not
   present while syncing RENAME. Hence while syncing
   RENAME of SYMLINK, target path is collected from
   destination.

Cause:
If symlink is created and renamed multiple times, creation of
symlink is ignored, as it's no longer present on master at
that path. While symlink is renamed multiple times at master,
when syncing first RENAME of SYMLINK, both source and destination
is not present, hence target path is not known.  In this case,
while creating destination directly at slave,  regular file
attributes were encoded into blob instead of symlink,
causing failure in gfid-access translator while decoding
blob.

Solution:
While syncing of RENAME of SYMLINK, when target is not known
and when src and destination is not present on the master,
don't create destination. Ignore the rename. It's ok to ignore.
If it's unliked, it's fine.  If it's renamed to something else,
it will be synced then.

Backport of:
> Change-Id: Ibdfa495513b7c05b5370ab0b89c69a6802338d87
> BUG: bz#1693648
> Signed-off-by: Kotresh HR <khiremat@redhat.com>
(cherry picked from commit 877af725b3e35b548d6d7aeec5adb21721d8bf8b)

Change-Id: Ibdfa495513b7c05b5370ab0b89c69a6802338d87
fixes: bz#1694002
Signed-off-by: Kotresh HR <khiremat@redhat.com>
(cherry picked from commit 877af725b3e35b548d6d7aeec5adb21721d8bf8b)

1 files changed, 14 insertions, 9 deletions

diff --git a/geo-replication/syncdaemon/resource.py b/geo-replication/syncdaemon/resource.py
index a2d0b16899a..c290d86880e 100644
--- a/geo-replication/syncdaemon/resource.py
+++ b/geo-replication/syncdaemon/resource.py
@@ -625,15 +625,20 @@ class Server(object):
                 # exist with different gfid.
                 if not matching_disk_gfid(gfid, entry):
                     if e['stat'] and not stat.S_ISDIR(e['stat']['mode']):
-                        if stat.S_ISLNK(e['stat']['mode']) and \
-                           e['link'] is not None:
-                            st1 = lstat(en)
-                            if isinstance(st1, int):
-                                (pg, bname) = entry2pb(en)
-                                blob = entry_pack_symlink(cls, gfid, bname,
-                                                          e['link'], e['stat'])
-                            elif not matching_disk_gfid(gfid, en):
-                                collect_failure(e, EEXIST, uid, gid, True)
+                        if stat.S_ISLNK(e['stat']['mode']):
+                            # src is not present, so don't sync symlink as
+                            # we don't know target. It's ok to ignore. If
+                            # it's unliked, it's fine. If it's renamed to
+                            # something else, it will be synced then.
+                            if e['link'] is not None:
+                                st1 = lstat(en)
+                                if isinstance(st1, int):
+                                    (pg, bname) = entry2pb(en)
+                                    blob = entry_pack_symlink(cls, gfid, bname,
+                                                              e['link'],
+                                                              e['stat'])
+                                elif not matching_disk_gfid(gfid, en):
+                                    collect_failure(e, EEXIST, uid, gid, True)
                         else:
                             slink = os.path.join(pfx, gfid)
                             st = lstat(slink)