[1/2] btrfs: Add unprivileged subvolume search ioctl
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Message ID 62ce1ddf-a7cd-f770-b4c8-5d47b8d4d31d@jp.fujitsu.com
State New
Headers show

Commit Message

Misono Tomohiro March 6, 2018, 8:30 a.m. UTC
Add new unprivileged ioctl (BTRFS_IOC_GET_SUBVOL_INFO) which searches
and returns only subvolume related item (ROOT_ITEM/ROOT_BACKREF/ROOT_REF)
from root tree. The arguments of this ioctl are the same as treesearch
ioctl and can be used like treesearch ioctl.

Since treesearch ioctl requires root privilege, this ioctl is needed
to allow normal users to call "btrfs subvolume list/show" etc.

Note that the subvolume name in ROOT_BACKREF/ROOT_REF will not be copied to
prevent potential name leak. The name can be obtained by calling
user version's ino_lookup ioctl (BTRFS_IOC_INO_LOOKUP_USER).

Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
---
 fs/btrfs/ioctl.c           | 254 +++++++++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/btrfs.h |   2 +
 2 files changed, 256 insertions(+)

Comments

Goffredo Baroncelli March 6, 2018, 8:29 p.m. UTC | #1
On 03/06/2018 09:30 AM, Misono, Tomohiro wrote:
> Add new unprivileged ioctl (BTRFS_IOC_GET_SUBVOL_INFO) which searches
> and returns only subvolume related item (ROOT_ITEM/ROOT_BACKREF/ROOT_REF)
> from root tree. The arguments of this ioctl are the same as treesearch
> ioctl and can be used like treesearch ioctl.

Is it a pro ? The treesearch ioctl is tightly coupled to the btrfs internal structure, this means that if we would change the btrfs internal structure, we have to update all the clients of this api. For the treesearch it is an acceptable compromise between flexibility and speed of developing. But for a more specialized API, I think that it would make sense to provide a less coupled api to the internal structure.

Below some comments


> 
> Since treesearch ioctl requires root privilege, this ioctl is needed
> to allow normal users to call "btrfs subvolume list/show" etc.
> 
> Note that the subvolume name in ROOT_BACKREF/ROOT_REF will not be copied to
> prevent potential name leak. The name can be obtained by calling
> user version's ino_lookup ioctl (BTRFS_IOC_INO_LOOKUP_USER).
> 
> Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
> ---
>  fs/btrfs/ioctl.c           | 254 +++++++++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/btrfs.h |   2 +
>  2 files changed, 256 insertions(+)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 111ee282b777..1dba309dce31 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -1921,6 +1921,28 @@ static noinline int key_in_sk(struct btrfs_key *key,
>  	return 1;
>  }
>  
> +/*
> + * check if key is in sk and subvolume related range
> + */
> +static noinline int key_in_sk_and_subvol(struct btrfs_key *key,
> +			      struct btrfs_ioctl_search_key *sk)
> +{
> +	int ret;
> +
> +	ret = key_in_sk(key, sk);
> +	if (!ret)
> +		return 0;
> +
> +	if ((key->objectid == BTRFS_FS_TREE_OBJECTID ||
> +		(key->objectid >= BTRFS_FIRST_FREE_OBJECTID &&
> +		 key->objectid <= BTRFS_LAST_FREE_OBJECTID)) &&
> +	    key->type >= BTRFS_ROOT_ITEM_KEY &&
> +	    key->type <= BTRFS_ROOT_BACKREF_KEY)

Why returning all the range [BTRFS_ROOT_ITEM_KEY...BTRFS_ROOT_BACKREF_KEY]. It would be sufficient to return only

  +	    (key->type == BTRFS_ROOT_ITEM_KEY ||
  +	     key->type == BTRFS_ROOT_BACKREF_KEY))


> +		return 1;
> +
> +	return 0;
> +}
> +
>  static noinline int copy_to_sk(struct btrfs_path *path,
>  			       struct btrfs_key *key,
>  			       struct btrfs_ioctl_search_key *sk,
> @@ -2045,6 +2067,142 @@ static noinline int copy_to_sk(struct btrfs_path *path,
>  	return ret;
>  }
>  
> +/*
> + * Basically the same as copy_to_sk() but restricts the copied item
> + * within subvolume related one using key_in_sk_and_subvol().
> + * Also, the name of subvolume will be omitted from
> + * ROOT_BACKREF/ROOT_REF item.
> + */
> +static noinline int copy_subvol_item(struct btrfs_path *path,
> +			       struct btrfs_key *key,
> +			       struct btrfs_ioctl_search_key *sk,
> +			       size_t *buf_size,
> +			       char __user *ubuf,
> +			       unsigned long *sk_offset,
> +			       int *num_found)
> +{
> +	u64 found_transid;
> +	struct extent_buffer *leaf;
> +	struct btrfs_ioctl_search_header sh;
> +	struct btrfs_key test;
> +	unsigned long item_off;
> +	unsigned long item_len;
> +	int nritems;
> +	int i;
> +	int slot;
> +	int ret = 0;
> +
> +	leaf = path->nodes[0];
> +	slot = path->slots[0];
> +	nritems = btrfs_header_nritems(leaf);
> +
> +	if (btrfs_header_generation(leaf) > sk->max_transid) {
> +		i = nritems;
> +		goto advance_key;
> +	}
> +	found_transid = btrfs_header_generation(leaf);
> +
> +	for (i = slot; i < nritems; i++) {
> +		item_off = btrfs_item_ptr_offset(leaf, i);
> +		item_len = btrfs_item_size_nr(leaf, i);
> +
> +		btrfs_item_key_to_cpu(leaf, key, i);
> +		if (!key_in_sk_and_subvol(key, sk))
> +			continue;
> +
> +		/* will not copy the name of subvolume */
> +		if (key->type == BTRFS_ROOT_BACKREF_KEY ||
> +		    key->type == BTRFS_ROOT_REF_KEY)
> +			item_len = sizeof(struct btrfs_root_ref);
> +
> +		if (sizeof(sh) + item_len > *buf_size) {
> +			if (*num_found) {
> +				ret = 1;
> +				goto out;
> +			}
> +
> +			/*
> +			 * return one empty item back for v1, which does not
> +			 * handle -EOVERFLOW
> +			 */
It is still applicable ?
> +
> +			*buf_size = sizeof(sh) + item_len;
> +			item_len = 0;
> +			ret = -EOVERFLOW;> +		}
> +
> +		if (sizeof(sh) + item_len + *sk_offset > *buf_size) {
> +			ret = 1;
> +			goto out;
> +		}
> +
> +		sh.objectid = key->objectid;
> +		sh.offset = key->offset;
> +		sh.type = key->type;
> +		sh.len = item_len;
> +		sh.transid = found_transid;
> +
> +		/* copy search result header */
> +		if (copy_to_user(ubuf + *sk_offset, &sh, sizeof(sh))) {
> +			ret = -EFAULT;
> +			goto out;
> +		}
> +
> +		*sk_offset += sizeof(sh);
> +
> +		if (item_len) {
> +			char __user *up = ubuf + *sk_offset;
> +
> +			/* copy the item */
> +			if (read_extent_buffer_to_user(leaf, up,
> +						       item_off, item_len)) {
> +				ret = -EFAULT;
> +				goto out;
> +			}
> +
> +			*sk_offset += item_len;
> +		}
> +		(*num_found)++;
> +
> +		if (ret) /* -EOVERFLOW from above */
> +			goto out;
> +
> +		if (*num_found >= sk->nr_items) {
> +			ret = 1;
> +			goto out;
> +		}
> +	}
> +advance_key:
> +	ret = 0;
> +	test.objectid = sk->max_objectid;
> +	test.type = sk->max_type;
> +	test.offset = sk->max_offset;
> +	if (btrfs_comp_cpu_keys(key, &test) >= 0)
> +		ret = 1;
> +	else if (key->offset < (u64)-1)
> +		key->offset++;
> +	else if (key->type < (u8)-1) {
> +		key->offset = 0;
> +		key->type++;
> +	} else if (key->objectid < (u64)-1) {
> +		key->offset = 0;
> +		key->type = 0;
> +		key->objectid++;

It would be doable to check that type is in the range 
	[BTRFS_ROOT_ITEM_KEY...BTRFS_ROOT_BACKREF_KEY]

I.e. something like


 +	if (btrfs_comp_cpu_keys(key, &test) >= 0)
 +		ret = 1;
 +	else if (key->offset < (u64)-1)
 +		key->offset++;
 +	else if (key->type < BTRFS_ROOT_BACKREF_KEY) {
 +		key->offset = 0;
 +		key->type++;
 +	} else if (key->objectid < (u64)-1) {
 +		key->offset = 0;
 +		key->type = BTRFS_ROOT_ITEM_KEY;
 +		key->objectid++;



