[PATCH v2 07/13] fs: add support for async buffered writes

[Stefan Roesch <shr@fb.com>]

This adds support for the AOP_FLAGS_BUF_WASYNC flag to the fs layer. If
a page that is required for writing is not in the page cache, it returns
EAGAIN instead of ENOMEM.

Signed-off-by: Stefan Roesch <shr@fb.com>
---
 fs/buffer.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/fs/buffer.c b/fs/buffer.c
index ae588ae4b1c1..58331ef214b9 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -2062,6 +2062,7 @@ int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
 			*wait_bh++=bh;
 		}
 	}
+
 	/*
 	 * If we issued read requests - let them complete.
 	 */
@@ -2141,8 +2142,11 @@ int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
 		gfp = GFP_ATOMIC | __GFP_NOWARN;
 
 	page = grab_cache_page_write_begin(mapping, index, flags);
-	if (!page)
+	if (!page) {
+		if (no_wait)
+			return -EAGAIN;
 		return -ENOMEM;
+	}
 
 	status = __block_write_begin_int(page_folio(page), pos, len, get_block, NULL, gfp);
 	if (unlikely(status)) {
-- 
2.30.2