client: introduce a new flag indicating if dentries in directory are sorted

When creating a file, Client::insert_dentry_inode() set the dentry's offset
based on directory's max offset. The offset does not reflect the real
postion of the dentry in directory. Later readdir reply from real postion
of the dentry in directory. Later readdir reply from MDS may change the
dentry's position/offset. This inconsistency can cause missing/duplicate
entries in readdir result if readdir is partly satisfied by dcache_readdir().

The fix is introduce a new flag indicating if dentries in directory are
sorted. We use _readdir_cache_cb() to handle readdir only when the flag is
set, clear the flag after creating/deleting/renaming file.

Fixes: #9178
Signed-off-by: Yan, Zheng <zyan@redhat.com>
(cherry picked from commit 600af25493947871c38214aa370e2544a7fea399)
client: preserve ordering of readdir result in cache

Preserve ordering of readdir result in a list, so that the result of cached
readdir is consistant with uncached readdir.

As a side effect, this commit also removes the code that removes stale dentries.
This is OK because stale dentries does not have valid lease, they will be
filter out by the shared gen check in Client::_readdir_cache_cb()

Signed-off-by: Yan, Zheng <zyan@redhat.com>
(cherry picked from commit 346c06c1647658768e927a47768a0bc74de17b53)
client: fix I_COMPLETE_ORDERED checking

Current code marks a directory inode as complete and ordered when readdir
finishes, but it does not check if the directory was modified in the middle
of readdir. This is wrong, directory inode should not be marked as ordered
if it was modified during readddir

The fix is introduce a new counter to the inode data struct, we increase
the counter each time the directory is modified. When readdir finishes, we
check the counter to decide if the directory should be marked as ordered.

Fixes: #9894
Signed-off-by: Yan, Zheng <zyan@redhat.com>
(cherry picked from commit a4caed8a53d011b214ab516090676641f7c4699d)
Merge pull request #2876 from ceph/giant-readdir-fix

Giant readdir fix