> +	} else
> +		ret = 1;
> +out:
> +	/*
> +	 *  0: all items from this leaf copied, continue with next
> +	 *  1: * more items can be copied, but unused buffer is too small
> +	 *     * all items were found
> +	 *     Either way, it will stops the loop which iterates to the next
> +	 *     leaf
> +	 *  -EOVERFLOW: item was to large for buffer
> +	 *  -EFAULT: could not copy extent buffer back to userspace
> +	 */
> +	return ret;
> +}
> +
>  static noinline int search_ioctl(struct inode *inode,
>  				 struct btrfs_ioctl_search_key *sk,
>  				 size_t *buf_size,
> @@ -2309,6 +2467,100 @@ static noinline int btrfs_ioctl_ino_lookup(struct file *file,
>  	return ret;
>  }
>  
> +static noinline int search_subvol(struct inode *inode,
> +				 struct btrfs_ioctl_search_key *sk,
> +				 size_t *buf_size,
> +				 char __user *ubuf)
> +{
> +	struct btrfs_fs_info *info = btrfs_sb(inode->i_sb);
> +	struct btrfs_root *root;
> +	struct btrfs_key key;
> +	struct btrfs_path *path;
> +	unsigned long sk_offset = 0;
> +	int num_found = 0;
> +	int ret;
> +
> +	path = btrfs_alloc_path();
> +	if (!path)
> +		return -ENOMEM;
> +
> +	/* search ROOT TREEE */
> +	key.objectid = BTRFS_ROOT_TREE_OBJECTID;
> +	key.type = BTRFS_ROOT_ITEM_KEY;
> +	key.offset = (u64)-1;
> +	root = btrfs_read_fs_root_no_name(info, &key);
> +	if (IS_ERR(root)) {
> +		btrfs_free_path(path);
> +		return -ENOENT;
> +	}
> +
> +	key.objectid = sk->min_objectid;
> +	key.type = sk->min_type;
> +	key.offset = sk->min_offset;
> +
> +	while (1) {
> +		ret = btrfs_search_forward(root, &key, path, sk->min_transid);
> +		if (ret != 0) {
> +			if (ret > 0)
> +				ret = 0;
> +			goto err;
> +		}
> +
> +		ret = copy_subvol_item(path, &key, sk, buf_size, ubuf,
> +				 &sk_offset, &num_found);
> +		btrfs_release_path(path);
> +		if (ret)
> +			break;
> +	}
> +
> +	if (ret > 0)
> +		ret = 0;
> +err:
> +	sk->nr_items = num_found;
> +	btrfs_free_path(path);
> +	return ret;
> +}
> +
> +/*
> + * Unprivileged ioctl for getting subvolume related item.
> + * The arguments are the same as btrfs_ioctl_tree_search()
> + * and can be used like tree search ioctl.
> + *
> + * Only returns ROOT_ITEM/ROOT_BACKREF/ROOT_REF key of subvolumes
> + * from root tree. Also, the name of subvolume will be omitted from
> + * ROOT_BACKREF/ROOT_REF item to prevent name leak.
> + */
> +static noinline int btrfs_ioctl_get_subvol_info(struct file *file,
> +					   void __user *argp)
> +{
> +	struct btrfs_ioctl_search_args __user *uargs;
> +	struct btrfs_ioctl_search_key sk;
> +	struct inode *inode;
> +	size_t buf_size;
> +	int ret;
> +
> +	uargs = (struct btrfs_ioctl_search_args __user *)argp;
> +
> +	if (copy_from_user(&sk, &uargs->key, sizeof(sk)))
> +		return -EFAULT;
> +
> +	buf_size = sizeof(uargs->buf);
> +
> +	inode = file_inode(file);
> +	ret = search_subvol(inode, &sk, &buf_size, uargs->buf);
> +
> +	/*
> +	 * In the original implementation an overflow is handled by returning a
> +	 * search header with a len of zero, so reset ret.
> +	 */
> +	if (ret == -EOVERFLOW)
> +		ret = 0;
> +
> +	if (ret == 0 && copy_to_user(&uargs->key, &sk, sizeof(sk)))
> +		ret = -EFAULT;
> +	return ret;
> +}
> +
>  static noinline int btrfs_ioctl_snap_destroy(struct file *file,
>  					     void __user *arg)
>  {
> @@ -5663,6 +5915,8 @@ 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..1e9361cf66d5 100644
> --- a/include/uapi/linux/btrfs.h
> +++ b/include/uapi/linux/btrfs.h
> @@ -843,5 +843,7 @@ 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 _IOWR(BTRFS_IOCTL_MAGIC, 60, \
> +					struct btrfs_ioctl_search_args)
>  
>  #endif /* _UAPI_LINUX_BTRFS_H */
>
Misono Tomohiro March 7, 2018, 12:40 a.m. UTC | #2
On 2018/03/07 5:29, Goffredo Baroncelli wrote:
> On 03/06/2018 09:30 AM, Misono, Tomohiro wrote:
>> Add new unprivileged ioctl (BTRFS_IOC_GET_SUBVOL_INFO) which searches
>> and returns only subvolume related item (ROOT_ITEM/ROOT_BACKREF/ROOT_REF)
>> from root tree. The arguments of this ioctl are the same as treesearch
>> ioctl and can be used like treesearch ioctl.
> 
> Is it a pro ? The treesearch ioctl is tightly coupled to the btrfs internal structure, this means that if we would change the btrfs internal structure, we have to update all the clients of this api. For the treesearch it is an acceptable compromise between flexibility and speed of developing. But for a more specialized API, I think that it would make sense to provide a less coupled api to the internal structure.

Thanks for the comments.

The reason I choose the same api is just to minimize the code change in btrfs-progs.
For tree search part, it works just switching the ioctl number from BTRFS_IOC_TREE_SEARCH
to BTRFS_IOC_GET_SUBVOL_INFO in list_subvol_search()[1].

[1] https://marc.info/?l=linux-btrfs&m=152032537911218&w=2

> 
> Below some comments
> 
> 
>>
>> Since treesearch ioctl requires root privilege, this ioctl is needed
>> to allow normal users to call "btrfs subvolume list/show" etc.
>>
>> Note that the subvolume name in ROOT_BACKREF/ROOT_REF will not be copied to
>> prevent potential name leak. The name can be obtained by calling
>> user version's ino_lookup ioctl (BTRFS_IOC_INO_LOOKUP_USER).
>>
>> Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
>> ---
>>  fs/btrfs/ioctl.c           | 254 +++++++++++++++++++++++++++++++++++++++++++++
>>  include/uapi/linux/btrfs.h |   2 +
>>  2 files changed, 256 insertions(+)
>>
>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>> index 111ee282b777..1dba309dce31 100644
>> --- a/fs/btrfs/ioctl.c
>> +++ b/fs/btrfs/ioctl.c
>> @@ -1921,6 +1921,28 @@ static noinline int key_in_sk(struct btrfs_key *key,
>>  	return 1;
>>  }
>>  
>> +/*
>> + * check if key is in sk and subvolume related range
>> + */
>> +static noinline int key_in_sk_and_subvol(struct btrfs_key *key,
>> +			      struct btrfs_ioctl_search_key *sk)
>> +{
>> +	int ret;
>> +
>> +	ret = key_in_sk(key, sk);
>> +	if (!ret)
>> +		return 0;
>> +
>> +	if ((key->objectid == BTRFS_FS_TREE_OBJECTID ||
>> +		(key->objectid >= BTRFS_FIRST_FREE_OBJECTID &&
>> +		 key->objectid <= BTRFS_LAST_FREE_OBJECTID)) &&
>> +	    key->type >= BTRFS_ROOT_ITEM_KEY &&
>> +	    key->type <= BTRFS_ROOT_BACKREF_KEY)
> 
> Why returning all the range [BTRFS_ROOT_ITEM_KEY...BTRFS_ROOT_BACKREF_KEY]. It would be sufficient to return only
> 
>   +	    (key->type == BTRFS_ROOT_ITEM_KEY ||
>   +	     key->type == BTRFS_ROOT_BACKREF_KEY))

Sorry, it is a mistake, I mean "key->type <= BTRFS_ROOTREF_KEY".
Although btrfs-progs only uses BTRFS_ROOT_BACKREF_KEY, I notice libbtrfs 
uses BTRFS_ROOT_REF_KEY instead. So, I think it is better to return both
ROOT_BACKREF_KEY and ROOT_REF_KEY. I will fix this in v2.

