[RFC PATCH v3 01/18] block: Add check for async buffered writes to generic_write_checks

[Stefan Roesch <shr@fb.com>]

This introduces the flag FMODE_BUF_WASYNC. If devices support async
buffered writes, this flag can be set. It also modifies the check in
generic_write_checks to take async buffered writes into consideration.

Signed-off-by: Stefan Roesch <shr@fb.com>
---
 fs/read_write.c    | 4 +++-
 include/linux/fs.h | 3 +++
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/fs/read_write.c b/fs/read_write.c
index e643aec2b0ef..544d4df33f4f 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -1633,7 +1633,9 @@ int generic_write_checks_count(struct kiocb *iocb, loff_t *count)
 	if (iocb->ki_flags & IOCB_APPEND)
 		iocb->ki_pos = i_size_read(inode);
 
-	if ((iocb->ki_flags & IOCB_NOWAIT) && !(iocb->ki_flags & IOCB_DIRECT))
+	if ((iocb->ki_flags & IOCB_NOWAIT) &&
+		!((iocb->ki_flags & IOCB_DIRECT) ||
+		  (file->f_mode & FMODE_BUF_WASYNC)))
 		return -EINVAL;
 
 	return generic_write_check_limits(iocb->ki_filp, iocb->ki_pos, count);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index bbde95387a23..3b479d02e210 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -177,6 +177,9 @@ typedef int (dio_iodone_t)(struct kiocb *iocb, loff_t offset,
 /* File supports async buffered reads */
 #define FMODE_BUF_RASYNC	((__force fmode_t)0x40000000)
 
+/* File supports async nowait buffered writes */
+#define FMODE_BUF_WASYNC	((__force fmode_t)0x80000000)
+
 /*
  * Attribute flags.  These should be or-ed together to figure out what
  * has been changed!
-- 
2.30.2