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

[Chuck Lever <cel@kernel.org>]

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?


> 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
>