[PATCH 5/7] nonblocking aio: ext4

[Goldwyn Rodrigues <rgoldwyn@suse.de>]

From: Goldwyn Rodrigues <rgoldwyn@suse.com>

Return EAGAIN if any of the following checks fail for direct I/O:
 + i_rwsem is lockable
 + Writing beyond end of file (will trigger allocation)
 + Blocks are allocated at the write location

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
 fs/ext4/file.c | 28 ++++++++++++++++++++++------
 1 file changed, 22 insertions(+), 6 deletions(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 2a822d3..c8d1e41 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -93,11 +93,16 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct inode *inode = file_inode(iocb->ki_filp);
 	int o_direct = iocb->ki_flags & IOCB_DIRECT;
+	int nonblocking = iocb->ki_flags & IOCB_NONBLOCKING;
 	int unaligned_aio = 0;
 	int overwrite = 0;
 	ssize_t ret;
 
-	inode_lock(inode);
+	if (o_direct && nonblocking) {
+		if (!inode_trylock(inode))
+			return -EAGAIN;
+	} else
+		inode_lock(inode);
 	ret = generic_write_checks(iocb, from);
 	if (ret <= 0)
 		goto out;
@@ -132,12 +137,18 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	if (o_direct) {
 		size_t length = iov_iter_count(from);
 		loff_t pos = iocb->ki_pos;
+		unsigned int blkbits = inode->i_blkbits;
+
+		if (nonblocking
+			&& (pos + length > EXT4_BLOCK_ALIGN(i_size_read(inode), blkbits))) {
+			ret = -EAGAIN;
+			goto out;
+		}
 
 		/* check whether we do a DIO overwrite or not */
-		if (ext4_should_dioread_nolock(inode) && !unaligned_aio &&
-		    pos + length <= i_size_read(inode)) {
+		if ((ext4_should_dioread_nolock(inode) && !unaligned_aio &&
+			    pos + length <= i_size_read(inode)) || nonblocking) {
 			struct ext4_map_blocks map;
-			unsigned int blkbits = inode->i_blkbits;
 			int err, len;
 
 			map.m_lblk = pos >> blkbits;
@@ -157,8 +168,13 @@ ext4_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 			 * non-flags are returned.  So we should check
 			 * these two conditions.
 			 */
-			if (err == len && (map.m_flags & EXT4_MAP_MAPPED))
-				overwrite = 1;
+			if (err == len) {
+			       if (map.m_flags & EXT4_MAP_MAPPED)
+				       overwrite = 1;
+			} else if (nonblocking) {
+				ret = -EAGAIN;
+				goto out;
+			}
 		}
 	}
 
-- 
2.10.2