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>
diff --git a/fs/f2fs/f2fs.h b/fs/f2fs/f2fs.h
index d60cf41..181cf85 100644
--- a/fs/f2fs/f2fs.h
+++ b/fs/f2fs/f2fs.h
@@ -419,6 +419,7 @@
 #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)
 /*
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index 10d9336..e57b073 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -1962,6 +1962,13 @@
 		f2fs_stop_checkpoint(sbi, false);
 		set_sbi_flag(sbi, SBI_IS_SHUTDOWN);
 		break;
+	case F2FS_GOING_DOWN_NEED_FSCK:
+		set_sbi_flag(sbi, SBI_NEED_FSCK);
+		/* do checkpoint only */
+		ret = f2fs_sync_fs(sb, 1);
+		if (ret)
+			goto out;
+		break;
 	default:
 		ret = -EINVAL;
 		goto out;