[PATCH v4 2/3] NFSD: add new NFSD_IO_DIRECT variants that may override stable_how

[Mike Snitzer <snitzer@kernel.org>]

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 a4700c917c72..1b61185e96a9 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1367,15 +1367,45 @@ nfsd_write_dio_iters_init(struct bio_vec *bvec, unsigned int nvecs,
 		args->flags_buffered |= IOCB_DONTCACHE;
 }
 
+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)
 {
+	u32 stable_floor = NFS_UNSTABLE;
 	struct nfsd_write_dio_args args;
 	ssize_t host_err;
 	unsigned int i;
 
+	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);
 	args.nf = nf;
 	nfsd_write_dio_iters_init(rqstp->rq_bvec, nvecs, kiocb, *cnt, &args);
 
@@ -1461,18 +1491,8 @@ 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);
 
@@ -1482,6 +1502,8 @@ 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