[PATCH v4 1/2] fuse: preserve FOPEN_PARALLEL_DIRECT_WRITES for passthrough opens

[Russ Fellows]

fuse_file_io_open() clears FOPEN_PARALLEL_DIRECT_WRITES for any open
that lacks FOPEN_DIRECT_IO.  That rule is too strict for passthrough
opens, which already bypass the page cache through the backing file
and do not need FOPEN_DIRECT_IO to guarantee direct-I/O semantics.
Clearing the flag before the passthrough write path sees it prevents
the kernel from ever taking the shared-lock path for passthrough writes.

Introduce FOPEN_IOMODE_CACHED() to test for cached (page-cache) iomode
-- neither FOPEN_DIRECT_IO nor FOPEN_PASSTHROUGH set -- and use it to
guard the FOPEN_PARALLEL_DIRECT_WRITES stripping.  Passthrough and
direct-IO opens both bypass the page cache, so both are now eligible to
enable parallel direct writes.

While here, simplify fuse_file_io_open(): drop the early return for the
pure direct-IO case and dispatch the caching open through the same
FOPEN_IOMODE_CACHED() test, so a pure direct-IO open simply performs no
iomode setup instead of returning early.

This is a prerequisite for passthrough write parallelism; without it the
shared-lock path in the subsequent patch never activates.

Suggested-by: Amir Goldstein <amir73il@xxxxxxxxx>
Signed-off-by: Russ Fellows <russ.fellows@xxxxxxxxx>
---
 fs/fuse/iomode.c | 23 ++++++++++++-----------
 1 file changed, 12 insertions(+), 11 deletions(-)

diff --git a/fs/fuse/iomode.c b/fs/fuse/iomode.c
index 3728933..937d9e6 100644
--- a/fs/fuse/iomode.c
+++ b/fs/fuse/iomode.c
@@ -192,12 +192,18 @@ static int fuse_file_passthrough_open(struct inode *inode, struct file *file)
 	return err;
 }
 
+/* Fuse uses page cache if no passthrough nor direct_io open specified */
+#define FOPEN_IOMODE(oflags) \
+	((oflags) & (FOPEN_DIRECT_IO | FOPEN_PASSTHROUGH))
+#define FOPEN_IOMODE_CACHED(oflags) \
+	(FOPEN_IOMODE(oflags) == 0)
+
 /* Request access to submit new io to inode via open file */
 int fuse_file_io_open(struct file *file, struct inode *inode)
 {
 	struct fuse_file *ff = file->private_data;
 	struct fuse_inode *fi = get_fuse_inode(inode);
-	int err;
+	int err = 0;
 
 	/*
 	 * io modes are not relevant with DAX and with server that does not
@@ -216,25 +222,20 @@ int fuse_file_io_open(struct file *file, struct inode *inode)
 
 	/*
 	 * FOPEN_PARALLEL_DIRECT_WRITES requires FOPEN_DIRECT_IO.
+	 * Note that if user opens a file open with O_DIRECT, but server did
+	 * not specify FOPEN_DIRECT_IO, a later fcntl() could remove O_DIRECT,
+	 * so we put the inode in caching mode to prevent parallel dio.
 	 */
-	if (!(ff->open_flags & FOPEN_DIRECT_IO))
+	if (FOPEN_IOMODE_CACHED(ff->open_flags))
 		ff->open_flags &= ~FOPEN_PARALLEL_DIRECT_WRITES;
 
 	/*
 	 * First passthrough file open denies caching inode io mode.
 	 * First caching file open enters caching inode io mode.
-	 *
-	 * Note that if user opens a file open with O_DIRECT, but server did
-	 * not specify FOPEN_DIRECT_IO, a later fcntl() could remove O_DIRECT,
-	 * so we put the inode in caching mode to prevent parallel dio.
 	 */
-	if ((ff->open_flags & FOPEN_DIRECT_IO) &&
-	    !(ff->open_flags & FOPEN_PASSTHROUGH))
-		return 0;
-
 	if (ff->open_flags & FOPEN_PASSTHROUGH)
 		err = fuse_file_passthrough_open(inode, file);
-	else
+	else if (FOPEN_IOMODE_CACHED(ff->open_flags))
 		err = fuse_file_cached_io_open(inode, ff);
 	if (err)
 		goto fail;
-- 
2.51.0