nfs: Implement fileattr_get for case sensitivity

An NFS server re-exporting an NFS mount point needs to report
the case sensitivity behavior of the underlying filesystem to
its clients. NFSD's attribute encoder obtains that information
by calling vfs_fileattr_get() on the lower filesystem, so the
NFS client must implement fileattr_get to surface what it
learned from its own server.

The NFS client already retrieves case sensitivity information
from servers during mount via PATHCONF (NFSv3) or the
FATTR4_CASE_INSENSITIVE/FATTR4_CASE_PRESERVING attributes
(NFSv4). Expose this information through fileattr_get by
reporting the FS_XFLAG_CASEFOLD and FS_XFLAG_CASENONPRESERVING
flags. NFSv2 lacks PATHCONF support, so mounts using that protocol
version default to standard POSIX behavior: case-sensitive and
case-preserving.

PATHCONF is now invoked unconditionally for NFSv2 and NFSv3 mounts
so the case-sensitivity capabilities are established even when the
user pins server->namelen with the namlen= mount option. That option
is orthogonal to case handling, and skipping PATHCONF because
namelen was already known would leave the caps unset.

The two capability bits carry opposite polarity because their POSIX
defaults differ. Most servers are case-sensitive and case-
preserving, matching "neither xflag set." NFS_CAP_CASE_INSENSITIVE
is set only when the server affirms case insensitivity, so "server
said no" and "server did not answer" both collapse to the case-
sensitive default. NFS_CAP_CASE_NONPRESERVING follows the same
pattern in the opposite direction: set only when the server affirms
that it does not preserve case, so that silence or a missing
attribute lands on the case-preserving default. The NFSv4 probe
checks res.attr_bitmask[0] to distinguish "server said false" from
"server omitted the attribute" before setting the bit.

Both capability bits are cleared before each probe so a remount,
an NFSv4 transparent state migration to a server with different
case semantics, or a probe whose reply does not arrive does not
retain stale capabilities from the prior probe.

Reviewed-by: Roland Mainz <roland.mainz@nrubsig.org>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Link: https://patch.msgid.link/20260507-case-sensitivity-v14-10-e62cc8200435@oracle.com
Signed-off-by: Christian Brauner <brauner@kernel.org>

0 files changed, 0 insertions, 0 deletions