Re: [PATCH v6 4/5] NFSD: allow client to use write delegation stateid for READ

[Jeff Layton <jlayton@kernel.org>]

On Thu, 2023-06-29 at 11:02 -0400, Chuck Lever wrote:
> On Wed, Jun 28, 2023 at 07:36:15PM -0700, Dai Ngo wrote:
> > Allow NFSv4 client to use write delegation stateid for READ operation.
> > Per RFC 8881 section 9.1.2. Use of the Stateid and Locking.
> 
> I'm wondering if this fix should precede 2/5 to prevent breakage
> during a bisect. Jeff, what do you think?
> 

Good point. Probably the patch that actually makes it actually hand out
write delegations should be the last one.
 
> 
> > Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
> > ---
> >  fs/nfsd/nfs4proc.c | 16 ++++++++++++++--
> >  fs/nfsd/nfs4xdr.c  |  9 +++++++++
> >  fs/nfsd/xdr4.h     |  2 ++
> >  3 files changed, 25 insertions(+), 2 deletions(-)
> > 
> > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > index 5ae670807449..3fa66cb38780 100644
> > --- a/fs/nfsd/nfs4proc.c
> > +++ b/fs/nfsd/nfs4proc.c
> > @@ -942,8 +942,18 @@ nfsd4_read(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
> >  	/* check stateid */
> >  	status = nfs4_preprocess_stateid_op(rqstp, cstate, &cstate->current_fh,
> >  					&read->rd_stateid, RD_STATE,
> > -					&read->rd_nf, NULL);
> > -
> > +					&read->rd_nf, &read->rd_wd_stid);
> > +	/*
> > +	 * rd_wd_stid is needed for nfsd4_encode_read to allow write
> > +	 * delegation stateid used for read. Its refcount is decremented
> > +	 * by nfsd4_read_release when read is done.
> > +	 */
> > +	if (!status && (read->rd_wd_stid->sc_type != NFS4_DELEG_STID ||
> > +			delegstateid(read->rd_wd_stid)->dl_type !=
> > +			NFS4_OPEN_DELEGATE_WRITE)) {
> > +		nfs4_put_stid(read->rd_wd_stid);
> > +		read->rd_wd_stid = NULL;
> > +	}
> >  	read->rd_rqstp = rqstp;
> >  	read->rd_fhp = &cstate->current_fh;
> >  	return status;
> > @@ -953,6 +963,8 @@ nfsd4_read(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
> >  static void
> >  nfsd4_read_release(union nfsd4_op_u *u)
> >  {
> > +	if (u->read.rd_wd_stid)
> > +		nfs4_put_stid(u->read.rd_wd_stid);
> >  	if (u->read.rd_nf)
> >  		nfsd_file_put(u->read.rd_nf);
> >  	trace_nfsd_read_done(u->read.rd_rqstp, u->read.rd_fhp,
> > diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> > index b35855c8beb6..833634cdc761 100644
> > --- a/fs/nfsd/nfs4xdr.c
> > +++ b/fs/nfsd/nfs4xdr.c
> > @@ -4125,6 +4125,7 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
> >  	struct file *file;
> >  	int starting_len = xdr->buf->len;
> >  	__be32 *p;
> > +	fmode_t o_fmode = 0;
> >  
> >  	if (nfserr)
> >  		return nfserr;
> > @@ -4144,10 +4145,18 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
> >  	maxcount = min_t(unsigned long, read->rd_length,
> >  			 (xdr->buf->buflen - xdr->buf->len));
> >  
> > +	if (read->rd_wd_stid) {
> > +		/* allow READ using write delegation stateid */
> > +		o_fmode = file->f_mode;
> > +		file->f_mode |= FMODE_READ;
> > +	}
> >  	if (file->f_op->splice_read && splice_ok)
> >  		nfserr = nfsd4_encode_splice_read(resp, read, file, maxcount);
> >  	else
> >  		nfserr = nfsd4_encode_readv(resp, read, file, maxcount);
> > +	if (o_fmode)
> > +		file->f_mode = o_fmode;
> > +
> >  	if (nfserr) {
> >  		xdr_truncate_encode(xdr, starting_len);
> >  		return nfserr;
> > diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
> > index 510978e602da..3ccc40f9274a 100644
> > --- a/fs/nfsd/xdr4.h
> > +++ b/fs/nfsd/xdr4.h
> > @@ -307,6 +307,8 @@ struct nfsd4_read {
> >  	struct svc_rqst		*rd_rqstp;          /* response */
> >  	struct svc_fh		*rd_fhp;            /* response */
> >  	u32			rd_eof;             /* response */
> > +
> > +	struct nfs4_stid	*rd_wd_stid;		/* internal */
> >  };
> >  
> >  struct nfsd4_readdir {
> > -- 
> > 2.39.3
> > 

-- 
Jeff Layton <jlayton@kernel.org>