[PATCH RFC 4/6] btrfs: implement shutdown ioctl

[Qu Wenruo <wqu@suse.com>]

The shutdown interface should all follow the XFS one, which use magic
'X', and ioctl number 125, with a u32 as flags.

For now btrfs doesn't follow the flags, as there is no traditional
journal in btrfs (the log tree is to mostly speed up fsync).

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/ioctl.c           | 18 ++++++++++++++++++
 include/uapi/linux/btrfs.h |  9 +++++++++
 2 files changed, 27 insertions(+)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 84a516053a8e..1fd7486af851 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -5213,6 +5213,16 @@ static int btrfs_ioctl_subvol_sync(struct btrfs_fs_info *fs_info, void __user *a
 	return 0;
 }
 
+static int btrfs_emergency_shutdown(struct btrfs_fs_info *fs_info, u32 flags)
+{
+	if (flags >= BTRFS_SHUTDOWN_FLAGS_LAST)
+		return -EINVAL;
+
+	/* For now, btrfs do not distinguish the different flags. */
+	btrfs_shutdown(fs_info);
+	return 0;
+}
+
 long btrfs_ioctl(struct file *file, unsigned int
 		cmd, unsigned long arg)
 {
@@ -5368,6 +5378,14 @@ long btrfs_ioctl(struct file *file, unsigned int
 #endif
 	case BTRFS_IOC_SUBVOL_SYNC_WAIT:
 		return btrfs_ioctl_subvol_sync(fs_info, argp);
+	case BTRFS_IOC_SHUTDOWN:
+		u32 flags;
+
+		if (!capable(CAP_SYS_ADMIN))
+			return -EPERM;
+		if (get_user(flags, (__u32 __user *)arg))
+			return -EFAULT;
+		return btrfs_emergency_shutdown(fs_info, flags);
 	}
 
 	return -ENOTTY;
diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index dd02160015b2..8f6324cf15d9 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -1096,6 +1096,12 @@ enum btrfs_err_code {
 	BTRFS_ERROR_DEV_RAID1C4_MIN_NOT_MET,
 };
 
+/* Flags for IOC_SHUTDOWN, should match XFS' flags. */
+#define BTRFS_SHUTDOWN_FLAGS_DEFAULT	0x0
+#define BTRFS_SHUTDOWN_FLAGS_LOGFLUSH	0x1
+#define BTRFS_SHUTDOWN_FLAGS_NOLOGFLUSH	0x2
+#define BTRFS_SHUTDOWN_FLAGS_LAST	0x3
+
 #define BTRFS_IOC_SNAP_CREATE _IOW(BTRFS_IOCTL_MAGIC, 1, \
 				   struct btrfs_ioctl_vol_args)
 #define BTRFS_IOC_DEFRAG _IOW(BTRFS_IOCTL_MAGIC, 2, \
@@ -1217,6 +1223,9 @@ enum btrfs_err_code {
 #define BTRFS_IOC_SUBVOL_SYNC_WAIT _IOW(BTRFS_IOCTL_MAGIC, 65, \
 					struct btrfs_ioctl_subvol_wait)
 
+/* Shutdown ioctl should follow XFS's interfaces, thus not using btrfs magic. */
+#define BTRFS_IOC_SHUTDOWN	_IOR('X', 125, __u32)
+
 #ifdef __cplusplus
 }
 #endif
-- 
2.49.0