[PATCH 2/3] NFSD: add new NFSD_IO_DIRECT variants that may override stable_how

Mike Snitzer
2025-11-04T16:42:33Z

NFSD_IO_DIRECT_WRITE_FILE_SYNC is direct IO with stable_how=NFS_FILE_SYNC.
NFSD_IO_DIRECT_WRITE_DATA_SYNC is direct IO with stable_how=NFS_DATA_SYNC.

The stable_how associated with each is a hint in the form of a "floor"
value for stable_how. Meaning if the client provided stable_how is
already of higher value it will not be changed.

These permutations of NFSD_IO_DIRECT allow to experiment with also
elevating stable_how and sending it back to the client. Which for
NFSD_IO_DIRECT_WRITE_FILE_SYNC will cause the client to elide its
COMMIT.

Signed-off-by: Mike Snitzer <snitzer@kernel.org>
---
fs/nfsd/debugfs.c | 7 ++++++-
fs/nfsd/nfsd.h | 2 ++
fs/nfsd/vfs.c | 46 ++++++++++++++++++++++++++++++++++------------
3 files changed, 42 insertions(+), 13 deletions(-)

diff --git a/fs/nfsd/debugfs.c b/fs/nfsd/debugfs.c
index 7f44689e0a53..8538e29ed2ab 100644
--- a/fs/nfsd/debugfs.c
+++ b/fs/nfsd/debugfs.c
@@ -68,7 +68,7 @@ static int nfsd_io_cache_read_set(void *data, u64 val)
case NFSD_IO_DIRECT:
/*
* Must disable splice_read when enabling
- * NFSD_IO_DONTCACHE.
+ * NFSD_IO_DONTCACHE and NFSD_IO_DIRECT.
*/
nfsd_disable_splice_read = true;
nfsd_io_cache_read = val;
@@ -90,6 +90,9 @@ DEFINE_DEBUGFS_ATTRIBUTE(nfsd_io_cache_read_fops, nfsd_io_cache_read_get,
* Contents:
* %0: NFS WRITE will use buffered IO
* %1: NFS WRITE will use dontcache (buffered IO w/ dropbehind)
+ * %2: NFS WRITE will use direct IO with stable_how=NFS_UNSTABLE
+ * %3: NFS WRITE will use direct IO with stable_how=NFS_DATA_SYNC
+ * %4: NFS WRITE will use direct IO with stable_how=NFS_FILE_SYNC
*
* This setting takes immediate effect for all NFS versions,
* all exports, and in all NFSD net namespaces.
@@ -109,6 +112,8 @@ static int nfsd_io_cache_write_set(void *data, u64 val)
case NFSD_IO_BUFFERED:
case NFSD_IO_DONTCACHE:
case NFSD_IO_DIRECT:
+ case NFSD_IO_DIRECT_WRITE_DATA_SYNC:
+ case NFSD_IO_DIRECT_WRITE_FILE_SYNC:
nfsd_io_cache_write = val;
break;
default:
diff --git a/fs/nfsd/nfsd.h b/fs/nfsd/nfsd.h
index e4263326ca4a..10eca169392b 100644
--- a/fs/nfsd/nfsd.h
+++ b/fs/nfsd/nfsd.h
@@ -161,6 +161,8 @@ enum {
NFSD_IO_BUFFERED,
NFSD_IO_DONTCACHE,
NFSD_IO_DIRECT,
+ NFSD_IO_DIRECT_WRITE_DATA_SYNC,
+ NFSD_IO_DIRECT_WRITE_FILE_SYNC,
};

extern u64 nfsd_io_cache_read __read_mostly;
diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index 9403ec8bb2da..99c62340f58f 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1407,15 +1407,45 @@ nfsd_issue_dio_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
return 0;
}

+static void
+nfsd_init_write_kiocb_from_stable(u32 stable_floor,
+ struct kiocb *kiocb,
+ u32 *stable_how)
+{
+ if (stable_floor < *stable_how)
+ return; /* stable_how already set higher */
+
+ *stable_how = stable_floor;
+
+ switch (stable_floor) {
+ case NFS_FILE_SYNC:
+ /* persist data and timestamps */
+ kiocb->ki_flags |= IOCB_DSYNC | IOCB_SYNC;
+ break;
+ case NFS_DATA_SYNC:
+ /* persist data only */
+ kiocb->ki_flags |= IOCB_DSYNC;
+ break;
+ }
+}
+
static noinline_for_stack int
nfsd_direct_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
struct nfsd_file *nf, u32 *stable_how, unsigned int nvecs,
unsigned long *cnt, struct kiocb *kiocb)
{
struct nfsd_write_dio_args args;
+ u32 stable_floor = NFS_UNSTABLE;

args.nf = nf;

+ if (nfsd_io_cache_write == NFSD_IO_DIRECT_WRITE_FILE_SYNC)
+ stable_floor = NFS_FILE_SYNC;
+ else if (nfsd_io_cache_write == NFSD_IO_DIRECT_WRITE_DATA_SYNC)
+ stable_floor = NFS_DATA_SYNC;
+ if (stable_floor != NFS_UNSTABLE)
+ nfsd_init_write_kiocb_from_stable(stable_floor, kiocb,
+ stable_how);
/*
* IOCB_DONTCACHE preserves the intent of NFSD_IO_DIRECT when
* falling back to buffered IO if entire WRITE is unaligned.
@@ -1490,18 +1520,8 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
stable = NFS_UNSTABLE;
init_sync_kiocb(&kiocb, file);
kiocb.ki_pos = offset;
- if (likely(!fhp->fh_use_wgather)) {
- switch (stable) {
- case NFS_FILE_SYNC:
- /* persist data and timestamps */
- kiocb.ki_flags |= IOCB_DSYNC | IOCB_SYNC;
- break;
- case NFS_DATA_SYNC:
- /* persist data only */
- kiocb.ki_flags |= IOCB_DSYNC;
- break;
- }
- }
+ if (likely(!fhp->fh_use_wgather))
+ nfsd_init_write_kiocb_from_stable(stable, &kiocb, stable_how);

nvecs = xdr_buf_to_bvec(rqstp->rq_bvec, rqstp->rq_maxpages, payload);

@@ -1511,6 +1531,8 @@ nfsd_vfs_write(struct svc_rqst *rqstp, struct svc_fh *fhp,

switch (nfsd_io_cache_write) {
case NFSD_IO_DIRECT:
+ case NFSD_IO_DIRECT_WRITE_DATA_SYNC:
+ case NFSD_IO_DIRECT_WRITE_FILE_SYNC:
host_err = nfsd_direct_write(rqstp, fhp, nf, stable_how,
nvecs, cnt, &kiocb);
stable = *stable_how;
--
2.44.0