f2fs: add an ioctl() to explicitly trigger fsck later

This adds an option in ioctl(F2FS_IOC_SHUTDOWN) in order to trigger fsck by
setting a NEED_FSCK flag.

Generally, shutdown is used for the test to validate filesystem consistency, and
setting NEED_FSCK flag can be used for Android to trigger fsck.f2fs at boot time
explicitly so that we could measure the elapsed time as well as force filesystem
check.

Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -417,6 +417,7 @@ static inline bool __has_cursum_space(struct f2fs_journal *journal,
 #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 */
+#define F2FS_GOING_DOWN_NEED_FSCK	0x4	/* going down to trigger fsck */
 
 #if defined(__KERNEL__) && defined(CONFIG_COMPAT)
 /*