NFS: allow close-to-open cache semantics to apply to root of NFS filesystem
To obey NFS cache semantics, the client must verify the cached attributes when a file is opened. In most cases this is done by a call to d_validate as one of the last steps in path_walk. However for the root of a filesystem, d_validate is only ever called on the mounted-on filesystem (except when the path ends '.' or '..'). So NFS has no chance to validate the attributes. So, in nfs_opendir, we revalidate the attributes if the opened directory is the mountpoint. This may cause double-validation for "." and ".." lookups, but that is better than missing regular /path/name lookups completely. Signed-off-by: NeilBrown <neilb@suse.de> Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
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