On 2018/05/18 11:54, Tomohiro Misono wrote:
> Add new unprivileged ioctl BTRFS_IOC_GET_SUBVOL_INFO which returns
> the information of subvolume containing this inode.
> (i.e. returns the information in ROOT_ITEM and ROOT_BACKREF.)
>
> Signed-off-by: Tomohiro Misono <misono.tomohiro@xxxxxxxxxxxxxx>
> ---
> v5 -> v6
> - Use brfs_read_fs_root_no_name() to get subvolume root and simplify
> code
> v4 -> v5
> - Update error handling of btrfs_next_leaf() to cover all cases
> - Return error if ROOT_BACKREF is not found (except top-level)
>
> fs/btrfs/ioctl.c | 125 +++++++++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/btrfs.h | 51 ++++++++++++++++++
> 2 files changed, 176 insertions(+)
>
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 48e2ddff32bd..31af6e91c614 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -2242,6 +2242,129 @@ static noinline int btrfs_ioctl_ino_lookup(struct file *file,
> return ret;
> }
>
> +/* Get the subvolume information in BTRFS_ROOT_ITEM and BTRFS_ROOT_BACKREF */
> +static noinline int btrfs_ioctl_get_subvol_info(struct file *file,
> + void __user *argp)
> +{
> + struct btrfs_ioctl_get_subvol_info_args *subvol_info;
> + struct btrfs_fs_info *fs_info;
> + struct btrfs_root *root;
> + struct btrfs_path *path;
> + struct btrfs_key key;
> +
> + struct btrfs_root_item *root_item;
> + struct btrfs_root_ref *rref;
> + struct extent_buffer *l;
> + int slot;
> +
> + unsigned long item_off;
> + unsigned long item_len;
> +
> + struct inode *inode;
> + int ret = 0;
> +
> + path = btrfs_alloc_path();
> + if (!path)
> + return -ENOMEM;
> +
> + subvol_info = kzalloc(sizeof(*subvol_info), GFP_KERNEL);
> + if (!subvol_info) {
> + btrfs_free_path(path);
> + return -ENOMEM;
> + }
> +
> + inode = file_inode(file);
> + fs_info = BTRFS_I(inode)->root->fs_info;
> +
> + /* Get root_item of inode's subvolume */
> + key.objectid = BTRFS_I(inode)->root->root_key.objectid;
> + key.type = BTRFS_ROOT_ITEM_KEY;
> + key.offset = (u64)-1;
> + root = btrfs_read_fs_root_no_name(fs_info, &key);
> + if (IS_ERR(root)) {
> + ret = PTR_ERR(root);
> + goto out;
> + }
> + root_item = &root->root_item;
> +
> + subvol_info->id = key.objectid;
> +
> + subvol_info->generation = btrfs_root_generation(root_item);
> + subvol_info->flags = btrfs_root_flags(root_item);
> +
> + memcpy(subvol_info->uuid, root_item->uuid, BTRFS_UUID_SIZE);
> + memcpy(subvol_info->parent_uuid, root_item->parent_uuid,
> + BTRFS_UUID_SIZE);
> + memcpy(subvol_info->received_uuid, root_item->received_uuid,
> + BTRFS_UUID_SIZE);
> +
> + subvol_info->ctransid = btrfs_root_ctransid(root_item);
> + subvol_info->ctime.sec = btrfs_stack_timespec_sec(&root_item->otime);
obviously ->ctime, sorry for messed up.
