f2fs: add F2FS_GOING_DOWN_METAFLUSH to test power-failure

This patch introduces F2FS_GOING_DOWN_METAFLUSH which flushes meta pages like
SSA blocks and then blocks all the writes.
This can be used by power-failure tests.
Reviewed-by: NChao Yu <chao2.yu@samsung.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -250,6 +250,7 @@ static inline bool __has_cursum_space(struct f2fs_summary_block *sum, int size,
 #define F2FS_GOING_DOWN_FULLSYNC	0x0	/* going down with full sync */
 #define F2FS_GOING_DOWN_METASYNC	0x1	/* going down with metadata */
 #define F2FS_GOING_DOWN_NOSYNC		0x2	/* going down */
+#define F2FS_GOING_DOWN_METAFLUSH	0x3	/* going down with meta flush */
 
 #if defined(__KERNEL__) && defined(CONFIG_COMPAT)
 /*

fs/f2fs/file.c

@@ -1498,6 +1498,10 @@ static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
 	case F2FS_GOING_DOWN_NOSYNC:
 		f2fs_stop_checkpoint(sbi);
 		break;
+	case F2FS_GOING_DOWN_METAFLUSH:
+		sync_meta_pages(sbi, META, LONG_MAX);
+		f2fs_stop_checkpoint(sbi);
+		break;
 	default:
 		return -EINVAL;
 	}