f2fs: add nowait aio support

This patch adds nowait aio support[1].

Return EAGAIN if any of the following checks fail for direct I/O:
  - i_rwsem is not lockable
  - Blocks are not allocated at the write location

And xfstests generic/471 is passed.

 [1]: 6be96d "Introduce RWF_NOWAIT and FMODE_AIO_NOWAIT"

Signed-off-by: Hyunchul Lee <cheol.lee@lge.com>
Reviewed-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -839,13 +839,6 @@ alloc:
 	return 0;
 }
 
-static inline bool __force_buffered_io(struct inode *inode, int rw)
-{
-	return (f2fs_encrypted_file(inode) ||
-			(rw == WRITE && test_opt(F2FS_I_SB(inode), LFS)) ||
-			F2FS_I_SB(inode)->s_ndevs);
-}
-
 int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct inode *inode = file_inode(iocb->ki_filp);
@@ -877,7 +870,7 @@ int f2fs_preallocate_blocks(struct kiocb *iocb, struct iov_iter *from)
 
 	if (direct_io) {
 		map.m_seg_type = rw_hint_to_seg_type(iocb->ki_hint);
-		flag = __force_buffered_io(inode, WRITE) ?
+		flag = f2fs_force_buffered_io(inode, WRITE) ?
 					F2FS_GET_BLOCK_PRE_AIO :
 					F2FS_GET_BLOCK_PRE_DIO;
 		goto map_blocks;
@@ -1121,6 +1114,31 @@ out:
 	return err;
 }
 
+bool f2fs_overwrite_io(struct inode *inode, loff_t pos, size_t len)
+{
+	struct f2fs_map_blocks map;
+	block_t last_lblk;
+	int err;
+
+	if (pos + len > i_size_read(inode))
+		return false;
+
+	map.m_lblk = F2FS_BYTES_TO_BLK(pos);
+	map.m_next_pgofs = NULL;
+	map.m_next_extent = NULL;
+	map.m_seg_type = NO_CHECK_TYPE;
+	last_lblk = F2FS_BLK_ALIGN(pos + len);
+
+	while (map.m_lblk < last_lblk) {
+		map.m_len = last_lblk - map.m_lblk;
+		err = f2fs_map_blocks(inode, &map, 0, F2FS_GET_BLOCK_DEFAULT);
+		if (err || map.m_len == 0)
+			return false;
+		map.m_lblk += map.m_len;
+	}
+	return true;
+}
+
 static int __get_data_block(struct inode *inode, sector_t iblock,
 			struct buffer_head *bh, int create, int flag,
 			pgoff_t *next_pgofs, int seg_type)
@@ -2306,7 +2324,7 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 	if (err)
 		return err;
 
-	if (__force_buffered_io(inode, rw))
+	if (f2fs_force_buffered_io(inode, rw))
 		return 0;
 
 	trace_f2fs_direct_IO_enter(inode, offset, count, rw);
@@ -2314,7 +2332,15 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 	if (rw == WRITE && whint_mode == WHINT_MODE_OFF)
 		iocb->ki_hint = WRITE_LIFE_NOT_SET;
 
-	down_read(&F2FS_I(inode)->dio_rwsem[rw]);
+	if (!down_read_trylock(&F2FS_I(inode)->dio_rwsem[rw])) {
+		if (iocb->ki_flags & IOCB_NOWAIT) {
+			iocb->ki_hint = hint;
+			err = -EAGAIN;
+			goto out;
+		}
+		down_read(&F2FS_I(inode)->dio_rwsem[rw]);
+	}
+
 	err = blockdev_direct_IO(iocb, inode, iter, get_data_block_dio);
 	up_read(&F2FS_I(inode)->dio_rwsem[rw]);
 
@@ -2330,6 +2356,7 @@ static ssize_t f2fs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 		}
 	}
 
+out:
 	trace_f2fs_direct_IO_exit(inode, offset, count, rw, err);
 
 	return err;