linux-toradex.git/Documentation/filesystems/nfs, branch master

NFSD: Sign filehandles

2026-03-30T01:25:09+00:00

NFS clients may bypass restrictive directory permissions by using
open_by_handle() (or other available OS system call) to guess the
filehandles for files below that directory.

In order to harden knfsd servers against this attack, create a method to
sign and verify filehandles using SipHash-2-4 as a MAC (Message
Authentication Code).  According to
https://cr.yp.to/siphash/siphash-20120918.pdf, SipHash can be used as a
MAC, and our use of SipHash-2-4 provides a low 1 in 2^64 chance of forgery.

Filehandles that have been signed cannot be tampered with, nor can
clients reasonably guess correct filehandles and hashes that may exist in
parts of the filesystem they cannot access due to directory permissions.

Append the 8 byte SipHash to encoded filehandles for exports that have set
the "sign_fh" export option.  Filehandles received from clients are
verified by comparing the appended hash to the expected hash.  If the MAC
does not match the server responds with NFS error _STALE.  If unsigned
filehandles are received for an export with "sign_fh" they are rejected
with NFS error _STALE.

Signed-off-by: Benjamin Coddington 
Reviewed-by: Jeff Layton 
Signed-off-by: Chuck Lever

docs: exportfs: Use source code struct documentation

2026-01-14T15:50:37+00:00

Instead of duplicating struct export_operations documentation in both
ReST file and in the C source code, just use the kernel-doc in the docs.

While here, make the sentence preceding the paragraph less redundant.

Signed-off-by: André Almeida 
Link: https://patch.msgid.link/20260112-tonyk-fs_uuid-v1-4-acc1889de772@igalia.com
Reviewed-by: Chuck Lever 
Signed-off-by: Christian Brauner

NFSD: nfsd-io-modes: Separate lists

2025-12-03T14:05:14+00:00

Sphinx reports htmldocs indentation warnings:

Documentation/filesystems/nfs/nfsd-io-modes.rst:58: ERROR: Unexpected indentation. [docutils]
Documentation/filesystems/nfs/nfsd-io-modes.rst:59: WARNING: Block quote ends without a blank line; unexpected unindent. [docutils]

These caused the lists to be shown as long running paragraphs merged
with their previous paragraphs.

Fix these by separating the lists with a blank line.

Fixes: fa8d4e6784d1b6 ("NFSD: add Documentation/filesystems/nfs/nfsd-io-modes.rst")
Reported-by: Stephen Rothwell 
Closes: https://lore.kernel.org/linux-next/20251202152506.7a2d2d41@canb.auug.org.au/
Signed-off-by: Bagas Sanjaya 
Reviewed-by: Jeff Layton 
Reviewed-by: Randy Dunlap 
Tested-by: Randy Dunlap 
Signed-off-by: Chuck Lever

NFSD: nfsd-io-modes: Wrap shell snippets in literal code blocks

2025-12-03T14:05:14+00:00

Sphinx reports htmldocs indentation warnings:

Documentation/filesystems/nfs/nfsd-io-modes.rst:29: ERROR: Unexpected indentation. [docutils]
Documentation/filesystems/nfs/nfsd-io-modes.rst:34: ERROR: Unexpected indentation. [docutils]

Fix these by wrapping shell snippets in literal code blocks.

Fixes: fa8d4e6784d1b6 ("NFSD: add Documentation/filesystems/nfs/nfsd-io-modes.rst")
Reported-by: Stephen Rothwell 
Closes: https://lore.kernel.org/linux-next/20251202152506.7a2d2d41@canb.auug.org.au/
Signed-off-by: Bagas Sanjaya 
Reviewed-by: Jeff Layton 
Reviewed-by: Randy Dunlap 
Tested-by: Randy Dunlap 
Signed-off-by: Chuck Lever

NFSD: Add toctree entry for NFSD IO modes docs

2025-12-03T14:05:14+00:00

Commit fa8d4e6784d1b6 ("NFSD: add
Documentation/filesystems/nfs/nfsd-io-modes.rst") adds documentation for
NFSD I/O modes, but it forgets to add toctree entry for it. Hence,
Sphinx reports:

Documentation/filesystems/nfs/nfsd-io-modes.rst: WARNING: document isn't included in any toctree [toc.not_included]

Add the entry.

