[PATCH 5/5] NFSD: Honor OPEN4_SHARE_ACCESS_WANT_READ_DELEG on a read-write OPEN

[Chuck Lever <cel@kernel.org>]

RFC 8881 Section 18.16.3 defines OPEN4_SHARE_ACCESS_WANT_READ_DELEG
as a request for an OPEN_DELEGATE_READ delegation regardless of the
access bits in the OPEN. NFSD chooses the delegation type from the
access bits alone, so an OPEN for both read and write that sets
WANT_READ_DELEG gets a write delegation.

Any other client's open recalls that write delegation, and another
client's GETATTR triggers a CB_GETATTR. The read delegation the
client asked for survives both. Granting no delegation would also
respect the request, but it withholds a delegation NFSD is able to
grant.

Try for a read delegation when the OPEN sets WANT_READ_DELEG and
includes read access. After this change, a write-only OPEN that
sets WANT_READ_DELEG gets no delegation, with ond_why set to
WND4_RESOURCE. When the OPEN also sets
OPEN4_SHARE_ACCESS_WANT_OPEN_XOR_DELEGATION, return the open
stateid along with the read delegation.

Signed-off-by: Chuck Lever <cel@kernel.org>
---
 fs/nfsd/nfs4state.c | 20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index 6bb70d50e9d9..920967dd6f84 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -6984,6 +6984,12 @@ static bool nfsd4_want_deleg_timestamps(const struct nfsd4_open *open)
 	return open->op_deleg_want & OPEN4_SHARE_ACCESS_WANT_DELEG_TIMESTAMPS;
 }
 
+static bool nfsd4_want_read_deleg(const struct nfsd4_open *open)
+{
+	return (open->op_deleg_want & NFS4_SHARE_WANT_TYPE_MASK) ==
+		OPEN4_SHARE_ACCESS_WANT_READ_DELEG;
+}
+
 static void
 nfs4_delegation_record_grant_slot(struct nfs4_delegation *dp,
 				 const struct nfsd4_compound_state *cstate)
@@ -7041,14 +7047,16 @@ nfs4_set_delegation(struct nfsd4_open *open,
 	 *  We choose to offer a write delegation for OPEN with the
 	 *  OPEN4_SHARE_ACCESS_WRITE access mode to accommodate such clients.
 	 */
-	if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE) {
+	if ((open->op_share_access & NFS4_SHARE_ACCESS_WRITE) &&
+	    !nfsd4_want_read_deleg(open)) {
 		nf = find_writeable_file(fp);
 		dl_type = deleg_ts ? OPEN_DELEGATE_WRITE_ATTRS_DELEG : OPEN_DELEGATE_WRITE;
 	}
 
 	/*
-	 * If the file is being opened O_RDONLY or we couldn't get a O_RDWR
-	 * file for some reason, then try for a read delegation instead.
+	 * A read delegation can go to a client that holds a write open
+	 * of the file: nfsd_breaker_owns_lease() keeps the holder's own
+	 * opens from breaking it.
 	 */
 	if (!nf && (open->op_share_access & NFS4_SHARE_ACCESS_READ)) {
 		nf = find_readable_file(fp);
@@ -7325,7 +7333,7 @@ nfs4_open_delegation(struct svc_rqst *rqstp, struct nfsd4_open *open,
 
 	memcpy(&open->op_delegate_stateid, &dp->dl_stid.sc_stateid, sizeof(dp->dl_stid.sc_stateid));
 
-	if (open->op_share_access & NFS4_SHARE_ACCESS_WRITE) {
+	if (deleg_is_write(dp->dl_type)) {
 		struct file *f;
 
 		f = rcu_dereference_protected(dp->dl_stid.sc_file->fi_deleg_file, 1)->nf_file;
@@ -7371,6 +7379,10 @@ static bool open_xor_delegation(struct nfsd4_open *open)
 	/* Did we actually get a delegation? */
 	if (!deleg_is_read(open->op_delegate_type) && !deleg_is_write(open->op_delegate_type))
 		return false;
+	/* A read delegation stateid does not permit WRITE. */
+	if (deleg_is_read(open->op_delegate_type) &&
+	    (open->op_share_access & NFS4_SHARE_ACCESS_WRITE))
+		return false;
 	return true;
 }
 

-- 
2.55.0