On 2018/05/17 15:39, Qu Wenruo wrote:
> 
> 
> On 2018年05月16日 13:49, 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>
>> ---
>>  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           | 146 
>> +++++++++++++++++++++++++++++++++++++++++++++
>>  include/uapi/linux/btrfs.h |  51 ++++++++++++++++
>>  2 files changed, 197 insertions(+)
>>
>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>> index 48e2ddff32bd..c1c9ae9a937d 100644
>> --- a/fs/btrfs/ioctl.c
>> +++ b/fs/btrfs/ioctl.c
>> @@ -2242,6 +2242,150 @@ 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_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;
>> +
>> +    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);
>> +    root = BTRFS_I(inode)->root->fs_info->tree_root;
>> +
>> +    key.objectid = BTRFS_I(inode)->root->root_key.objectid;
>> +    key.type = BTRFS_ROOT_ITEM_KEY;
>> +    key.offset = 0;
>> +
>> +    ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
> 
> What about just using btrfs_get_fs_root()?
> 
> It would save several lines, and have better error handling along with
> better tree cache.

Here we search ROOT_ITEM of subvolume in root_tree and
I don't think btrfs_get_fs_root() would save lines, right?

Thanks,

> 
> Thanks,
> Qu
> 
>> +    if (ret < 0) {
>> +            goto out;
>> +    } else if (ret > 0) {
>> +            u64 objectid = key.objectid;
>> +
>> +            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 = -ENOENT;
>> +                            goto out;
>> +                    }
>> +            }
>> +
>> +            /* If the subvolume is a snapshot, offset is not zero */
>> +            btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]);
>> +            if (key.objectid != objectid ||
>> +                key.type != BTRFS_ROOT_ITEM_KEY) {
>> +                    ret = -ENOENT;
>> +                    goto out;
>> +            }
>> +    }
>> +
>> +    l = path->nodes[0];
>> +    slot = path->slots[0];
>> +    item_off = btrfs_item_ptr_offset(l, slot);
>> +    item_len = btrfs_item_size_nr(l, slot);
>> +    read_extent_buffer(l, &root_item, item_off, item_len);
>> +
>> +    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.ctime);
>> +    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);
>> +
>> +    btrfs_release_path(path);
>> +    if (key.objectid != BTRFS_FS_TREE_OBJECTID) {
>> +            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 = -ENOENT;
>> +                            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 +5518,8 @@ 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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