> 
> 
>> +		return 1;
>> +
>> +	return 0;
>> +}
>> +
>>  static noinline int copy_to_sk(struct btrfs_path *path,
>>  			       struct btrfs_key *key,
>>  			       struct btrfs_ioctl_search_key *sk,
>> @@ -2045,6 +2067,142 @@ static noinline int copy_to_sk(struct btrfs_path *path,
>>  	return ret;
>>  }
>>  
>> +/*
>> + * Basically the same as copy_to_sk() but restricts the copied item
>> + * within subvolume related one using key_in_sk_and_subvol().
>> + * Also, the name of subvolume will be omitted from
>> + * ROOT_BACKREF/ROOT_REF item.
>> + */
>> +static noinline int copy_subvol_item(struct btrfs_path *path,
>> +			       struct btrfs_key *key,
>> +			       struct btrfs_ioctl_search_key *sk,
>> +			       size_t *buf_size,
>> +			       char __user *ubuf,
>> +			       unsigned long *sk_offset,
>> +			       int *num_found)
>> +{
>> +	u64 found_transid;
>> +	struct extent_buffer *leaf;
>> +	struct btrfs_ioctl_search_header sh;
>> +	struct btrfs_key test;
>> +	unsigned long item_off;
>> +	unsigned long item_len;
>> +	int nritems;
>> +	int i;
>> +	int slot;
>> +	int ret = 0;
>> +
>> +	leaf = path->nodes[0];
>> +	slot = path->slots[0];
>> +	nritems = btrfs_header_nritems(leaf);
>> +
>> +	if (btrfs_header_generation(leaf) > sk->max_transid) {
>> +		i = nritems;
>> +		goto advance_key;
>> +	}
>> +	found_transid = btrfs_header_generation(leaf);
>> +
>> +	for (i = slot; i < nritems; i++) {
>> +		item_off = btrfs_item_ptr_offset(leaf, i);
>> +		item_len = btrfs_item_size_nr(leaf, i);
>> +
>> +		btrfs_item_key_to_cpu(leaf, key, i);
>> +		if (!key_in_sk_and_subvol(key, sk))
>> +			continue;
>> +
>> +		/* will not copy the name of subvolume */
>> +		if (key->type == BTRFS_ROOT_BACKREF_KEY ||
>> +		    key->type == BTRFS_ROOT_REF_KEY)
>> +			item_len = sizeof(struct btrfs_root_ref);
>> +
>> +		if (sizeof(sh) + item_len > *buf_size) {
>> +			if (*num_found) {
>> +				ret = 1;
>> +				goto out;
>> +			}
>> +
>> +			/*
>> +			 * return one empty item back for v1, which does not
>> +			 * handle -EOVERFLOW
>> +			 */
> It is still applicable ?
In order to just replace TREE_SEARCH (v1) in user space, I think it still needs
the same EOVERFLOW handling like TREE_SEARCH does (in copy_to_sk() and btrfs_ioctl_tree_search()).

>> +
>> +			*buf_size = sizeof(sh) + item_len;
>> +			item_len = 0;
>> +			ret = -EOVERFLOW;> +		}
>> +
>> +		if (sizeof(sh) + item_len + *sk_offset > *buf_size) {
>> +			ret = 1;
>> +			goto out;
>> +		}
>> +
>> +		sh.objectid = key->objectid;
>> +		sh.offset = key->offset;
>> +		sh.type = key->type;
>> +		sh.len = item_len;
>> +		sh.transid = found_transid;
>> +
>> +		/* copy search result header */
>> +		if (copy_to_user(ubuf + *sk_offset, &sh, sizeof(sh))) {
>> +			ret = -EFAULT;
>> +			goto out;
>> +		}
>> +
>> +		*sk_offset += sizeof(sh);
>> +
>> +		if (item_len) {
>> +			char __user *up = ubuf + *sk_offset;
>> +
>> +			/* copy the item */
>> +			if (read_extent_buffer_to_user(leaf, up,
>> +						       item_off, item_len)) {
>> +				ret = -EFAULT;
>> +				goto out;
>> +			}
>> +
>> +			*sk_offset += item_len;
>> +		}
>> +		(*num_found)++;
>> +
>> +		if (ret) /* -EOVERFLOW from above */
>> +			goto out;
>> +
>> +		if (*num_found >= sk->nr_items) {
>> +			ret = 1;
>> +			goto out;
>> +		}
>> +	}
>> +advance_key:
>> +	ret = 0;
>> +	test.objectid = sk->max_objectid;
>> +	test.type = sk->max_type;
>> +	test.offset = sk->max_offset;
>> +	if (btrfs_comp_cpu_keys(key, &test) >= 0)
>> +		ret = 1;
>> +	else if (key->offset < (u64)-1)
>> +		key->offset++;
>> +	else if (key->type < (u8)-1) {
>> +		key->offset = 0;
>> +		key->type++;
>> +	} else if (key->objectid < (u64)-1) {
>> +		key->offset = 0;
>> +		key->type = 0;
>> +		key->objectid++;
> 
> It would be doable to check that type is in the range 
> 	[BTRFS_ROOT_ITEM_KEY...BTRFS_ROOT_BACKREF_KEY]
> 
> I.e. something like
> 
> 
>  +	if (btrfs_comp_cpu_keys(key, &test) >= 0)
>  +		ret = 1;
>  +	else if (key->offset < (u64)-1)
>  +		key->offset++;
>  +	else if (key->type < BTRFS_ROOT_BACKREF_KEY) {
>  +		key->offset = 0;
>  +		key->type++;
>  +	} else if (key->objectid < (u64)-1) {
>  +		key->offset = 0;
>  +		key->type = BTRFS_ROOT_ITEM_KEY;
>  +		key->objectid++;

Thanks, I will fix this in v2.

> 
>> +	} else
>> +		ret = 1;
>> +out:
>> +	/*
>> +	 *  0: all items from this leaf copied, continue with next
>> +	 *  1: * more items can be copied, but unused buffer is too small
>> +	 *     * all items were found
>> +	 *     Either way, it will stops the loop which iterates to the next
>> +	 *     leaf
>> +	 *  -EOVERFLOW: item was to large for buffer
>> +	 *  -EFAULT: could not copy extent buffer back to userspace
>> +	 */
>> +	return ret;
>> +}
>> +
>>  static noinline int search_ioctl(struct inode *inode,
>>  				 struct btrfs_ioctl_search_key *sk,
>>  				 size_t *buf_size,
>> @@ -2309,6 +2467,100 @@ static noinline int btrfs_ioctl_ino_lookup(struct file *file,
>>  	return ret;
>>  }
>>  
>> +static noinline int search_subvol(struct inode *inode,
>> +				 struct btrfs_ioctl_search_key *sk,
>> +				 size_t *buf_size,
>> +				 char __user *ubuf)
>> +{
>> +	struct btrfs_fs_info *info = btrfs_sb(inode->i_sb);
>> +	struct btrfs_root *root;
>> +	struct btrfs_key key;
>> +	struct btrfs_path *path;
>> +	unsigned long sk_offset = 0;
>> +	int num_found = 0;
>> +	int ret;
>> +
>> +	path = btrfs_alloc_path();
>> +	if (!path)
>> +		return -ENOMEM;
>> +
>> +	/* search ROOT TREEE */
>> +	key.objectid = BTRFS_ROOT_TREE_OBJECTID;
>> +	key.type = BTRFS_ROOT_ITEM_KEY;
>> +	key.offset = (u64)-1;
>> +	root = btrfs_read_fs_root_no_name(info, &key);
>> +	if (IS_ERR(root)) {
>> +		btrfs_free_path(path);
>> +		return -ENOENT;
>> +	}
>> +
>> +	key.objectid = sk->min_objectid;
>> +	key.type = sk->min_type;
>> +	key.offset = sk->min_offset;
>> +
>> +	while (1) {
>> +		ret = btrfs_search_forward(root, &key, path, sk->min_transid);
>> +		if (ret != 0) {
>> +			if (ret > 0)
>> +				ret = 0;
>> +			goto err;
>> +		}
>> +
>> +		ret = copy_subvol_item(path, &key, sk, buf_size, ubuf,
>> +				 &sk_offset, &num_found);
>> +		btrfs_release_path(path);
>> +		if (ret)
>> +			break;
>> +	}
>> +
>> +	if (ret > 0)
>> +		ret = 0;
>> +err:
>> +	sk->nr_items = num_found;
>> +	btrfs_free_path(path);
>> +	return ret;
>> +}
>> +
>> +/*
>> + * Unprivileged ioctl for getting subvolume related item.
>> + * The arguments are the same as btrfs_ioctl_tree_search()
>> + * and can be used like tree search ioctl.
>> + *
>> + * Only returns ROOT_ITEM/ROOT_BACKREF/ROOT_REF key of subvolumes
>> + * from root tree. Also, the name of subvolume will be omitted from
>> + * ROOT_BACKREF/ROOT_REF item to prevent name leak.
>> + */
>> +static noinline int btrfs_ioctl_get_subvol_info(struct file *file,
>> +					   void __user *argp)
>> +{
>> +	struct btrfs_ioctl_search_args __user *uargs;
>> +	struct btrfs_ioctl_search_key sk;
>> +	struct inode *inode;
>> +	size_t buf_size;
>> +	int ret;
>> +
>> +	uargs = (struct btrfs_ioctl_search_args __user *)argp;
>> +
>> +	if (copy_from_user(&sk, &uargs->key, sizeof(sk)))
>> +		return -EFAULT;
>> +
>> +	buf_size = sizeof(uargs->buf);
>> +
>> +	inode = file_inode(file);
>> +	ret = search_subvol(inode, &sk, &buf_size, uargs->buf);
>> +
>> +	/*
>> +	 * In the original implementation an overflow is handled by returning a
>> +	 * search header with a len of zero, so reset ret.
>> +	 */
>> +	if (ret == -EOVERFLOW)
>> +		ret = 0;
>> +
>> +	if (ret == 0 && copy_to_user(&uargs->key, &sk, sizeof(sk)))
>> +		ret = -EFAULT;
>> +	return ret;
>> +}
>> +
>>  static noinline int btrfs_ioctl_snap_destroy(struct file *file,
>>  					     void __user *arg)
>>  {
>> @@ -5663,6 +5915,8 @@ 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..1e9361cf66d5 100644
>> --- a/include/uapi/linux/btrfs.h
>> +++ b/include/uapi/linux/btrfs.h
>> @@ -843,5 +843,7 @@ 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 _IOWR(BTRFS_IOCTL_MAGIC, 60, \
>> +					struct btrfs_ioctl_search_args)
>>  
>>  #endif /* _UAPI_LINUX_BTRFS_H */
>>
> 
> 

