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>

> 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>
> ---

There's a bunch of Sashiko comments outstanding, Jeff. Let me know, if I
can ignore them.

--

On Fri, 2026-09-04 at 12:50 +0200, Christian Brauner wrote:
> > 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>
> > ---
> 
> There's a bunch of Sashiko comments outstanding, Jeff. Let me know, if I
> can ignore them.


At least one of them looks valid. I'll plan to send a v3.

Thanks,
-- 
Jeff Layton <jlayton@kernel.org>

On Wed, Sep 2, 2026, at 2:54 PM, Jeff Layton wrote:
> 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>

Since the series modifies fs/inode.c, Christian will want to take it
through the VFS tree.

Acked-by: Chuck Lever <cel@kernel.org>


-- 
Chuck Lever (Come to NFS bake-a-thon! https://nfsv4bat.org)

On Wed, Sep 02, 2026 at 08:03:53PM -0400, Chuck Lever wrote:
> 
> 
> On Wed, Sep 2, 2026, at 2:54 PM, Jeff Layton wrote:
> > 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>
> 
> Since the series modifies fs/inode.c, Christian will want to take it
> through the VFS tree.
> 
> Acked-by: Chuck Lever <cel@kernel.org>

Thanks!