Re: [PATCH rfc 2/2] NFSD: allow client to use write delegation stateid for READ

[Chuck Lever <chuck.lever@oracle.com>]

On Sat, Jul 27, 2024 at 03:53:41PM -0400, Chuck Lever wrote:
> On Sat, Jul 27, 2024 at 10:26:24PM +0300, Sagi Grimberg wrote:
> > 
> > 
> > 
> > On 26/07/2024 17:06, Chuck Lever wrote:
> > > On Wed, Jul 24, 2024 at 10:01:38AM -0700, Sagi Grimberg wrote:
> > > > Based on a patch fom Dai Ngo, allow NFSv4 client to use write delegation
> > > > stateid for READ operation. Per RFC 8881 section 9.1.2. Use of the
> > > > Stateid and Locking.
> > > > 
> > > > In addition, for anonymous stateids, check for pending delegations by
> > > > the filehandle and client_id, and if a conflict found, recall the delegation
> > > > before allowing the read to take place.
> > > > 
> > > > Suggested-by: Dai Ngo <dai.ngo@oracle.com>
> > > > Signed-off-by: Sagi Grimberg <sagi@grimberg.me>
> > > > ---
> > > >   fs/nfsd/nfs4proc.c  | 22 +++++++++++++++++++--
> > > >   fs/nfsd/nfs4state.c | 47 +++++++++++++++++++++++++++++++++++++++++++++
> > > >   fs/nfsd/nfs4xdr.c   |  9 +++++++++
> > > >   fs/nfsd/state.h     |  2 ++
> > > >   fs/nfsd/xdr4.h      |  2 ++
> > > >   5 files changed, 80 insertions(+), 2 deletions(-)
> > > > 
> > > > diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> > > > index 7b70309ad8fb..324984ec70c6 100644
> > > > --- a/fs/nfsd/nfs4proc.c
> > > > +++ b/fs/nfsd/nfs4proc.c
> > > > @@ -979,8 +979,24 @@ 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) {
> > > > +		if (!read->rd_wd_stid) {
> > > > +			/* special stateid? */
> > > > +			status = nfsd4_deleg_read_conflict(rqstp, cstate->clp,
> > > > +				&cstate->current_fh);
> > > > +		} else if (read->rd_wd_stid->sc_type != SC_TYPE_DELEG ||
> > > > +			   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;
> > > > @@ -990,6 +1006,8 @@ 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/nfs4state.c b/fs/nfsd/nfs4state.c
> > > > index dc61a8adfcd4..7e6b9fb31a4c 100644
> > > > --- a/fs/nfsd/nfs4state.c
> > > > +++ b/fs/nfsd/nfs4state.c
> > > > @@ -8805,6 +8805,53 @@ nfsd4_get_writestateid(struct nfsd4_compound_state *cstate,
> > > >   	get_stateid(cstate, &u->write.wr_stateid);
> > > >   }
> > > > +/**
> > > > + * nfsd4_deleg_read_conflict - Recall if read causes conflict
> > > > + * @rqstp: RPC transaction context
> > > > + * @clp: nfs client
> > > > + * @fhp: nfs file handle
> > > > + * @inode: file to be checked for a conflict
> > > > + * @modified: return true if file was modified
> > > > + * @size: new size of file if modified is true
> > > > + *
> > > > + * This function is called when there is a conflict between a write
> > > > + * delegation and a read that is using a special stateid where the
> > > > + * we cannot derive the client stateid exsistence. The server
> > > > + * must recall a conflicting delegation before allowing the read
> > > > + * to continue.
> > > > + *
> > > > + * Returns 0 if there is no conflict; otherwise an nfs_stat
> > > > + * code is returned.
> > > > + */
> > > > +__be32 nfsd4_deleg_read_conflict(struct svc_rqst *rqstp,
> > > > +		struct nfs4_client *clp, struct svc_fh *fhp)
> > > > +{
> > > > +	struct nfs4_file *fp;
> > > > +	__be32 status = 0;
> > > > +
> > > > +	fp = nfsd4_file_hash_lookup(fhp);
> > > > +	if (!fp)
> > > > +		return nfs_ok;
> > > > +
> > > > +	spin_lock(&state_lock);
> > > > +	spin_lock(&fp->fi_lock);
> > > > +	if (!list_empty(&fp->fi_delegations) &&
> > > > +	    !nfs4_delegation_exists(clp, fp)) {
> > > > +		/* conflict, recall deleg */
> > > > +		status = nfserrno(nfsd_open_break_lease(fp->fi_inode,
> > > > +					NFSD_MAY_READ));
> > > > +		if (status)
> > > > +			goto out;
> > > > +		if (!nfsd_wait_for_delegreturn(rqstp, fp->fi_inode))
> > > > +			status = nfserr_jukebox;
> > > > +	}
> > > > +out:
> > > > +	spin_unlock(&fp->fi_lock);
> > > > +	spin_unlock(&state_lock);
> > > > +	return status;
> > > > +}
> > > > +
> > > > +
> > > >   /**
> > > >    * nfsd4_deleg_getattr_conflict - Recall if GETATTR causes conflict
> > > >    * @rqstp: RPC transaction context
> > > > diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> > > > index c7bfd2180e3f..f0fe526fac3c 100644
> > > > --- a/fs/nfsd/nfs4xdr.c
> > > > +++ b/fs/nfsd/nfs4xdr.c
> > > > @@ -4418,6 +4418,7 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
> > > >   	unsigned long maxcount;
> > > >   	struct file *file;
> > > >   	__be32 *p;
> > > > +	fmode_t o_fmode = 0;
> > > >   	if (nfserr)
> > > >   		return nfserr;
> > > > @@ -4437,10 +4438,18 @@ 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;
> > > > +	}
> > > nfsd4_encode_read_plus() needs to handle write delegation stateids
> > > as well.
> > 
> > Yes, missed that one.
> > 
> > > 
> > > I'm not too sure about modifying the f_mode on an nfsd_file you
> > > just got from a cache of shared nfsd_files.
> > 
> > If that is a problem, nfsd can open the file with rw access to begin with
> > if a write deleg was given?
> 
> IMO, it's not a question of whether there is a write delegation, but
> rather what intent the client told the server during the OPEN. The
> server would need to open the local file for R/W when it gets a
> O_WRONLY open. Not saying this is the right thing to do, just
> thinking out loud...

OK, thinking about this again... The nfsd_file that is associated
with a write delegation is probably going to need to be a local
O_RDWR open, if a write delegation state ID can be used for READ or
WRITE.


-- 
Chuck Lever