[PATCH] f2fs: avoid unused block when dio write in LFS mode

[Daejun Park <daejun7.park@samsung.com>]

This patch addresses the problem that when using LFS mode, unused blocks
may occur in f2fs_map_blocks() during block allocation for dio writes.

If a new section is allocated during block allocation, it will not be
included in the map struct by map_is_mergeable() if the LBA of the
allocated block is not contiguous. However, the block already allocated
in this process will remain unused due to the LFS mode.

This patch avoids the possibility of unused blocks by escaping
f2fs_map_blocks() when allocating the last block in a section.

Signed-off-by: Daejun Park <daejun7.park@samsung.com>
---
 fs/f2fs/data.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/fs/f2fs/data.c b/fs/f2fs/data.c
index b6dcb3bcaef7..b27a3f448f32 100644
--- a/fs/f2fs/data.c
+++ b/fs/f2fs/data.c
@@ -1711,6 +1711,19 @@ int f2fs_map_blocks(struct inode *inode, struct f2fs_map_blocks *map, int flag)
 		dn.ofs_in_node = end_offset;
 	}
 
+	if (flag == F2FS_GET_BLOCK_DIO && f2fs_lfs_mode(sbi)) {
+		int segno = GET_SEGNO(sbi, blkaddr);
+		bool last_seg, last_blk;
+
+		last_seg = !((segno + 1) % SEGS_PER_SEC(sbi));
+		last_blk = (f2fs_usable_blks_in_seg(sbi, segno) - 1) ==
+				GET_BLKOFF_FROM_SEG0(sbi, blkaddr);
+
+		/* LBA of the next block to be allocated may not be contiguous. */
+		if (last_seg && last_blk)
+			goto sync_out;
+	}
+
 	if (pgofs >= end)
 		goto sync_out;
 	else if (dn.ofs_in_node < end_offset)
-- 
2.25.1