shared: test for fsync after adding xattrs to a file

shared: test for fsync after adding xattrs to a file

This test is motivated by an issue found in btrfs.

It test that after syncing the filesystem, adding many xattrs to a file,
syncing the filesystem again, writing to the file and then doing a fsync
against that file, all the xattrs still exists after a power failure.
That is, after the fsync log/journal is replayed, the xattrs still exist
and with the correct values.

The btrfs issue is fixed by the patch titled:

  "Btrfs: fix fsync xattr loss in the fast fsync path"

Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>