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David Sterba March 7, 2018, 4:36 p.m. UTC | #3
On Wed, Mar 07, 2018 at 09:40:18AM +0900, Misono, Tomohiro wrote:
> On 2018/03/07 5:29, Goffredo Baroncelli wrote:
> > On 03/06/2018 09:30 AM, Misono, Tomohiro wrote:
> >> Add new unprivileged ioctl (BTRFS_IOC_GET_SUBVOL_INFO) which searches
> >> and returns only subvolume related item (ROOT_ITEM/ROOT_BACKREF/ROOT_REF)
> >> from root tree. The arguments of this ioctl are the same as treesearch
> >> ioctl and can be used like treesearch ioctl.
> > 
> > Is it a pro ? The treesearch ioctl is tightly coupled to the btrfs internal structure, this means that if we would change the btrfs internal structure, we have to update all the clients of this api. For the treesearch it is an acceptable compromise between flexibility and speed of developing. But for a more specialized API, I think that it would make sense to provide a less coupled api to the internal structure.
> 
> Thanks for the comments.
> 
> The reason I choose the same api is just to minimize the code change in btrfs-progs.

That's not IMO a good reason. We can cahnge the code in btrfs-progs and
that's not going to be the only user of the ioctl so the interfact (ie.
the structures) should be adapted for the needs of the ioctl.
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Goffredo Baroncelli March 7, 2018, 7 p.m. UTC | #4
On 03/07/2018 01:40 AM, Misono, Tomohiro wrote:
> On 2018/03/07 5:29, Goffredo Baroncelli wrote:
>> On 03/06/2018 09:30 AM, Misono, Tomohiro wrote:
>>> Add new unprivileged ioctl (BTRFS_IOC_GET_SUBVOL_INFO) which searches
>>> and returns only subvolume related item (ROOT_ITEM/ROOT_BACKREF/ROOT_REF)
>>> from root tree. The arguments of this ioctl are the same as treesearch
>>> ioctl and can be used like treesearch ioctl.
>>
>> Is it a pro ? The treesearch ioctl is tightly coupled to the btrfs internal structure, this means that if we would change the btrfs internal structure, we have to update all the clients of this api. For the treesearch it is an acceptable compromise between flexibility and speed of developing. But for a more specialized API, I think that it would make sense to provide a less coupled api to the internal structure.
> 
> Thanks for the comments.
> 
> The reason I choose the same api is just to minimize the code change in btrfs-progs.
> For tree search part, it works just switching the ioctl number from BTRFS_IOC_TREE_SEARCH
> to BTRFS_IOC_GET_SUBVOL_INFO in list_subvol_search()[1].
> 
> [1] https://marc.info/?l=linux-btrfs&m=152032537911218&w=2

I suggest to avoid this approach. An API is forever; we already have a "root-only" one which is quite unfriendly and error prone; I think that we should put all the energies to make a better one. 

I think that the major weaknesses of this api are:
- it exports the the data in "le" format  (see struct btrfs_root_item as example); 
- it requires the user to increase the key for the next ioctl call. This could be doable in the kernel space before returning
- this ioctl exports both the ROOT_BACKREF and ROOT_ITEM info. Why not make two separate (simplers) ioctl(s) ?

>>
>> Below some comments
[...]

>>> +	if ((key->objectid == BTRFS_FS_TREE_OBJECTID ||
>>> +		(key->objectid >= BTRFS_FIRST_FREE_OBJECTID &&
>>> +		 key->objectid <= BTRFS_LAST_FREE_OBJECTID)) &&
>>> +	    key->type >= BTRFS_ROOT_ITEM_KEY &&
>>> +	    key->type <= BTRFS_ROOT_BACKREF_KEY)
>>
>> Why returning all the range [BTRFS_ROOT_ITEM_KEY...BTRFS_ROOT_BACKREF_KEY]. It would be sufficient to return only
>>
>>   +	    (key->type == BTRFS_ROOT_ITEM_KEY ||
>>   +	     key->type == BTRFS_ROOT_BACKREF_KEY))
> 
> Sorry, it is a mistake, I mean "key->type <= BTRFS_ROOTREF_KEY".
> Although btrfs-progs only uses BTRFS_ROOT_BACKREF_KEY, I notice libbtrfs 
> uses BTRFS_ROOT_REF_KEY instead. So, I think it is better to return both
> ROOT_BACKREF_KEY and ROOT_REF_KEY. I will fix this in v2.
> 

I was referring to the '>=' and '<=' instead of '=='. If another type is added in the middle, it would be returned. I find it a bit error prone.

BR
G.Baroncelli
Nikolay Borisov March 8, 2018, 8:29 a.m. UTC | #5
On  6.03.2018 10:30, Misono, Tomohiro wrote:
> Add new unprivileged ioctl (BTRFS_IOC_GET_SUBVOL_INFO) which searches
> and returns only subvolume related item (ROOT_ITEM/ROOT_BACKREF/ROOT_REF)
> from root tree. The arguments of this ioctl are the same as treesearch
> ioctl and can be used like treesearch ioctl.
> 
> Since treesearch ioctl requires root privilege, this ioctl is needed
> to allow normal users to call "btrfs subvolume list/show" etc.
> 
> Note that the subvolume name in ROOT_BACKREF/ROOT_REF will not be copied to
> prevent potential name leak. The name can be obtained by calling
> user version's ino_lookup ioctl (BTRFS_IOC_INO_LOOKUP_USER).
> 
> Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
> ---
>  fs/btrfs/ioctl.c           | 254 +++++++++++++++++++++++++++++++++++++++++++++
>  include/uapi/linux/btrfs.h |   2 +
>  2 files changed, 256 insertions(+)
> 
> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
> index 111ee282b777..1dba309dce31 100644
> --- a/fs/btrfs/ioctl.c
> +++ b/fs/btrfs/ioctl.c
> @@ -1921,6 +1921,28 @@ static noinline int key_in_sk(struct btrfs_key *key,
>  	return 1;
>  }
>  
> +/*
> + * check if key is in sk and subvolume related range
> + */
> +static noinline int key_in_sk_and_subvol(struct btrfs_key *key,
> +			      struct btrfs_ioctl_search_key *sk)
> +{
> +	int ret;
> +
> +	ret = key_in_sk(key, sk);
> +	if (!ret)
> +		return 0;
> +
> +	if ((key->objectid == BTRFS_FS_TREE_OBJECTID ||
> +		(key->objectid >= BTRFS_FIRST_FREE_OBJECTID &&
> +		 key->objectid <= BTRFS_LAST_FREE_OBJECTID)) &&

Why do you need the FIRST_FREE/LAST_FREE object id checks? The range
described by those are ordinary files. Since you are only interested in
subvolume data then you should omit those, no?

