ceph: do not cache negative dentries for snapped directories

When a LOOKUP/LOOKUPSNAP in a snapped directory returns ENOENT
without a trace, ceph_finish_lookup() creates a negative dentry
via d_add(dentry, NULL).  For live directories this is fine — the
dentry naturally expires.  But for snapped directories,
ceph_d_revalidate() unconditionally trusts all cached dentries
(valid = 1), so a negative dentry created by a transient error
persists forever, hiding entries that genuinely exist in the
snapshot.

Only cache negative dentries for live (non-snapshotted) parent
directories.  For snapped parents, skip the negative dentry so
that VFS retries the lookup on the next access.  Since the
conditions that trigger a negative dentry (MDS transient error,
local ENOENT shortcut, or MDS null dentry lease) are all rare in
snapped directories, the performance impact of this change is
negligible.

Link: https://tracker.ceph.com/issues/78529
Reported-by: Andras Pataki <apataki@flatironinstitute.org>
Signed-off-by: Xiubo Li <xiubo.li@clyso.com>
Reviewed-by: Viacheslav Dubeyko <slava@dubeyko.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

0 files changed, 0 insertions, 0 deletions