> + subvol_info->ctime.nsec = btrfs_stack_timespec_nsec(&root_item->ctime);
> +
> + subvol_info->otransid = btrfs_root_otransid(root_item);
> + subvol_info->otime.sec = btrfs_stack_timespec_sec(&root_item->otime);
> + subvol_info->otime.nsec = btrfs_stack_timespec_nsec(&root_item->otime);
> +
> + subvol_info->stransid = btrfs_root_stransid(root_item);
> + subvol_info->stime.sec = btrfs_stack_timespec_sec(&root_item->stime);
> + subvol_info->stime.nsec = btrfs_stack_timespec_nsec(&root_item->stime);
> +
> + subvol_info->rtransid = btrfs_root_rtransid(root_item);
> + subvol_info->rtime.sec = btrfs_stack_timespec_sec(&root_item->rtime);
> + subvol_info->rtime.nsec = btrfs_stack_timespec_nsec(&root_item->rtime);
> +
> + if (key.objectid != BTRFS_FS_TREE_OBJECTID) {
> + /* Search root tree for ROOT_BACKREF of this subvolume */
> + root = fs_info->tree_root;
> +
> + key.type = BTRFS_ROOT_BACKREF_KEY;
> + key.offset = 0;
> + ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
> + if (ret < 0) {
> + goto out;
> + } else if (path->slots[0] >=
> + btrfs_header_nritems(path->nodes[0])) {
> + ret = btrfs_next_leaf(root, path);
> + if (ret < 0) {
> + goto out;
> + } else if (ret > 0) {
> + ret = -EUCLEAN;
> + goto out;
> + }
> + }
> +
> + l = path->nodes[0];
> + slot = path->slots[0];
> + btrfs_item_key_to_cpu(l, &key, slot);
> + if (key.objectid == subvol_info->id &&
> + key.type == BTRFS_ROOT_BACKREF_KEY) {
> + subvol_info->parent_id = key.offset;
> +
> + rref = btrfs_item_ptr(l, slot, struct btrfs_root_ref);
> + subvol_info->dirid = btrfs_root_ref_dirid(l, rref);
> +
> + item_off = btrfs_item_ptr_offset(l, slot)
> + + sizeof(struct btrfs_root_ref);
> + item_len = btrfs_item_size_nr(l, slot)
> + - sizeof(struct btrfs_root_ref);
> + read_extent_buffer(l, subvol_info->name,
> + item_off, item_len);
> + } else {
> + ret = -ENOENT;
> + goto out;
> + }
> + }
> +
> + if (copy_to_user(argp, subvol_info, sizeof(*subvol_info)))
> + ret = -EFAULT;
> +
> +out:
> + kzfree(subvol_info);
> + btrfs_free_path(path);
> + return ret;
> +}
> +
> static noinline int btrfs_ioctl_snap_destroy(struct file *file,
> void __user *arg)
> {
> @@ -5374,6 +5497,8 @@ long btrfs_ioctl(struct file *file, unsigned int
> return btrfs_ioctl_get_features(file, argp);
> case BTRFS_IOC_SET_FEATURES:
> return btrfs_ioctl_set_features(file, argp);
> + case BTRFS_IOC_GET_SUBVOL_INFO:
> + return btrfs_ioctl_get_subvol_info(file, argp);
> }
>
> return -ENOTTY;
> diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h
> index c8d99b9ca550..02cd1f1994e8 100644
> --- a/include/uapi/linux/btrfs.h
> +++ b/include/uapi/linux/btrfs.h
> @@ -725,6 +725,55 @@ struct btrfs_ioctl_send_args {
> __u64 reserved[4]; /* in */
> };
>
> +struct btrfs_ioctl_get_subvol_info_args {
> + /* All field is out */
> + /* Id of this subvolume */
> + __u64 id;
> + /* Name of this subvolume, used to get the real name at mount point */
> + char name[BTRFS_VOL_NAME_MAX + 1];
> + /*
> + * Id of the subvolume which contains this subvolume.
> + * Zero for top-level subvolume or deleted subvolume
> + */
> + __u64 parent_id;
> + /*
> + * Inode number of the directory which contains this subvolume.
> + * Zero for top-level subvolume or deleted subvolume
> + */
> + __u64 dirid;
> +
> + /* Latest transaction id of this subvolume */
> + __u64 generation;
> + /* Flags of this subvolume */
> + __u64 flags;
> +
> + /* uuid of this subvolume */
> + __u8 uuid[BTRFS_UUID_SIZE];
> + /*
> + * uuid of the subvolume of which this subvolume is a snapshot.
> + * All zero for non-snapshot subvolume
> + */
> + __u8 parent_uuid[BTRFS_UUID_SIZE];
> + /*
> + * uuid of the subvolume from which this subvolume is received.
> + * All zero for non-received subvolume
> + */
> + __u8 received_uuid[BTRFS_UUID_SIZE];
> +
> + /* Transaction id indicates when change/create/send/receive happens */
> + __u64 ctransid;
> + __u64 otransid;
> + __u64 stransid;
> + __u64 rtransid;
> + /* Time corresponds to c/o/s/rtransid */
> + struct btrfs_ioctl_timespec ctime;
> + struct btrfs_ioctl_timespec otime;
> + struct btrfs_ioctl_timespec stime;
> + struct btrfs_ioctl_timespec rtime;
> +
> + __u64 reserved[8];
> +};
> +
> /* Error codes as returned by the kernel */
> enum btrfs_err_code {
> BTRFS_ERROR_DEV_RAID1_MIN_NOT_MET = 1,
> @@ -843,5 +892,7 @@ enum btrfs_err_code {
> struct btrfs_ioctl_vol_args_v2)
> #define BTRFS_IOC_LOGICAL_INO_V2 _IOWR(BTRFS_IOCTL_MAGIC, 59, \
> struct btrfs_ioctl_logical_ino_args)
> +#define BTRFS_IOC_GET_SUBVOL_INFO _IOR(BTRFS_IOCTL_MAGIC, 60, \
> + struct btrfs_ioctl_get_subvol_info_args)
>
> #endif /* _UAPI_LINUX_BTRFS_H */
>
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