> +	    key->type >= BTRFS_ROOT_ITEM_KEY &&
> +	    key->type <= BTRFS_ROOT_BACKREF_KEY)
I think this check should really be:

if (key->objectid == BTRFS_FS_TREE_OBJECTID || key->objectid ==
BTRFS_ROOT_ITEM_KEY || key->type == BTRFS_ROOT_BACKREF_KEY

> +		return 1;
> +
> +	return 0;
> +}
> +
>  static noinline int copy_to_sk(struct btrfs_path *path,
>  			       struct btrfs_key *key,
>  			       struct btrfs_ioctl_search_key *sk,
> @@ -2045,6 +2067,142 @@ static noinline int copy_to_sk(struct btrfs_path *path,
>  	return ret;
>  }
>  
> +/*
> + * Basically the same as copy_to_sk() but restricts the copied item
> + * within subvolume related one using key_in_sk_and_subvol().
> + * Also, the name of subvolume will be omitted from
> + * ROOT_BACKREF/ROOT_REF item.
> + */
> +static noinline int copy_subvol_item(struct btrfs_path *path,
> +			       struct btrfs_key *key,
> +			       struct btrfs_ioctl_search_key *sk,
> +			       size_t *buf_size,
> +			       char __user *ubuf,
> +			       unsigned long *sk_offset,
> +			       int *num_found)
> +{
> +	u64 found_transid;
> +	struct extent_buffer *leaf;
> +	struct btrfs_ioctl_search_header sh;
> +	struct btrfs_key test;
> +	unsigned long item_off;
> +	unsigned long item_len;
> +	int nritems;
> +	int i;
> +	int slot;
> +	int ret = 0;
> +
> +	leaf = path->nodes[0];
> +	slot = path->slots[0];
> +	nritems = btrfs_header_nritems(leaf);
> +
> +	if (btrfs_header_generation(leaf) > sk->max_transid) {
> +		i = nritems;
> +		goto advance_key;

I don't see why you need a goto label at all. Just put the necessary
code inside the if and return directly.

> +	}
> +	found_transid = btrfs_header_generation(leaf);
> +
> +	for (i = slot; i < nritems; i++) {
> +		item_off = btrfs_item_ptr_offset(leaf, i);
> +		item_len = btrfs_item_size_nr(leaf, i);
> +
> +		btrfs_item_key_to_cpu(leaf, key, i);
> +		if (!key_in_sk_and_subvol(key, sk))
> +			continue;
> +
> +		/* will not copy the name of subvolume */
> +		if (key->type == BTRFS_ROOT_BACKREF_KEY ||
> +		    key->type == BTRFS_ROOT_REF_KEY)
> +			item_len = sizeof(struct btrfs_root_ref);
> +
> +		if (sizeof(sh) + item_len > *buf_size) {
> +			if (*num_found) {
> +				ret = 1;
> +				goto out;
 This can be a simple return 1;


> +			}
> +
> +			/*
> +			 * return one empty item back for v1, which does not
> +			 * handle -EOVERFLOW
> +			 */
> +
> +			*buf_size = sizeof(sh) + item_len;
> +			item_len = 0;
> +			ret = -EOVERFLOW;
> +		}
> +
> +		if (sizeof(sh) + item_len + *sk_offset > *buf_size) {
> +			ret = 1;
> +			goto out;
ditto
> +		}
> +
> +		sh.objectid = key->objectid;
> +		sh.offset = key->offset;
> +		sh.type = key->type;
> +		sh.len = item_len;
> +		sh.transid = found_transid;
> +
> +		/* copy search result header */
> +		if (copy_to_user(ubuf + *sk_offset, &sh, sizeof(sh))) {
> +			ret = -EFAULT;
> +			goto out;
ditto
> +		}
> +
> +		*sk_offset += sizeof(sh);
> +
> +		if (item_len) {
> +			char __user *up = ubuf + *sk_offset;
> +
> +			/* copy the item */
> +			if (read_extent_buffer_to_user(leaf, up,
> +						       item_off, item_len)) {
> +				ret = -EFAULT;
> +				goto out;
ditto
> +			}
> +
> +			*sk_offset += item_len;
> +		}
> +		(*num_found)++;
> +
> +		if (ret) /* -EOVERFLOW from above */
> +			goto out;
return ret
> +
> +		if (*num_found >= sk->nr_items) {
> +			ret = 1;
> +			goto out;
return 1
> +		}
> +	}
> +advance_key:
> +	ret = 0;
> +	test.objectid = sk->max_objectid;
> +	test.type = sk->max_type;
> +	test.offset = sk->max_offset;
> +	if (btrfs_comp_cpu_keys(key, &test) >= 0)
> +		ret = 1;
> +	else if (key->offset < (u64)-1)
> +		key->offset++;
> +	else if (key->type < (u8)-1) {
> +		key->offset = 0;
> +		key->type++;
> +	} else if (key->objectid < (u64)-1) {
> +		key->offset = 0;
> +		key->type = 0;
> +		key->objectid++;
> +	} else
> +		ret = 1;
> +out:

Given that you are not doing any unwinding of locks or some such I don't
see any reason for the label at all.

> +	/*
> +	 *  0: all items from this leaf copied, continue with next
> +	 *  1: * more items can be copied, but unused buffer is too small
> +	 *     * all items were found
> +	 *     Either way, it will stops the loop which iterates to the next
> +	 *     leaf
> +	 *  -EOVERFLOW: item was to large for buffer
> +	 *  -EFAULT: could not copy extent buffer back to userspace
> +	 */
Put the description of the return value above the function definition
> +	return ret;
> +}
> +
>  static noinline int search_ioctl(struct inode *inode,
>  				 struct btrfs_ioctl_search_key *sk,
>  				 size_t *buf_size,
> @@ -2309,6 +2467,100 @@ static noinline int btrfs_ioctl_ino_lookup(struct file *file,
>  	return ret;
>  }
>  
> +static noinline int search_subvol(struct inode *inode,
> +				 struct btrfs_ioctl_search_key *sk,
> +				 size_t *buf_size,
> +				 char __user *ubuf)
> +{
> +	struct btrfs_fs_info *info = btrfs_sb(inode->i_sb);
> +	struct btrfs_root *root;
> +	struct btrfs_key key;
> +	struct btrfs_path *path;
> +	unsigned long sk_offset = 0;
> +	int num_found = 0;
> +	int ret;
> +
> +	path = btrfs_alloc_path();
> +	if (!path)
> +		return -ENOMEM;
> +
> +	/* search ROOT TREEE */
> +	key.objectid = BTRFS_ROOT_TREE_OBJECTID;
> +	key.type = BTRFS_ROOT_ITEM_KEY;
> +	key.offset = (u64)-1;
> +	root = btrfs_read_fs_root_no_name(info, &key);
> +	if (IS_ERR(root)) {
> +		btrfs_free_path(path);
> +		return -ENOENT;
> +	}

So why do you have to do this, when you can just do :
struct btrfs_root *root = fs_info->tree_root;

Looking at the wider codebase, the root tree is referenced directly
almost all the time. btrfs_read_fs_root_no_name is generally used when
you have the objectid of a particular subvol root item and you want to
get that one. But this is not the case here.

> +
> +	key.objectid = sk->min_objectid;
> +	key.type = sk->min_type;
> +	key.offset = sk->min_offset;
> +
> +	while (1) {
> +		ret = btrfs_search_forward(root, &key, path, sk->min_transid);
> +		if (ret != 0) {
> +			if (ret > 0)
> +				ret = 0;
> +			goto err;
> +		}
> +
> +		ret = copy_subvol_item(path, &key, sk, buf_size, ubuf,
> +				 &sk_offset, &num_found);
> +		btrfs_release_path(path);
> +		if (ret)
> +			break;
> +	}
> +
> +	if (ret > 0)
> +		ret = 0;
> +err:
> +	sk->nr_items = num_found;
> +	btrfs_free_path(path);
> +	return ret;
> +}
> +
> +/*
> + * Unprivileged ioctl for getting subvolume related item.
> + * The arguments are the same as btrfs_ioctl_tree_search()
> + * and can be used like tree search ioctl.
> + *
> + * Only returns ROOT_ITEM/ROOT_BACKREF/ROOT_REF key of subvolumes
> + * from root tree. Also, the name of subvolume will be omitted from
> + * ROOT_BACKREF/ROOT_REF item to prevent name leak.
> + */
> +static noinline int btrfs_ioctl_get_subvol_info(struct file *file,
> +					   void __user *argp)
> +{
> +	struct btrfs_ioctl_search_args __user *uargs;
> +	struct btrfs_ioctl_search_key sk;
> +	struct inode *inode;
> +	size_t buf_size;
> +	int ret;
> +
> +	uargs = (struct btrfs_ioctl_search_args __user *)argp;
> +
> +	if (copy_from_user(&sk, &uargs->key, sizeof(sk)))
> +		return -EFAULT;
> +
> +	buf_size = sizeof(uargs->buf);
> +
> +	inode = file_inode(file);
> +	ret = search_subvol(inode, &sk, &buf_size, uargs->buf);
> +
> +	/*
> +	 * In the original implementation an overflow is handled by returning a
> +	 * search header with a len of zero, so reset ret.
> +	 */
> +	if (ret == -EOVERFLOW)
> +		ret = 0;
> +
> +	if (ret == 0 && copy_to_user(&uargs->key, &sk, sizeof(sk)))
> +		ret = -EFAULT;
> +	return ret;
> +}
> +
>  static noinline int btrfs_ioctl_snap_destroy(struct file *file,
>  					     void __user *arg)
>  {
> @@ -5663,6 +5915,8 @@ 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..1e9361cf66d5 100644
> --- a/include/uapi/linux/btrfs.h
> +++ b/include/uapi/linux/btrfs.h
> @@ -843,5 +843,7 @@ 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 _IOWR(BTRFS_IOCTL_MAGIC, 60, \
> +					struct btrfs_ioctl_search_args)
>  
>  #endif /* _UAPI_LINUX_BTRFS_H */
> 
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Misono Tomohiro March 9, 2018, 1:10 a.m. UTC | #6
On 2018/03/08 4:00, Goffredo Baroncelli wrote:
> On 03/07/2018 01:40 AM, Misono, Tomohiro wrote:
>> On 2018/03/07 5:29, Goffredo Baroncelli wrote:
>>> On 03/06/2018 09:30 AM, Misono, Tomohiro wrote:
>>>> Add new unprivileged ioctl (BTRFS_IOC_GET_SUBVOL_INFO) which searches
>>>> and returns only subvolume related item (ROOT_ITEM/ROOT_BACKREF/ROOT_REF)
>>>> from root tree. The arguments of this ioctl are the same as treesearch
>>>> ioctl and can be used like treesearch ioctl.
>>>
>>> Is it a pro ? The treesearch ioctl is tightly coupled to the btrfs internal structure, this means that if we would change the btrfs internal structure, we have to update all the clients of this api. For the treesearch it is an acceptable compromise between flexibility and speed of developing. But for a more specialized API, I think that it would make sense to provide a less coupled api to the internal structure.
>>
>> Thanks for the comments.
>>
>> The reason I choose the same api is just to minimize the code change in btrfs-progs.
>> For tree search part, it works just switching the ioctl number from BTRFS_IOC_TREE_SEARCH
>> to BTRFS_IOC_GET_SUBVOL_INFO in list_subvol_search()[1].
>>
>> [1] https://marc.info/?l=linux-btrfs&m=152032537911218&w=2
> 
> I suggest to avoid this approach. An API is forever; we already have a "root-only" one which is quite unfriendly and error prone; I think that we should put all the energies to make a better one. 
> 
> I think that the major weaknesses of this api are:
> - it exports the the data in "le" format  (see struct btrfs_root_item as example); 
> - it requires the user to increase the key for the next ioctl call. This could be doable in the kernel space before returning
> - this ioctl exports both the ROOT_BACKREF and ROOT_ITEM info. Why not make two separate (simplers) ioctl(s) ?