Fixes: fa8d4e6784d1b6 ("NFSD: add Documentation/filesystems/nfs/nfsd-io-modes.rst")
Reported-by: Stephen Rothwell 
Closes: https://lore.kernel.org/linux-next/20251202152506.7a2d2d41@canb.auug.org.au/
Signed-off-by: Bagas Sanjaya 
Reviewed-by: Jeff Layton 
Reviewed-by: Randy Dunlap 
Tested-by: Randy Dunlap 
Signed-off-by: Chuck Lever

NFSD: add Documentation/filesystems/nfs/nfsd-io-modes.rst

2025-12-01T14:57:10+00:00

This document details the NFSD IO modes that are configurable using
NFSD's experimental debugfs interfaces:

  /sys/kernel/debug/nfsd/io_cache_read
  /sys/kernel/debug/nfsd/io_cache_write

This document will evolve as NFSD's interfaces do (e.g. if/when NFSD's
debugfs interfaces are replaced with per-export controls).

Future updates will provide more specific guidance and howto
information to help others use and evaluate NFSD's IO modes:
BUFFERED, DONTCACHE and DIRECT.

Signed-off-by: Mike Snitzer 
Signed-off-by: Chuck Lever

NFS: nfsd-maintainer-entry-profile: Inline function name prefixes

2025-11-17T13:46:06+00:00

Sphinx reports htmldocs warnings:

Documentation/filesystems/nfs/nfsd-maintainer-entry-profile.rst:185: ERROR: Unknown target name: "nfsd". [docutils]
Documentation/filesystems/nfs/nfsd-maintainer-entry-profile.rst:188: ERROR: Unknown target name: "nfsdn". [docutils]
Documentation/filesystems/nfs/nfsd-maintainer-entry-profile.rst:192: ERROR: Unknown target name: "nfsd4m". [docutils]

These are due to Sphinx confusing function name prefixes for external
link syntax. Fix the warnings by inlining the prefixes.

Fixes: 3a1ce35030e1e0 ("NFSD: Add a subsystem policy document")
Reported-by: Stephen Rothwell 
Closes: https://lore.kernel.org/linux-next/20251117174218.29365f30@canb.auug.org.au/
Signed-off-by: Bagas Sanjaya 
Signed-off-by: Chuck Lever

NFSD: Add a subsystem policy document

2025-11-16T23:20:11+00:00

Steer contributors to NFSD's patchworks instance, list our patch
submission preferences, and more. The new document is based on the
existing netdev and xfs subsystem policy documents.

This is an attempt to add transparency to the process of accepting
contributions to NFSD and getting them merged upstream.

Suggested-by: "Darrick J. Wong" 
Cc: Luis Chamberlain 
Cc: Martin K. Petersen 
Reviewed-by: NeilBrown 
[ cel: Hand-edits to address review comments ]
Signed-off-by: Chuck Lever

nfsd: disallow file locking and delegations for NFSv4 reexport

2025-03-10T13:11:08+00:00

We do not and cannot support file locking with NFS reexport over
NFSv4.x for the same reason we don't do it for NFSv3: NFS reexport
server reboot cannot allow clients to recover locks because the source
NFS server has not rebooted, and so it is not in grace.  Since the
source NFS server is not in grace, it cannot offer any guarantees that
the file won't have been changed between the locks getting lost and
any attempt to recover/reclaim them.  The same applies to delegations
and any associated locks, so disallow them too.

Clients are no longer allowed to get file locks or delegations from a
reexport server, any attempts will fail with operation not supported.

Update the "Reboot recovery" section accordingly in
Documentation/filesystems/nfs/reexport.rst

Signed-off-by: Mike Snitzer 
Reviewed-by: Jeff Layton 
Signed-off-by: Chuck Lever

nfs: probe for LOCALIO when v3 client reconnects to server

2025-01-14T22:05:10+00:00

Re-enabling NFSv3 LOCALIO is made more complex (than NFSv4) because v3
is stateless.  As such, the hueristic used to identify a LOCALIO probe
point is more adhoc by nature: if/when NFSv3 client IO begins to
complete again in terms of normal RPC-based NFSv3 server IO, attempt
nfs_local_probe_async().

Care is taken to throttle the frequency of nfs_local_probe_async(),
otherwise there could be a flood of repeat calls to
nfs_local_probe_async().

The throttle is admin controlled using a new module parameter for
nfsv3, e.g.:
  echo 512 > /sys/module/nfsv3/parameters/nfs3_localio_probe_throttle

Probe for NFSv3 LOCALIO every N IO requests (512 in this case). Must
be power-of-2, defaults to 0 (probing disabled).

On systems that expect to use LOCALIO with NFSv3 the admin should
configure the 'nfs3_localio_probe_throttle' module parameter.

This commit backfills module parameter documentation in localio.rst

Signed-off-by: Mike Snitzer 
Reviewed-by: Jeff Layton 
Signed-off-by: Anna Schumaker