[PATCH v2 0/3] fs/nfsd: accept a backdated timestamp from a delegation holder

[Jeff Layton <jlayton@kernel.org>]

The main problem is that an attribute delegation has strict rules about
updates can be done, and that prevents applications that backdate
timestamps on files after writing them, (e.g. tar -x, cp -p, etc.) from
setting them properly.

We could fix this on the client by making it always issue an RPC for the
SETATTR, but that would harm performance in these common use-cases.
This set allows the server to accept some of these backdated mtime
updates, by changing how the ctime is handled.

It'd be nice to see this in v7.4.

Signed-off-by: Jeff Layton <jlayton@kernel.org>
---
Changes in v2:
- Split the change into three patches
- Stamp now in inode_set_ctime_deleg() for a stale update, so nfsd need
  not compare
- Drop a SETATTR report that matches the inode, so an untouched file
  keeps its change attribute
- Set dl_setattr only on the branch that carries a c/mtime update
- Compare against the inode, not the grant-time snapshots (Chuck)
- Set the ctime whenever a CB_GETATTR moves the mtime
- Take i_rwsem before the CB_GETATTR comparison
- Drop the unused dl_atime, dl_mtime and dl_ctime, and make
  nfsd4_vet_deleg_time() static
- Link to v1: https://lore.kernel.org/r/20260901-delegts-v1-1-9937f7ee4370@kernel.org

---
Jeff Layton (3):
      fs: stamp the current time for a stale delegated ctime update
      nfsd: accept a backdated timestamp from a delegation holder
      nfsd: compare CB_GETATTR times against the inode

 fs/inode.c          | 17 +++++++++++----
 fs/nfsd/nfs4proc.c  | 63 +++++++++++++++++++++++++++++++++++++++++++----------
 fs/nfsd/nfs4state.c | 49 ++++++++++++++++++++++++++---------------
 fs/nfsd/state.h     |  8 -------
 4 files changed, 95 insertions(+), 42 deletions(-)
---
base-commit: ac579868af0c900d8fd9c8cfe9e10db46ccc5a75
change-id: 20260901-delegts-e91a648f1427

Best regards,
-- 
Jeff Layton <jlayton@kernel.org>