[PATCH] btrfs: extend BTRFS_IOC_SNAP_CREATE_V2 to snapshot by subvolid

Jeff Mahoney
2014-03-24T23:58:37Z

The BTRFS_IOC_SNAP_CREATE_V2 ioctl is limited by requiring that a file
descriptor be passed in order to create the snapshot. This means that
snapshots may only be created of trees that are available in the mounted
namespace. We have a need to create snapshots from subvolumes outside
of the namespace. This is already possible by mounting the numbered
subvolume by ID on a separate mount point, creating the snapshot, and
unmounting it. That's a tedious and unnecessary process since the ioctl
can be extended so easily.

This patch adds a new BTRFS_SUBVOL_CREATE_SUBVOLID flag that instructs
the ioctl to use the fd argument (which is now a union) as a subvolume
id instead. The subvolume ID is used to look up the root and instantiate
the inode so proper permission checking takes place.

Signed-off-by: Jeff Mahoney <jeffm@suse.com>
---
fs/btrfs/ioctl.c | 77 +++++++++++++++++++++++++++++++++++----------
include/uapi/linux/btrfs.h | 6 ++-
2 files changed, 65 insertions(+), 18 deletions(-)

--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1535,8 +1535,8 @@ out:
}

static noinline int btrfs_ioctl_snap_create_transid(struct file *file,
- char *name, unsigned long fd, int subvol,
- u64 *transid, bool readonly,
+ char *name, struct inode *src_inode,
+ int subvol, u64 *transid, bool readonly,
struct btrfs_qgroup_inherit *inherit)
{
int namelen;
@@ -1562,14 +1562,6 @@ static noinline int btrfs_ioctl_snap_cre
ret = btrfs_mksubvol(&file->f_path, name, namelen,
NULL, transid, readonly, inherit);
} else {
- struct fd src = fdget(fd);
- struct inode *src_inode;
- if (!src.file) {
- ret = -EINVAL;
- goto out_drop_write;
- }
-
- src_inode = file_inode(src.file);
if (src_inode->i_sb != file_inode(file)->i_sb) {
btrfs_info(BTRFS_I(src_inode)->root->fs_info,
"Snapshot src from another FS");
@@ -1585,7 +1577,6 @@ static noinline int btrfs_ioctl_snap_cre
BTRFS_I(src_inode)->root,
transid, readonly, inherit);
}
- fdput(src);
}
out_drop_write:
mnt_drop_write_file(file);
@@ -1597,6 +1588,7 @@ static noinline int btrfs_ioctl_snap_cre
void __user *arg, int subvol)
{
struct btrfs_ioctl_vol_args *vol_args;
+ struct fd src;
int ret;

vol_args = memdup_user(arg, sizeof(*vol_args));
@@ -1604,10 +1596,19 @@ static noinline int btrfs_ioctl_snap_cre
return PTR_ERR(vol_args);
vol_args->name[BTRFS_PATH_NAME_MAX] = '\0';

+ if (!subvol) {
+ src = fdget(vol_args->fd);
+ if (!src.file) {
+ ret = -EINVAL;
+ goto out_free;
+ }
+ }
+
ret = btrfs_ioctl_snap_create_transid(file, vol_args->name,
- vol_args->fd, subvol,
+ file_inode(src.file), subvol,
NULL, false, NULL);
-
+ fdput(src);
+out_free:
kfree(vol_args);
return ret;
}
@@ -1621,6 +1622,8 @@ static noinline int btrfs_ioctl_snap_cre
u64 *ptr = NULL;
bool readonly = false;
struct btrfs_qgroup_inherit *inherit = NULL;
+ struct fd src;
+ struct inode *src_inode = NULL;

vol_args = memdup_user(arg, sizeof(*vol_args));
if (IS_ERR(vol_args))
@@ -1629,7 +1632,7 @@ static noinline int btrfs_ioctl_snap_cre

if (vol_args->flags &
~(BTRFS_SUBVOL_CREATE_ASYNC | BTRFS_SUBVOL_RDONLY |
- BTRFS_SUBVOL_QGROUP_INHERIT)) {
+ BTRFS_SUBVOL_QGROUP_INHERIT|BTRFS_SUBVOL_CREATE_SUBVOLID)) {
ret = -EOPNOTSUPP;
goto out;
}
@@ -1650,9 +1653,49 @@ static noinline int btrfs_ioctl_snap_cre
}
}

- ret = btrfs_ioctl_snap_create_transid(file, vol_args->name,
- vol_args->fd, subvol, ptr,
- readonly, inherit);
+ if (!subvol) {
+ if (vol_args->flags & BTRFS_SUBVOL_CREATE_SUBVOLID) {
+ struct super_block *sb = file_inode(file)->i_sb;
+ struct btrfs_root *root;
+ struct btrfs_key location = {
+ .objectid = vol_args->subvolid,
+ .offset = -1,
+ .type = BTRFS_ROOT_ITEM_KEY,
+ };
+
+ root = btrfs_get_fs_root(btrfs_sb(sb), &location, true);
+ if (IS_ERR(root)) {
+ ret = PTR_ERR(root);
+ goto out;
+ }
+
+ location.objectid = btrfs_root_dirid(&root->root_item);
+ location.type = BTRFS_INODE_ITEM_KEY;
+ location.offset = 0;
+ src_inode = btrfs_iget(sb, &location, root, NULL);
+ if (IS_ERR(src_inode)) {
+ ret = PTR_ERR(src_inode);
+ goto out;
+ }
+ } else {
+ src = fdget(vol_args->fd);
+ if (!src.file) {
+ ret = -EINVAL;
+ goto out;
+ }
+ src_inode = file_inode(src.file);
+ }
+ }
+
+ ret = btrfs_ioctl_snap_create_transid(file, vol_args->name, src_inode,
+ subvol, ptr, readonly, inherit);
+
+ if (!subvol) {
+ if (vol_args->flags & BTRFS_SUBVOL_CREATE_SUBVOLID)
+ iput(src_inode);
+ else
+ fdput(src);
+ }

if (ret == 0 && ptr &&
copy_to_user(arg +
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -36,6 +36,7 @@ struct btrfs_ioctl_vol_args {
#define BTRFS_SUBVOL_CREATE_ASYNC (1ULL << 0)
#define BTRFS_SUBVOL_RDONLY (1ULL << 1)
#define BTRFS_SUBVOL_QGROUP_INHERIT (1ULL << 2)
+#define BTRFS_SUBVOL_CREATE_SUBVOLID (1ULL << 3)
#define BTRFS_FSID_SIZE 16
#define BTRFS_UUID_SIZE 16

@@ -65,7 +66,10 @@ struct btrfs_ioctl_qgroup_limit_args {

#define BTRFS_SUBVOL_NAME_MAX 4039
struct btrfs_ioctl_vol_args_v2 {
- __s64 fd;
+ union {
+ __s64 fd;
+ __u64 subvolid;
+ };
__u64 transid;
__u64 flags;
union {

--
Jeff Mahoney
SUSE Labs