f2fs: support fs shutdown

This patch introduces a generic ioctl for fs shutdown, which was used by xfs.

If this shutdown is triggered, filesystem stops any further IOs according to the
following options.

1. FS_GOING_DOWN_FULLSYNC
 : this will flush all the data and dentry blocks, and do checkpoint before
   shutdown.

2. FS_GOING_DOWN_METASYNC
 : this will do checkpoint before shutdown.

3. FS_GOING_DOWN_NOSYNC
 : this will trigger shutdown as is.
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -217,6 +217,15 @@ static inline bool __has_cursum_space(struct f2fs_summary_block *sum, int size,
 #define F2FS_IOC_RELEASE_VOLATILE_WRITE	_IO(F2FS_IOCTL_MAGIC, 4)
 #define F2FS_IOC_ABORT_VOLATILE_WRITE	_IO(F2FS_IOCTL_MAGIC, 5)
 
+/*
+ * should be same as XFS_IOC_GOINGDOWN.
+ * Flags for going down operation used by FS_IOC_GOINGDOWN
+ */
+#define F2FS_IOC_SHUTDOWN	_IOR('X', 125, __u32)	/* Shutdown */
+#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 */
+
 #if defined(__KERNEL__) && defined(CONFIG_COMPAT)
 /*
  * ioctl commands in 32 bit emulation

fs/f2fs/file.c

@@ -1029,6 +1029,41 @@ static int f2fs_ioc_abort_volatile_write(struct file *filp)
 	return ret;
 }
 
+static int f2fs_ioc_shutdown(struct file *filp, unsigned long arg)
+{
+	struct inode *inode = file_inode(filp);
+	struct f2fs_sb_info *sbi = F2FS_I_SB(inode);
+	struct super_block *sb = sbi->sb;
+	__u32 in;
+
+	if (!capable(CAP_SYS_ADMIN))
+		return -EPERM;
+
+	if (get_user(in, (__u32 __user *)arg))
+		return -EFAULT;
+
+	switch (in) {
+	case F2FS_GOING_DOWN_FULLSYNC:
+		sb = freeze_bdev(sb->s_bdev);
+		if (sb && !IS_ERR(sb)) {
+			f2fs_stop_checkpoint(sbi);
+			thaw_bdev(sb->s_bdev, sb);
+		}
+		break;
+	case F2FS_GOING_DOWN_METASYNC:
+		/* do checkpoint only */
+		f2fs_sync_fs(sb, 1);
+		f2fs_stop_checkpoint(sbi);
+		break;
+	case F2FS_GOING_DOWN_NOSYNC:
+		f2fs_stop_checkpoint(sbi);
+		break;
+	default:
+		return -EINVAL;
+	}
+	return 0;
+}
+
 static int f2fs_ioc_fitrim(struct file *filp, unsigned long arg)
 {
 	struct inode *inode = file_inode(filp);
@@ -1078,6 +1113,8 @@ long f2fs_ioctl(struct file *filp, unsigned int cmd, unsigned long arg)
 		return f2fs_ioc_release_volatile_write(filp);
 	case F2FS_IOC_ABORT_VOLATILE_WRITE:
 		return f2fs_ioc_abort_volatile_write(filp);
+	case F2FS_IOC_SHUTDOWN:
+		return f2fs_ioc_shutdown(filp, arg);
 	case FITRIM:
 		return f2fs_ioc_fitrim(filp, arg);
 	default: