> -----Original Message-----
> From: linux-btrfs-ow...@vger.kernel.org 
> [mailto:linux-btrfs-ow...@vger.kernel.org] On Behalf Of Tomohiro Misono
> Sent: Friday, May 18, 2018 10:55 AM
> To: linux-btrfs@vger.kernel.org
> Subject: [PATCH v6 2/3] btrfs: Add unprivileged ioctl which returns 
> subvolume's ROOT_REF
> 
> Add unprivileged ioctl BTRFS_IOC_GET_SUBVOL_ROOTREF which returns ROOT_REF 
> information of the subvolume containing this inode
> except the subvolume name (this is because to prevent potential name leak). 
> The subvolume name will be gained by user version of
> ino_lookup ioctl (BTRFS_IOC_INO_LOOKUP_USER) which also performs permission 
> check.
> 
> The min id of root ref's subvolume to be searched is specified by @min_id in 
> struct btrfs_ioctl_get_subvol_rootref_args. After the search
> ends, @min_id is set to the last searched root ref's subvolid + 1. Also, if 
> there are more root refs than
> BTRFS_MAX_ROOTREF_BUFFER_NUM, -EOVERFLOW is returned. Therefore the caller 
> can just call this ioctl again without changing the
> argument to continue search.
> 
> Reviewed-by: Qu Wenruo <w...@suse.com>
> Signed-off-by: Tomohiro Misono <misono.tomoh...@jp.fujitsu.com>
> ---
>  v4 -> v5
>     - Update error handling of btrfs_next_leaf() to cover all cases
>     - Use btrfs_next_item() to reduce the call of btrfs_search_slot()
> 
>  fs/btrfs/ioctl.c           | 102 
> +++++++++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/btrfs.h |  16 +++++++
>  2 files changed, 118 insertions(+)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 
> 31af6e91c614..463ddedd90da 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -2365,6 +2365,106 @@ static noinline int 
> btrfs_ioctl_get_subvol_info(struct file *file,
>       return ret;
>  }
> 
> +/*
> + * Return ROOT_REF information of the subvolume containing this inode
> + * except the subvolume name.
> + */
> +static noinline int btrfs_ioctl_get_subvol_rootref(struct file *file,
> +                                        void __user *argp)
> +{
> +     struct btrfs_ioctl_get_subvol_rootref_args *rootrefs;
> +     struct btrfs_root_ref *rref;
> +     struct btrfs_root *root;
> +     struct btrfs_path *path;
> +     struct btrfs_key key;
> +
> +     struct extent_buffer *l;
> +     int slot;
> +
> +     struct inode *inode;
> +     int ret;
> +     u64 objectid;
> +     u8 found;
> +
> +     path = btrfs_alloc_path();
> +     if (!path)
> +             return -ENOMEM;
> +
> +     rootrefs = memdup_user(argp, sizeof(*rootrefs));
> +     if (!rootrefs) {
> +             btrfs_free_path(path);
> +             return -ENOMEM;
> +     }
> +
> +     inode = file_inode(file);
> +     root = BTRFS_I(inode)->root->fs_info->tree_root;
> +     objectid = BTRFS_I(inode)->root->root_key.objectid;
> +
> +     key.objectid = objectid;
> +     key.type = BTRFS_ROOT_REF_KEY;
> +     key.offset = rootrefs->min_id;
> +     found = 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;
> +             }
> +     }
> +     while (1) {
> +             l = path->nodes[0];
> +             slot = path->slots[0];
> +
> +             btrfs_item_key_to_cpu(l, &key, slot);
> +             if (key.objectid != objectid ||
> +                 key.type != BTRFS_ROOT_REF_KEY) {
> +                     ret = 0;
> +                     goto out;
> +             }
> +
> +             if (found == BTRFS_MAX_ROOTREF_BUFFER_NUM) {
> +                     ret = -EOVERFLOW;
> +                     goto out;
> +             }
> +
> +             rref = btrfs_item_ptr(l, slot, struct btrfs_root_ref);
> +             rootrefs->rootref[found].subvolid = key.offset;
> +             rootrefs->rootref[found].dirid =
> +                               btrfs_root_ref_dirid(l, rref);
> +             found++;
> +
> +             ret = btrfs_next_item(root, path);
> +             if (ret < 0) {
> +                     goto out;
> +             } else if (ret > 0) {
> +                     ret = -EUCLEAN;
> +                     goto out;
> +             }
> +     }
> +
> +out:
> +     if (!ret || ret == -EOVERFLOW) {
> +             rootrefs->num_items = found;
> +             /* update min_id for next search */
> +             if (found)
> +                     rootrefs->min_id =
> +                             rootrefs->rootref[found - 1].subvolid + 1;
> +             if (copy_to_user(argp, rootrefs, sizeof(*rootrefs)))
> +                     ret = -EFAULT;
> +     }
> +
> +     btrfs_free_path(path);
> +     kfree(rootrefs);
> +     return ret;
> +}
> +
>  static noinline int btrfs_ioctl_snap_destroy(struct file *file,
>                                            void __user *arg)
>  {
> @@ -5499,6 +5599,8 @@ long btrfs_ioctl(struct file *file, unsigned int
>               return btrfs_ioctl_set_features(file, argp);
>       case BTRFS_IOC_GET_SUBVOL_INFO:
>               return btrfs_ioctl_get_subvol_info(file, argp);
> +     case BTRFS_IOC_GET_SUBVOL_ROOTREF:
> +             return btrfs_ioctl_get_subvol_rootref(file, argp);
>       }
> 
>       return -ENOTTY;
> diff --git a/include/uapi/linux/btrfs.h b/include/uapi/linux/btrfs.h index 
> 02cd1f1994e8..b6633f5d4847 100644
> --- a/include/uapi/linux/btrfs.h
> +++ b/include/uapi/linux/btrfs.h
> @@ -774,6 +774,20 @@ struct btrfs_ioctl_get_subvol_info_args {
>       __u64 reserved[8];
>  };
> 
> +#define BTRFS_MAX_ROOTREF_BUFFER_NUM 255 struct
> +btrfs_ioctl_get_subvol_rootref_args {
> +             /* in/out, min id of rootref's subvolid to be searched */
> +             __u64 min_id;
> +             /* out */
> +             struct {
> +                     __u64 subvolid;
> +                     __u64 dirid;
> +             } rootref[BTRFS_MAX_ROOTREF_BUFFER_NUM];
> +             /* out, number of found items */
> +             __u8 num_items;
> +             __u8 align[7];
> +};
> +
>  /* Error codes as returned by the kernel */  enum btrfs_err_code {
>       BTRFS_ERROR_DEV_RAID1_MIN_NOT_MET = 1, @@ -894,5 +908,7 @@ enum 
> btrfs_err_code {
>                                       struct btrfs_ioctl_logical_ino_args)  
> #define BTRFS_IOC_GET_SUBVOL_INFO
> _IOR(BTRFS_IOCTL_MAGIC, 60, \
>                               struct btrfs_ioctl_get_subvol_info_args)
> +#define BTRFS_IOC_GET_SUBVOL_ROOTREF _IOWR(BTRFS_IOCTL_MAGIC, 61, \
> +                             struct btrfs_ioctl_get_subvol_rootref_args)
> 
>  #endif /* _UAPI_LINUX_BTRFS_H */
> --

Looks good to me.
Reviewed-by: Gu Jinxiang <g...@cn.fujitsu.com>

> 2.14.3
> 
> 
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