[PATCH 2/2] nfs: expose FMODE_NOWAIT for O_DIRECT read files

[Dylan Yudaken <dyudaken@gmail.com>]

O_DIRECT reads already (mostly) handle async requests, with the
exception of locking the inode for direct.
Handle async requests properly by using nfs_start_io_direct_nowait,
and then expose FMODE_NOWAIT since it's now properly supported.

Signed-off-by: Dylan Yudaken <dyudaken@gmail.com>
---
 fs/nfs/direct.c |  5 ++++-
 fs/nfs/file.c   | 13 ++++++++++++-
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/nfs/direct.c b/fs/nfs/direct.c
index 48d89716193a..bf0bad971d22 100644
--- a/fs/nfs/direct.c
+++ b/fs/nfs/direct.c
@@ -473,7 +473,10 @@ ssize_t nfs_file_direct_read(struct kiocb *iocb, struct iov_iter *iter,
 		dreq->flags = NFS_ODIRECT_SHOULD_DIRTY;
 
 	if (!swap) {
-		result = nfs_start_io_direct(inode);
+		if (iocb->ki_flags & IOCB_NOWAIT)
+			result = nfs_start_io_direct_nowait(inode);
+		else
+			result = nfs_start_io_direct(inode);
 		if (result) {
 			/* release the reference that would usually be
 			 * consumed by nfs_direct_read_schedule_iovec()
diff --git a/fs/nfs/file.c b/fs/nfs/file.c
index 25048a3c2364..c5eb22036e71 100644
--- a/fs/nfs/file.c
+++ b/fs/nfs/file.c
@@ -72,8 +72,13 @@ nfs_file_open(struct inode *inode, struct file *filp)
 		return res;
 
 	res = nfs_open(inode, filp);
-	if (res == 0)
+	if (res == 0) {
 		filp->f_mode |= FMODE_CAN_ODIRECT;
+		/* flag NOWAIT on read-only O_DIRECT files only */
+		if ((filp->f_flags & O_DIRECT) &&
+		    !(filp->f_mode & FMODE_WRITE))
+			filp->f_mode |= FMODE_NOWAIT;
+	}
 	return res;
 }
 
@@ -705,6 +710,12 @@ ssize_t nfs_file_write(struct kiocb *iocb, struct iov_iter *from)
 
 	trace_nfs_file_write(iocb, from);
 
+	/*
+	 * FMODE_NOWAIT is not set for writable files
+	 */
+	if (WARN_ON_ONCE(iocb->ki_flags & IOCB_NOWAIT))
+		return -EAGAIN;
+
 	result = nfs_key_timeout_notify(file, inode);
 	if (result)
 		return result;
-- 
2.50.1