I agree with you and will split this ioctl into two pats (one is for getting ROOT_ITEM and the other for ROOT_REF/BACKREF)
and make them to have user friendly apis.

> 
>>>
>>> Below some comments
> [...]
> 
>>>> +	if ((key->objectid == BTRFS_FS_TREE_OBJECTID ||
>>>> +		(key->objectid >= BTRFS_FIRST_FREE_OBJECTID &&
>>>> +		 key->objectid <= BTRFS_LAST_FREE_OBJECTID)) &&
>>>> +	    key->type >= BTRFS_ROOT_ITEM_KEY &&
>>>> +	    key->type <= BTRFS_ROOT_BACKREF_KEY)
>>>
>>> Why returning all the range [BTRFS_ROOT_ITEM_KEY...BTRFS_ROOT_BACKREF_KEY]. It would be sufficient to return only
>>>
>>>   +	    (key->type == BTRFS_ROOT_ITEM_KEY ||
>>>   +	     key->type == BTRFS_ROOT_BACKREF_KEY))
>>
>> Sorry, it is a mistake, I mean "key->type <= BTRFS_ROOTREF_KEY".
>> Although btrfs-progs only uses BTRFS_ROOT_BACKREF_KEY, I notice libbtrfs 
>> uses BTRFS_ROOT_REF_KEY instead. So, I think it is better to return both
>> ROOT_BACKREF_KEY and ROOT_REF_KEY. I will fix this in v2.
>>
> 
> I was referring to the '>=' and '<=' instead of '=='. If another type is added in the middle, it would be returned. I find it a bit error prone.

ok, I will change this. thanks.
Tomohiro Misono

> 
> BR
> G.Baroncelli
> 

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Misono Tomohiro March 9, 2018, 1:16 a.m. UTC | #7
On 2018/03/08 17:29, Nikolay Borisov wrote:
> 
> 
> On  6.03.2018 10:30, Misono, Tomohiro wrote:
>> Add new unprivileged ioctl (BTRFS_IOC_GET_SUBVOL_INFO) which searches
>> and returns only subvolume related item (ROOT_ITEM/ROOT_BACKREF/ROOT_REF)
>> from root tree. The arguments of this ioctl are the same as treesearch
>> ioctl and can be used like treesearch ioctl.
>>
>> Since treesearch ioctl requires root privilege, this ioctl is needed
>> to allow normal users to call "btrfs subvolume list/show" etc.
>>
>> Note that the subvolume name in ROOT_BACKREF/ROOT_REF will not be copied to
>> prevent potential name leak. The name can be obtained by calling
>> user version's ino_lookup ioctl (BTRFS_IOC_INO_LOOKUP_USER).
>>
>> Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
>> ---
>>  fs/btrfs/ioctl.c           | 254 +++++++++++++++++++++++++++++++++++++++++++++
>>  include/uapi/linux/btrfs.h |   2 +
>>  2 files changed, 256 insertions(+)
>>
>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
>> index 111ee282b777..1dba309dce31 100644
>> --- a/fs/btrfs/ioctl.c
>> +++ b/fs/btrfs/ioctl.c
>> @@ -1921,6 +1921,28 @@ static noinline int key_in_sk(struct btrfs_key *key,
>>  	return 1;
>>  }
>>  
>> +/*
>> + * check if key is in sk and subvolume related range
>> + */
>> +static noinline int key_in_sk_and_subvol(struct btrfs_key *key,
>> +			      struct btrfs_ioctl_search_key *sk)
>> +{
>> +	int ret;
>> +
>> +	ret = key_in_sk(key, sk);
>> +	if (!ret)
>> +		return 0;
>> +
>> +	if ((key->objectid == BTRFS_FS_TREE_OBJECTID ||
>> +		(key->objectid >= BTRFS_FIRST_FREE_OBJECTID &&
>> +		 key->objectid <= BTRFS_LAST_FREE_OBJECTID)) &&
> 
> Why do you need the FIRST_FREE/LAST_FREE object id checks? The range
> described by those are ordinary files. Since you are only interested in
> subvolume data then you should omit those, no?

There are ROOT_ITEM for other trees (EXTETN_TREE, DEV_TREE etc.) and they should be skipped.

> 
>> +	    key->type >= BTRFS_ROOT_ITEM_KEY &&
>> +	    key->type <= BTRFS_ROOT_BACKREF_KEY)
> I think this check should really be:
> 
> if (key->objectid == BTRFS_FS_TREE_OBJECTID || key->objectid ==
> BTRFS_ROOT_ITEM_KEY || key->type == BTRFS_ROOT_BACKREF_KEY
>>> +		return 1;
>> +
>> +	return 0;
>> +}
>> +
>>  static noinline int copy_to_sk(struct btrfs_path *path,
>>  			       struct btrfs_key *key,
>>  			       struct btrfs_ioctl_search_key *sk,
>> @@ -2045,6 +2067,142 @@ static noinline int copy_to_sk(struct btrfs_path *path,
>>  	return ret;
>>  }
>>  
>> +/*
>> + * Basically the same as copy_to_sk() but restricts the copied item
>> + * within subvolume related one using key_in_sk_and_subvol().
>> + * Also, the name of subvolume will be omitted from
>> + * ROOT_BACKREF/ROOT_REF item.
>> + */
>> +static noinline int copy_subvol_item(struct btrfs_path *path,
>> +			       struct btrfs_key *key,
>> +			       struct btrfs_ioctl_search_key *sk,
>> +			       size_t *buf_size,
>> +			       char __user *ubuf,
>> +			       unsigned long *sk_offset,
>> +			       int *num_found)
>> +{
>> +	u64 found_transid;
>> +	struct extent_buffer *leaf;
>> +	struct btrfs_ioctl_search_header sh;
>> +	struct btrfs_key test;
>> +	unsigned long item_off;
>> +	unsigned long item_len;
>> +	int nritems;
>> +	int i;
>> +	int slot;
>> +	int ret = 0;
>> +
>> +	leaf = path->nodes[0];
>> +	slot = path->slots[0];
>> +	nritems = btrfs_header_nritems(leaf);
>> +
>> +	if (btrfs_header_generation(leaf) > sk->max_transid) {
>> +		i = nritems;
>> +		goto advance_key;
> 
> I don't see why you need a goto label at all. Just put the necessary
> code inside the if and return directly.

Most of this code is just copied from copy_to_sk().
I will rewrite code in more appropriate way in future version.

