Re: [PATCH] NFS: Fix mode bits and nlink count for v4 referral dirs

[Trond Myklebust]

On Thu, 2020-10-15 at 00:39 +0530, Ashish Sangwan wrote:
> On Wed, Oct 14, 2020 at 11:47 PM Trond Myklebust
> <trondmy@xxxxxxxxxxxxxxx> wrote:
> > On Tue, 2020-10-06 at 08:14 -0700, Ashish Sangwan wrote:
> > > Request for mode bits and nlink count in the nfs4_get_referral
> > > call
> > > and if server returns them use them instead of hard coded values.
> > > 
> > > CC: stable@xxxxxxxxxxxxxxx
> > > Signed-off-by: Ashish Sangwan <ashishsangwan2@xxxxxxxxx>
> > > ---
> > >  fs/nfs/nfs4proc.c | 20 +++++++++++++++++---
> > >  1 file changed, 17 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/fs/nfs/nfs4proc.c b/fs/nfs/nfs4proc.c
> > > index 6e95c85fe395..efec05c5f535 100644
> > > --- a/fs/nfs/nfs4proc.c
> > > +++ b/fs/nfs/nfs4proc.c
> > > @@ -266,7 +266,9 @@ const u32 nfs4_fs_locations_bitmap[3] = {
> > >       | FATTR4_WORD0_FSID
> > >       | FATTR4_WORD0_FILEID
> > >       | FATTR4_WORD0_FS_LOCATIONS,
> > > -     FATTR4_WORD1_OWNER
> > > +     FATTR4_WORD1_MODE
> > > +     | FATTR4_WORD1_NUMLINKS
> > > +     | FATTR4_WORD1_OWNER
> > >       | FATTR4_WORD1_OWNER_GROUP
> > >       | FATTR4_WORD1_RAWDEV
> > >       | FATTR4_WORD1_SPACE_USED
> > > @@ -7594,16 +7596,28 @@ nfs4_listxattr_nfs4_user(struct inode
> > > *inode,
> > > char *list, size_t list_len)
> > >   */
> > >  static void nfs_fixup_referral_attributes(struct nfs_fattr
> > > *fattr)
> > >  {
> > > +     bool fix_mode = true, fix_nlink = true;
> > > +
> > >       if (!(((fattr->valid & NFS_ATTR_FATTR_MOUNTED_ON_FILEID) ||
> > >              (fattr->valid & NFS_ATTR_FATTR_FILEID)) &&
> > >             (fattr->valid & NFS_ATTR_FATTR_FSID) &&
> > >             (fattr->valid & NFS_ATTR_FATTR_V4_LOCATIONS)))
> > >               return;
> > > 
> > > +     if (fattr->valid & NFS_ATTR_FATTR_MODE)
> > > +             fix_mode = false;
> > > +     if (fattr->valid & NFS_ATTR_FATTR_NLINK)
> > > +             fix_nlink = false;
> > >       fattr->valid |= NFS_ATTR_FATTR_TYPE | NFS_ATTR_FATTR_MODE |
> > >               NFS_ATTR_FATTR_NLINK | NFS_ATTR_FATTR_V4_REFERRAL;
> > > -     fattr->mode = S_IFDIR | S_IRUGO | S_IXUGO;
> > > -     fattr->nlink = 2;
> > > +
> > > +     if (fix_mode)
> > > +             fattr->mode = S_IFDIR | S_IRUGO | S_IXUGO;
> > > +     else
> > > +             fattr->mode |= S_IFDIR;
> > > +
> > > +     if (fix_nlink)
> > > +             fattr->nlink = 2;
> > >  }
> > > 
> > >  static int _nfs4_proc_fs_locations(struct rpc_clnt *client,
> > > struct
> > > inode *dir,
> > 
> > NACK to this patch. The whole point is that if the server has a
> > referral, then it is not going to give us any attributes other than
> > the
> > ones we're already asking for because it may not even have a real
> > directory. The client is required to fake up an inode, hence the
> > existing code.
> 
> Hi Trond, thanks for reviewing the patch!
> Sorry but I didn't understand the reason to NACK it. Could you please
> elaborate your concern?
> These are the current attributes we request from the server on a
> referral:
> FATTR4_WORD0_CHANGE
> > FATTR4_WORD0_SIZE
> > FATTR4_WORD0_FSID
> > FATTR4_WORD0_FILEID
> > FATTR4_WORD0_FS_LOCATIONS,
> FATTR4_WORD1_OWNER
> > FATTR4_WORD1_OWNER_GROUP
> > FATTR4_WORD1_RAWDEV
> > FATTR4_WORD1_SPACE_USED
> > FATTR4_WORD1_TIME_ACCESS
> > FATTR4_WORD1_TIME_METADATA
> > FATTR4_WORD1_TIME_MODIFY
> > FATTR4_WORD1_MOUNTED_ON_FILEID,
> 
> So you are suggesting that it's ok to ask for SIZE, OWNER, OWNER
> GROUP, SPACE USED, TIMESTAMPs etc but not ok to ask for mode bits and
> numlinks?

No. We shouldn't be asking for any of that information for a referral
because the server isn't supposed to return any values for it.

Chuck and Anna, what's the deal with commit c05cefcc7241? That appears
to have changed the original code to speculatively assume that the
server will violate RFC5661 Section 11.3.1 and/or RFC7530 Section
8.3.1. Specifically, the paragraph that says:

"
   Other attributes SHOULD NOT be made available for absent file
   systems, even when it is possible to provide them.  The server should
   not assume that more information is always better and should avoid
   gratuitously providing additional information."

So why is the client asking for them?

-- 
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx