[PATCH 3/6] fuse: Allow parallel direct writes for O_DIRECT

[Bernd Schubert <bschubert@ddn.com>]

Take a shared lock in fuse_cache_write_iter. This was already
done for FOPEN_DIRECT_IO in

commit 153524053bbb ("fuse: allow non-extending parallel direct
writes on the same file")

but so far missing for plain O_DIRECT. Server side needs
to set FOPEN_PARALLEL_DIRECT_WRITES in order to signal that
it supports parallel dio writes.

Cc: Hao Xu <howeyxu@tencent.com>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Dharmendra Singh <dsingh@ddn.com>
Cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Bernd Schubert <bschubert@ddn.com>
---
 fs/fuse/file.c | 18 ++++++++++++++++--
 1 file changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index 6b8b9512c336..a6b99bc80fe7 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1314,6 +1314,10 @@ static bool fuse_dio_wr_exclusive_lock(struct kiocb *iocb, struct iov_iter *from
 	struct file *file = iocb->ki_filp;
 	struct fuse_file *ff = file->private_data;
 
+	/* this function is about direct IO only */
+	if (!(iocb->ki_flags & IOCB_DIRECT))
+		return false;
+
 	/* server side has to advise that it supports parallel dio writes */
 	if (!(ff->open_flags & FOPEN_PARALLEL_DIRECT_WRITES))
 		return false;
@@ -1337,6 +1341,7 @@ static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	struct inode *inode = mapping->host;
 	ssize_t err;
 	struct fuse_conn *fc = get_fuse_conn(inode);
+	bool excl_lock = fuse_dio_wr_exclusive_lock(iocb, from);
 
 	if (fc->writeback_cache && !(iocb->ki_flags & IOCB_DIRECT)) {
 		/* Update size (EOF optimization) and mode (SUID clearing) */
@@ -1355,7 +1360,10 @@ static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	}
 
 writethrough:
-	inode_lock(inode);
+	if (excl_lock)
+		inode_lock(inode);
+	else
+		inode_lock_shared(inode);
 
 	err = generic_write_checks(iocb, from);
 	if (err <= 0)
@@ -1370,6 +1378,9 @@ static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		goto out;
 
 	if (iocb->ki_flags & IOCB_DIRECT) {
+		/* file extending writes will trigger i_size_write - exclusive
+		 * lock is needed
+		 */
 		written = generic_file_direct_write(iocb, from);
 		if (written < 0 || !iov_iter_count(from))
 			goto out;
@@ -1379,7 +1390,10 @@ static ssize_t fuse_cache_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		written = fuse_perform_write(iocb, from);
 	}
 out:
-	inode_unlock(inode);
+	if (excl_lock)
+		inode_unlock(inode);
+	else
+		inode_unlock_shared(inode);
 	if (written > 0)
 		written = generic_write_sync(iocb, written);
 
-- 
2.39.2