On Thu, 2025-02-13 at 11:37 -0800, Dai Ngo wrote:
> Allow read using write delegation stateid granted on OPENs with
> OPEN4_SHARE_ACCESS_WRITE only, to accommodate clients whose WRITE
> implementation may unavoidably do (e.g., due to buffer cache
> constraints).
>
> When this condition is detected in nfsd4_encode_read the access
> mode FMODE_READ is temporarily added to the file's f_mode and is
> removed when the read is done.
>
> Signed-off-by: Dai Ngo <dai.ngo@xxxxxxxxxx>
> ---
> fs/nfsd/nfs4proc.c | 15 ++++++++++++++-
> fs/nfsd/nfs4xdr.c | 8 ++++++++
> fs/nfsd/xdr4.h | 1 +
> 3 files changed, 23 insertions(+), 1 deletion(-)
>
> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
> index f6e06c779d09..be43627bbf78 100644
> --- a/fs/nfsd/nfs4proc.c
> +++ b/fs/nfsd/nfs4proc.c
> @@ -973,7 +973,18 @@ 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 &&
> + (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;
> @@ -984,6 +995,8 @@ 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 e67420729ecd..3996678bab3f 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -4498,6 +4498,7 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
> unsigned long maxcount;
> __be32 wire_data[2];
> struct file *file;
> + bool wronly = false;
>
> if (nfserr)
> return nfserr;
> @@ -4515,10 +4516,17 @@ nfsd4_encode_read(struct nfsd4_compoundres *resp, __be32 nfserr,
> maxcount = min_t(unsigned long, read->rd_length,
> (xdr->buf->buflen - xdr->buf->len));
>
> + if (!(file->f_mode & FMODE_READ) && read->rd_wd_stid) {
> + /* allow READ using write delegation stateid */
> + wronly = true;
> + file->f_mode |= FMODE_READ;
> + }
Is that really OK? Can we just upgrade the f_mode like that?
Also, what happens with more exotic exported filesystems like NFS?
For example, if I'm reexporting NFS, the backend NFS server may not
allow you to do a READ operation using a OPEN4_SHARE_ACCESS_WRITE only
stateid. Won't this break in that case?
> 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 (wronly)
> + file->f_mode &= ~FMODE_READ;
> if (nfserr) {
> xdr_truncate_encode(xdr, eof_offset);
> return nfserr;
> diff --git a/fs/nfsd/xdr4.h b/fs/nfsd/xdr4.h
> index c26ba86dbdfd..2f053beed899 100644
> --- a/fs/nfsd/xdr4.h
> +++ b/fs/nfsd/xdr4.h
> @@ -426,6 +426,7 @@ 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 {
--
Jeff Layton <jlayton@xxxxxxxxxx>
