btrfs: add new BTRFS_IOC_SNAP_DESTROY_V2 ioctl

This ioctl will be responsible for deleting a subvolume using its id.
This can be used when a system has a file system mounted from a
subvolume, rather than the root file system, like below:

/
@subvol1/
@subvol2/
@subvol_default/

If only @subvol_default is mounted, we have no path to reach @subvol1
and @subvol2, thus no way to delete them. Current subvolume delete ioctl
takes a file handle point as argument, and if @subvol_default is
mounted, we can't reach @subvol1 and @subvol2 from the same mount point.

This patch introduces a new ioctl BTRFS_IOC_SNAP_DESTROY_V2 that takes
the extended structure with flags to allow to delete subvolume using
subvolid.

Now, we can use this new ioctl specifying the subvolume id and refer to
the same mount point. It doesn't matter which subvolume was mounted,
since we can reach to the desired one using the subvolume id, and then
delete it.

The full path to the subvolume id is resolved internally and access is
verified as if the subvolume was accessed by path.

The volume args v2 structure is extended to use the existing union for
subvolume id specification, that's valid in case the
BTRFS_SUBVOL_SPEC_BY_ID is set.

Signed-off-by: Marcos Paulo de Souza <mpdesouza@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
index 49ed71df5e94..b5f3ea36d3cb 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -42,11 +42,14 @@ struct btrfs_ioctl_vol_args {
 
 #define BTRFS_DEVICE_SPEC_BY_ID		(1ULL << 3)
 
+#define BTRFS_SUBVOL_SPEC_BY_ID	(1ULL << 4)
+
 #define BTRFS_VOL_ARG_V2_FLAGS_SUPPORTED		\
 			(BTRFS_SUBVOL_CREATE_ASYNC |	\
 			BTRFS_SUBVOL_RDONLY |		\
 			BTRFS_SUBVOL_QGROUP_INHERIT |	\
-			BTRFS_DEVICE_SPEC_BY_ID)
+			BTRFS_DEVICE_SPEC_BY_ID |	\
+			BTRFS_SUBVOL_SPEC_BY_ID)
 
 #define BTRFS_FSID_SIZE 16
 #define BTRFS_UUID_SIZE 16
@@ -117,6 +120,10 @@ struct btrfs_ioctl_qgroup_limit_args {
 	 BTRFS_SUBVOL_RDONLY |						\
 	 BTRFS_SUBVOL_QGROUP_INHERIT)
 
+/* Supported flags for BTRFS_IOC_SNAP_DESTROY_V2 */
+#define BTRFS_SUBVOL_DELETE_ARGS_MASK					\
+	(BTRFS_SUBVOL_SPEC_BY_ID)
+
 struct btrfs_ioctl_vol_args_v2 {
 	__s64 fd;
 	__u64 transid;
@@ -131,6 +138,7 @@ struct btrfs_ioctl_vol_args_v2 {
 	union {
 		char name[BTRFS_SUBVOL_NAME_MAX + 1];
 		__u64 devid;
+		__u64 subvolid;
 	};
 };
 
@@ -959,5 +967,7 @@ enum btrfs_err_code {
 				struct btrfs_ioctl_get_subvol_rootref_args)
 #define BTRFS_IOC_INO_LOOKUP_USER _IOWR(BTRFS_IOCTL_MAGIC, 62, \
 				struct btrfs_ioctl_ino_lookup_user_args)
+#define BTRFS_IOC_SNAP_DESTROY_V2 _IOW(BTRFS_IOCTL_MAGIC, 63, \
+				struct btrfs_ioctl_vol_args_v2)
 
 #endif /* _UAPI_LINUX_BTRFS_H */