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.tomoh...@jp.fujitsu.com>
> ---
>  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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