> 
>> +	}
>> +	found_transid = btrfs_header_generation(leaf);
>> +
>> +	for (i = slot; i < nritems; i++) {
>> +		item_off = btrfs_item_ptr_offset(leaf, i);
>> +		item_len = btrfs_item_size_nr(leaf, i);
>> +
>> +		btrfs_item_key_to_cpu(leaf, key, i);
>> +		if (!key_in_sk_and_subvol(key, sk))
>> +			continue;
>> +
>> +		/* will not copy the name of subvolume */
>> +		if (key->type == BTRFS_ROOT_BACKREF_KEY ||
>> +		    key->type == BTRFS_ROOT_REF_KEY)
>> +			item_len = sizeof(struct btrfs_root_ref);
>> +
>> +		if (sizeof(sh) + item_len > *buf_size) {
>> +			if (*num_found) {
>> +				ret = 1;
>> +				goto out;
>  This can be a simple return 1;
> 
> 
>> +			}
>> +
>> +			/*
>> +			 * return one empty item back for v1, which does not
>> +			 * handle -EOVERFLOW
>> +			 */
>> +
>> +			*buf_size = sizeof(sh) + item_len;
>> +			item_len = 0;
>> +			ret = -EOVERFLOW;
>> +		}
>> +
>> +		if (sizeof(sh) + item_len + *sk_offset > *buf_size) {
>> +			ret = 1;
>> +			goto out;
> ditto
>> +		}
>> +
>> +		sh.objectid = key->objectid;
>> +		sh.offset = key->offset;
>> +		sh.type = key->type;
>> +		sh.len = item_len;
>> +		sh.transid = found_transid;
>> +
>> +		/* copy search result header */
>> +		if (copy_to_user(ubuf + *sk_offset, &sh, sizeof(sh))) {
>> +			ret = -EFAULT;
>> +			goto out;
> ditto
>> +		}
>> +
>> +		*sk_offset += sizeof(sh);
>> +
>> +		if (item_len) {
>> +			char __user *up = ubuf + *sk_offset;
>> +
>> +			/* copy the item */
>> +			if (read_extent_buffer_to_user(leaf, up,
>> +						       item_off, item_len)) {
>> +				ret = -EFAULT;
>> +				goto out;
> ditto
>> +			}
>> +
>> +			*sk_offset += item_len;
>> +		}
>> +		(*num_found)++;
>> +
>> +		if (ret) /* -EOVERFLOW from above */
>> +			goto out;
> return ret
>> +
>> +		if (*num_found >= sk->nr_items) {
>> +			ret = 1;
>> +			goto out;
> return 1
>> +		}
>> +	}
>> +advance_key:
>> +	ret = 0;
>> +	test.objectid = sk->max_objectid;
>> +	test.type = sk->max_type;
>> +	test.offset = sk->max_offset;
>> +	if (btrfs_comp_cpu_keys(key, &test) >= 0)
>> +		ret = 1;
>> +	else if (key->offset < (u64)-1)
>> +		key->offset++;
>> +	else if (key->type < (u8)-1) {
>> +		key->offset = 0;
>> +		key->type++;
>> +	} else if (key->objectid < (u64)-1) {
>> +		key->offset = 0;
>> +		key->type = 0;
>> +		key->objectid++;
>> +	} else
>> +		ret = 1;
>> +out:
> 
> Given that you are not doing any unwinding of locks or some such I don't
> see any reason for the label at all.
> 
>> +	/*
>> +	 *  0: all items from this leaf copied, continue with next
>> +	 *  1: * more items can be copied, but unused buffer is too small
>> +	 *     * all items were found
>> +	 *     Either way, it will stops the loop which iterates to the next
>> +	 *     leaf
>> +	 *  -EOVERFLOW: item was to large for buffer
>> +	 *  -EFAULT: could not copy extent buffer back to userspace
>> +	 */
> Put the description of the return value above the function definition
>> +	return ret;
>> +}
>> +
>>  static noinline int search_ioctl(struct inode *inode,
>>  				 struct btrfs_ioctl_search_key *sk,
>>  				 size_t *buf_size,
>> @@ -2309,6 +2467,100 @@ static noinline int btrfs_ioctl_ino_lookup(struct file *file,
>>  	return ret;
>>  }
>>  
>> +static noinline int search_subvol(struct inode *inode,
>> +				 struct btrfs_ioctl_search_key *sk,
>> +				 size_t *buf_size,
>> +				 char __user *ubuf)
>> +{
>> +	struct btrfs_fs_info *info = btrfs_sb(inode->i_sb);
>> +	struct btrfs_root *root;
>> +	struct btrfs_key key;
>> +	struct btrfs_path *path;
>> +	unsigned long sk_offset = 0;
>> +	int num_found = 0;
>> +	int ret;
>> +
>> +	path = btrfs_alloc_path();
>> +	if (!path)
>> +		return -ENOMEM;
>> +
>> +	/* search ROOT TREEE */
>> +	key.objectid = BTRFS_ROOT_TREE_OBJECTID;
>> +	key.type = BTRFS_ROOT_ITEM_KEY;
>> +	key.offset = (u64)-1;
>> +	root = btrfs_read_fs_root_no_name(info, &key);
>> +	if (IS_ERR(root)) {
>> +		btrfs_free_path(path);
>> +		return -ENOENT;
>> +	}
> 
> So why do you have to do this, when you can just do :
> struct btrfs_root *root = fs_info->tree_root;
> 
> Looking at the wider codebase, the root tree is referenced directly
> almost all the time. btrfs_read_fs_root_no_name is generally used when
> you have the objectid of a particular subvol root item and you want to
> get that one. But this is not the case here.
Ok, thanks.
Tomohiro Misono

> 
>> +
>> +	key.objectid = sk->min_objectid;
>> +	key.type = sk->min_type;
>> +	key.offset = sk->min_offset;
>> +
>> +	while (1) {
>> +		ret = btrfs_search_forward(root, &key, path, sk->min_transid);
>> +		if (ret != 0) {
>> +			if (ret > 0)
>> +				ret = 0;
>> +			goto err;
>> +		}
>> +
>> +		ret = copy_subvol_item(path, &key, sk, buf_size, ubuf,
>> +				 &sk_offset, &num_found);
>> +		btrfs_release_path(path);
>> +		if (ret)
>> +			break;
>> +	}
>> +
>> +	if (ret > 0)
>> +		ret = 0;
>> +err:
>> +	sk->nr_items = num_found;
>> +	btrfs_free_path(path);
>> +	return ret;
>> +}
>> +
>> +/*
>> + * Unprivileged ioctl for getting subvolume related item.
>> + * The arguments are the same as btrfs_ioctl_tree_search()
>> + * and can be used like tree search ioctl.
>> + *
>> + * Only returns ROOT_ITEM/ROOT_BACKREF/ROOT_REF key of subvolumes
>> + * from root tree. Also, the name of subvolume will be omitted from
>> + * ROOT_BACKREF/ROOT_REF item to prevent name leak.
>> + */
>> +static noinline int btrfs_ioctl_get_subvol_info(struct file *file,
>> +					   void __user *argp)
>> +{
>> +	struct btrfs_ioctl_search_args __user *uargs;
>> +	struct btrfs_ioctl_search_key sk;
>> +	struct inode *inode;
>> +	size_t buf_size;
>> +	int ret;
>> +
>> +	uargs = (struct btrfs_ioctl_search_args __user *)argp;
>> +
>> +	if (copy_from_user(&sk, &uargs->key, sizeof(sk)))
>> +		return -EFAULT;
>> +
>> +	buf_size = sizeof(uargs->buf);
>> +
>> +	inode = file_inode(file);
>> +	ret = search_subvol(inode, &sk, &buf_size, uargs->buf);
>> +
>> +	/*
>> +	 * In the original implementation an overflow is handled by returning a
>> +	 * search header with a len of zero, so reset ret.
>> +	 */
>> +	if (ret == -EOVERFLOW)
>> +		ret = 0;
>> +
>> +	if (ret == 0 && copy_to_user(&uargs->key, &sk, sizeof(sk)))
>> +		ret = -EFAULT;
>> +	return ret;
>> +}
>> +
>>  static noinline int btrfs_ioctl_snap_destroy(struct file *file,
>>  					     void __user *arg)
>>  {
>> @@ -5663,6 +5915,8 @@ 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..1e9361cf66d5 100644
>> --- a/include/uapi/linux/btrfs.h
>> +++ b/include/uapi/linux/btrfs.h
>> @@ -843,5 +843,7 @@ 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 _IOWR(BTRFS_IOCTL_MAGIC, 60, \
>> +					struct btrfs_ioctl_search_args)
>>  
>>  #endif /* _UAPI_LINUX_BTRFS_H */
>>
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Patch
diff mbox

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 111ee282b777..1dba309dce31 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -1921,6 +1921,28 @@  static noinline int key_in_sk(struct btrfs_key *key,
 	return 1;
 }
 
