f2fs: split IO error injection according to RW

This patch adds to support injecting error for write IO, this can simulate
IO error like fail_make_request or dm_flakey does.

Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/Documentation/filesystems/f2fs.txt b/Documentation/filesystems/f2fs.txt
index d9a0f69..e62809e 100644
--- a/Documentation/filesystems/f2fs.txt
+++ b/Documentation/filesystems/f2fs.txt
@@ -171,9 +171,10 @@
                        FAULT_DIR_DEPTH		0x000000100
                        FAULT_EVICT_INODE	0x000000200
                        FAULT_TRUNCATE		0x000000400
-                       FAULT_IO			0x000000800
+                       FAULT_READ_IO		0x000000800
                        FAULT_CHECKPOINT		0x000001000
                        FAULT_DISCARD		0x000002000
+                       FAULT_WRITE_IO		0x000004000
 mode=%s                Control block allocation mode which supports "adaptive"
                        and "lfs". In "lfs" mode, there should be no random
                        writes towards main area.