[PATCH v7 06/14] NFSD: Always set IOCB_SYNC in direct write path

[Chuck Lever <cel@kernel.org>]

From: Chuck Lever <chuck.lever@oracle.com>

The NFS specs mandate that an NFS_FILE_SYNC write means that file
metadata (eg time stamps) are durable before the server sends the
response.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 fs/nfsd/vfs.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
index cd2c99e450fb..74fcb12bf19c 100644
--- a/fs/nfsd/vfs.c
+++ b/fs/nfsd/vfs.c
@@ -1397,12 +1397,6 @@ nfsd_issue_write_dio(struct svc_rqst *rqstp, struct svc_fh *fhp,
 
 	trace_nfsd_write_direct(rqstp, fhp, in_offset, in_count);
 
-	/*
-	 * Any buffered IO issued here will be misaligned, use
-	 * sync IO to ensure it has completed before returning.
-	 */
-	kiocb->ki_flags |= IOCB_DSYNC;
-
 	*cnt = 0;
 	for (int i = 0; i < n_iters; i++) {
 		if (iter_is_dio_aligned[i])
@@ -1454,6 +1448,17 @@ nfsd_direct_write(struct svc_rqst *rqstp, struct svc_fh *fhp,
 	if (nf->nf_file->f_op->fop_flags & FOP_DONTCACHE)
 		kiocb->ki_flags |= IOCB_DONTCACHE;
 
+	/*
+	 * IOCB_SYNC + IOCB_DIRECT requests that iter_write should persist
+	 * both written data and dirty time stamps.
+	 *
+	 * When falling back to buffered I/O or handling the unaligned
+	 * first and last segments, the data and time stamps must be
+	 * durable before nfsd_vfs_write() returns to its caller, matching
+	 * the behavior of direct I/O.
+	 */
+	kiocb->ki_flags |= IOCB_SYNC | IOCB_DSYNC;
+
 	if (nfsd_is_write_dio_possible(kiocb->ki_pos, *cnt, nf, &write_dio))
 		return nfsd_issue_write_dio(rqstp, fhp, nf, nvecs, cnt, kiocb,
 					    &write_dio);
-- 
2.51.0