+/*
+ * check if key is in sk and subvolume related range
+ */
+static noinline int key_in_sk_and_subvol(struct btrfs_key *key,
+			      struct btrfs_ioctl_search_key *sk)
+{
+	int ret;
+
+	ret = key_in_sk(key, sk);
+	if (!ret)
+		return 0;
+
+	if ((key->objectid == BTRFS_FS_TREE_OBJECTID ||
+		(key->objectid >= BTRFS_FIRST_FREE_OBJECTID &&
+		 key->objectid <= BTRFS_LAST_FREE_OBJECTID)) &&
+	    key->type >= BTRFS_ROOT_ITEM_KEY &&
+	    key->type <= BTRFS_ROOT_BACKREF_KEY)
+		return 1;
+
+	return 0;
+}
+
 static noinline int copy_to_sk(struct btrfs_path *path,
 			       struct btrfs_key *key,
 			       struct btrfs_ioctl_search_key *sk,
@@ -2045,6 +2067,142 @@  static noinline int copy_to_sk(struct btrfs_path *path,
 	return ret;
 }
 
+/*
+ * Basically the same as copy_to_sk() but restricts the copied item
+ * within subvolume related one using key_in_sk_and_subvol().
+ * Also, the name of subvolume will be omitted from
+ * ROOT_BACKREF/ROOT_REF item.
+ */
+static noinline int copy_subvol_item(struct btrfs_path *path,
+			       struct btrfs_key *key,
+			       struct btrfs_ioctl_search_key *sk,
+			       size_t *buf_size,
+			       char __user *ubuf,
+			       unsigned long *sk_offset,
+			       int *num_found)
+{
+	u64 found_transid;
+	struct extent_buffer *leaf;
+	struct btrfs_ioctl_search_header sh;
+	struct btrfs_key test;
+	unsigned long item_off;
+	unsigned long item_len;
+	int nritems;
+	int i;
+	int slot;
+	int ret = 0;
+
+	leaf = path->nodes[0];
+	slot = path->slots[0];
+	nritems = btrfs_header_nritems(leaf);
+
+	if (btrfs_header_generation(leaf) > sk->max_transid) {
+		i = nritems;
+		goto advance_key;
+	}
+	found_transid = btrfs_header_generation(leaf);
+
+	for (i = slot; i < nritems; i++) {
+		item_off = btrfs_item_ptr_offset(leaf, i);
+		item_len = btrfs_item_size_nr(leaf, i);
+
+		btrfs_item_key_to_cpu(leaf, key, i);
+		if (!key_in_sk_and_subvol(key, sk))
+			continue;
+
+		/* will not copy the name of subvolume */
+		if (key->type == BTRFS_ROOT_BACKREF_KEY ||
+		    key->type == BTRFS_ROOT_REF_KEY)
+			item_len = sizeof(struct btrfs_root_ref);
+
+		if (sizeof(sh) + item_len > *buf_size) {
+			if (*num_found) {
+				ret = 1;
+				goto out;
+			}
+
+			/*
+			 * return one empty item back for v1, which does not
+			 * handle -EOVERFLOW
+			 */
+
+			*buf_size = sizeof(sh) + item_len;
+			item_len = 0;
+			ret = -EOVERFLOW;
+		}
+
+		if (sizeof(sh) + item_len + *sk_offset > *buf_size) {
+			ret = 1;
+			goto out;
+		}
+
+		sh.objectid = key->objectid;
+		sh.offset = key->offset;
+		sh.type = key->type;
+		sh.len = item_len;
+		sh.transid = found_transid;
+
+		/* copy search result header */
+		if (copy_to_user(ubuf + *sk_offset, &sh, sizeof(sh))) {
+			ret = -EFAULT;
+			goto out;
+		}
+
+		*sk_offset += sizeof(sh);
+
+		if (item_len) {
+			char __user *up = ubuf + *sk_offset;
+
+			/* copy the item */
+			if (read_extent_buffer_to_user(leaf, up,
+						       item_off, item_len)) {
+				ret = -EFAULT;
+				goto out;
+			}
+
+			*sk_offset += item_len;
+		}
+		(*num_found)++;
+
+		if (ret) /* -EOVERFLOW from above */
+			goto out;
+
+		if (*num_found >= sk->nr_items) {
+			ret = 1;
+			goto out;
+		}
+	}
+advance_key:
+	ret = 0;
+	test.objectid = sk->max_objectid;
+	test.type = sk->max_type;
+	test.offset = sk->max_offset;
+	if (btrfs_comp_cpu_keys(key, &test) >= 0)
+		ret = 1;
+	else if (key->offset < (u64)-1)
+		key->offset++;
+	else if (key->type < (u8)-1) {
+		key->offset = 0;
+		key->type++;
+	} else if (key->objectid < (u64)-1) {
+		key->offset = 0;
+		key->type = 0;
+		key->objectid++;
+	} else
+		ret = 1;
+out:
+	/*
+	 *  0: all items from this leaf copied, continue with next
+	 *  1: * more items can be copied, but unused buffer is too small
+	 *     * all items were found
+	 *     Either way, it will stops the loop which iterates to the next
+	 *     leaf
+	 *  -EOVERFLOW: item was to large for buffer
+	 *  -EFAULT: could not copy extent buffer back to userspace
+	 */
+	return ret;
+}
+
 static noinline int search_ioctl(struct inode *inode,
 				 struct btrfs_ioctl_search_key *sk,
 				 size_t *buf_size,
@@ -2309,6 +2467,100 @@  static noinline int btrfs_ioctl_ino_lookup(struct file *file,
 	return ret;
 }
 
+static noinline int search_subvol(struct inode *inode,
+				 struct btrfs_ioctl_search_key *sk,
+				 size_t *buf_size,
+				 char __user *ubuf)
+{
+	struct btrfs_fs_info *info = btrfs_sb(inode->i_sb);
+	struct btrfs_root *root;
+	struct btrfs_key key;
+	struct btrfs_path *path;
+	unsigned long sk_offset = 0;
+	int num_found = 0;
+	int ret;
+
+	path = btrfs_alloc_path();
+	if (!path)
+		return -ENOMEM;
+
+	/* search ROOT TREEE */
+	key.objectid = BTRFS_ROOT_TREE_OBJECTID;
+	key.type = BTRFS_ROOT_ITEM_KEY;
+	key.offset = (u64)-1;
+	root = btrfs_read_fs_root_no_name(info, &key);
+	if (IS_ERR(root)) {
+		btrfs_free_path(path);
+		return -ENOENT;
+	}
+
+	key.objectid = sk->min_objectid;
+	key.type = sk->min_type;
+	key.offset = sk->min_offset;
+
+	while (1) {
+		ret = btrfs_search_forward(root, &key, path, sk->min_transid);
+		if (ret != 0) {
+			if (ret > 0)
+				ret = 0;
+			goto err;
+		}
+
+		ret = copy_subvol_item(path, &key, sk, buf_size, ubuf,
+				 &sk_offset, &num_found);
+		btrfs_release_path(path);
+		if (ret)
+			break;
+	}
+
+	if (ret > 0)
+		ret = 0;
+err:
+	sk->nr_items = num_found;
+	btrfs_free_path(path);
+	return ret;
+}
+
+/*
+ * Unprivileged ioctl for getting subvolume related item.
+ * The arguments are the same as btrfs_ioctl_tree_search()
+ * and can be used like tree search ioctl.
+ *
+ * Only returns ROOT_ITEM/ROOT_BACKREF/ROOT_REF key of subvolumes
+ * from root tree. Also, the name of subvolume will be omitted from
+ * ROOT_BACKREF/ROOT_REF item to prevent name leak.
+ */
+static noinline int btrfs_ioctl_get_subvol_info(struct file *file,
+					   void __user *argp)
+{
+	struct btrfs_ioctl_search_args __user *uargs;
+	struct btrfs_ioctl_search_key sk;
+	struct inode *inode;
+	size_t buf_size;
+	int ret;
+
+	uargs = (struct btrfs_ioctl_search_args __user *)argp;
+
+	if (copy_from_user(&sk, &uargs->key, sizeof(sk)))
+		return -EFAULT;
+
+	buf_size = sizeof(uargs->buf);
+
+	inode = file_inode(file);
+	ret = search_subvol(inode, &sk, &buf_size, uargs->buf);
+
+	/*
+	 * In the original implementation an overflow is handled by returning a
+	 * search header with a len of zero, so reset ret.
+	 */
+	if (ret == -EOVERFLOW)
+		ret = 0;
+
+	if (ret == 0 && copy_to_user(&uargs->key, &sk, sizeof(sk)))
+		ret = -EFAULT;
+	return ret;
+}
+
 static noinline int btrfs_ioctl_snap_destroy(struct file *file,
 					     void __user *arg)
 {
@@ -5663,6 +5915,8 @@  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..1e9361cf66d5 100644
--- a/include/uapi/linux/btrfs.h
+++ b/include/uapi/linux/btrfs.h
@@ -843,5 +843,7 @@  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 _IOWR(BTRFS_IOCTL_MAGIC, 60, \
+					struct btrfs_ioctl_search_args)
 
 #endif /* _UAPI_LINUX_BTRFS_H */