[PATCH 5/6] fuse: Remove fuse_direct_write_iter code path / use IOCB_DIRECT

[Bernd Schubert <bschubert@ddn.com>]

fuse_direct_write_iter is basically duplicating what is already
in fuse_cache_write_iter/generic_file_direct_write. That can be
avoided by setting IOCB_DIRECT in fuse_file_write_iter, after that
fuse_cache_write_iter can be used for the FOPEN_DIRECT_IO code path
and fuse_direct_write_iter can be removed.

Before it was using for FOPEN_DIRECT_IO

1) async (!is_sync_kiocb(iocb)) && IOCB_DIRECT

fuse_file_write_iter
    fuse_direct_write_iter
        fuse_direct_IO
            fuse_send_dio

2) sync (is_sync_kiocb(iocb)) or IOCB_DIRECT not being set

fuse_file_write_iter
    fuse_direct_write_iter
        fuse_send_dio

3) FOPEN_DIRECT_IO not set

Same as the consolidates path below

The new consolidated code path is always

fuse_file_write_iter
    fuse_cache_write_iter
        generic_file_write_iter
             __generic_file_write_iter
                 generic_file_direct_write
                     mapping->a_ops->direct_IO / fuse_direct_IO
                         fuse_send_dio

So in general for FOPEN_DIRECT_IO the code path gets longer. Additionally
fuse_direct_IO does an allocation of struct fuse_io_priv - might be a bit
slower in micro benchmarks.
Also, the IOCB_DIRECT information gets lost (as we now set it outselves).
But then IOCB_DIRECT is directly related to O_DIRECT set in
struct file::f_flags.

An additional change is for condition 2 above, which might will now do
async IO on the condition ff->fm->fc->async_dio. Given that async IO for
FOPEN_DIRECT_IO was especially introduced in commit
'commit 23c94e1cdcbf ("fuse: Switch to using async direct IO for
 FOPEN_DIRECT_IO")'
it should not matter. Especially as fuse_direct_IO is blocking for
is_sync_kiocb(), at worst it has another slight overhead.

Advantage is the removal of code paths and conditions and it is now also
possible to remove FOPEN_DIRECT_IO conditions in fuse_send_dio
(in a later patch).

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 | 54 ++++----------------------------------------------
 1 file changed, 4 insertions(+), 50 deletions(-)

diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index f9d21804d313..0b3363eec435 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1602,52 +1602,6 @@ static ssize_t fuse_direct_read_iter(struct kiocb *iocb, struct iov_iter *to)
 	return res;
 }
 
-static ssize_t fuse_direct_write_iter(struct kiocb *iocb, struct iov_iter *from)
-{
-	struct inode *inode = file_inode(iocb->ki_filp);
-	struct fuse_io_priv io = FUSE_IO_PRIV_SYNC(iocb);
-	ssize_t res;
-	bool exclusive_lock = fuse_dio_wr_exclusive_lock(iocb, from);
-
-	/*
-	 * Take exclusive lock if
-	 * - Parallel direct writes are disabled - a user space decision
-	 * - Parallel direct writes are enabled and i_size is being extended.
-	 *   This might not be needed at all, but needs further investigation.
-	 */
-	if (exclusive_lock)
-		inode_lock(inode);
-	else {
-		inode_lock_shared(inode);
-
-		/* A race with truncate might have come up as the decision for
-		 * the lock type was done without holding the lock, check again.
-		 */
-		if (fuse_io_past_eof(iocb, from)) {
-			inode_unlock_shared(inode);
-			inode_lock(inode);
-			exclusive_lock = true;
-		}
-	}
-
-	res = generic_write_checks(iocb, from);
-	if (res > 0) {
-		if (!is_sync_kiocb(iocb) && iocb->ki_flags & IOCB_DIRECT) {
-			res = fuse_direct_IO(iocb, from);
-		} else {
-			res = fuse_send_dio(&io, from, &iocb->ki_pos,
-					    FUSE_DIO_WRITE);
-			fuse_write_update_attr(inode, iocb->ki_pos, res);
-		}
-	}
-	if (exclusive_lock)
-		inode_unlock(inode);
-	else
-		inode_unlock_shared(inode);
-
-	return res;
-}
-
 static ssize_t fuse_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
 {
 	struct file *file = iocb->ki_filp;
@@ -1678,10 +1632,10 @@ static ssize_t fuse_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	if (FUSE_IS_DAX(inode))
 		return fuse_dax_write_iter(iocb, from);
 
-	if (!(ff->open_flags & FOPEN_DIRECT_IO))
-		return fuse_cache_write_iter(iocb, from);
-	else
-		return fuse_direct_write_iter(iocb, from);
+	if (ff->open_flags & FOPEN_DIRECT_IO)
+		iocb->ki_flags |= IOCB_DIRECT;
+
+	return fuse_cache_write_iter(iocb, from);
 }
 
 static void fuse_writepage_free(struct fuse_writepage_args *wpa)
-- 
2.39.2