Re: [PATCH 1/1] NFSD fix handling of NFSv4.2 SEEK for data within the last hole

["J. Bruce Fields" <bfields@redhat.com>]

On Thu, Apr 01, 2021 at 09:27:56AM -0400, Olga Kornievskaia wrote:
> On Wed, Mar 31, 2021 at 9:50 PM J. Bruce Fields <bfields@redhat.com> wrote:
> >
> > On Wed, Mar 31, 2021 at 03:28:19PM -0400, Olga Kornievskaia wrote:
> > > From: Olga Kornievskaia <kolga@netapp.com>
> > >
> > > According to the RFC 7862, "if the server cannot find a
> > > corresponding sa_what, then the status will still be NFS4_OK,
> > > but sr_eof would be TRUE". If there is a file that ends with
> > > a hole and a SEEK request made for sa_what=SEEK_DATA with
> > > an offset in the middle of the last hole, then the server
> > > has to return OK and set the eof. Currently the linux server
> > > returns ERR_NXIO.
> >
> > Makes sense, but I think you can use the return value from vfs_llseek
> > instead of checking the file size again.  E.g.:
> >
> >         seek->seek_pos = vfs_llseek(nfs->nf_file, seek->seek_offset, whence);
> >         if (seek->seek_pos == -ENXIO)
> >                 seek->seek_eof = true;
> 
> I don't believe this is correct. (1) ENXIO doesn't imply eof. If the
> specified seek_offset was beyond the end of the file the server must
> return ERR_NXIO and not OK.

OK, never mind.

> and (2) for the same reason I need to
> check if the requested type was looking for data but didn't find it
> because the offset is in the middle of the hole but still within the
> file size (thus the need to check if the seek_offset is within the
> file size). But I'm happy to check specifically if the seek_pos was
> ENXIO (and not the generic negative error) and then also check if
> request was for data and request was within file size.
> 
> Also while I'm fixing this and have your attention, Can you tell if
> the "else if" condition in the original code makes sense to you. I
> didn't touch it but I don't think it's correct. "else if
> (seek->seek_pos >= i_size_read(file_inode(nf->nf_file)))" I don't
> believe this can ever happen. How can vfs_llseek() ever return a
> position that is greater than the size of the file (or actually even
> equal to it)?

I agree, I don't get it either.

--b.

> 
> >         else if (seek->seek_pos < 0)
> >                 status = nfserrno(seek->seek_pos);
> >
> > --b.
> >
> > >
> > > Fixes: 24bab491220fa ("NFSD: Implement SEEK")
> > > Signed-off-by: Olga Kornievskaia <kolga@netapp.com>
> > > ---
> > >  fs/nfsd/nfs4proc.c | 10 +++++++---
> > >  1 file changed, 7 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > > index e13c4c81fb89..2e7ceb9f1d5d 100644
> > > --- a/fs/nfsd/nfs4proc.c
> > > +++ b/fs/nfsd/nfs4proc.c
> > > @@ -1737,9 +1737,13 @@ nfsd4_seek(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
> > >        *        should ever file->f_pos.
> > >        */
> > >       seek->seek_pos = vfs_llseek(nf->nf_file, seek->seek_offset, whence);
> > > -     if (seek->seek_pos < 0)
> > > -             status = nfserrno(seek->seek_pos);
> > > -     else if (seek->seek_pos >= i_size_read(file_inode(nf->nf_file)))
> > > +     if (seek->seek_pos < 0) {
> > > +             if (whence == SEEK_DATA &&
> > > +                 seek->seek_offset < i_size_read(file_inode(nf->nf_file)))
> > > +                     seek->seek_eof = true;
> > > +             else
> > > +                     status = nfserrno(seek->seek_pos);
> > > +     } else if (seek->seek_pos >= i_size_read(file_inode(nf->nf_file)))
> > >               seek->seek_eof = true;
> > >
> > >  out:
> > > --
> > > 2.18.2
> > >
> >
>