[v4,1/3] btrfs: Add unprivileged ioctl which returns subvolume information
diff mbox

Message ID f0784a42dda08a596fcea31de73179dad5987d64.1526002757.git.misono.tomohiro@jp.fujitsu.com
State New
Headers show

Commit Message

Misono Tomohiro May 11, 2018, 7:26 a.m. UTC
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@jp.fujitsu.com>
---
 fs/btrfs/ioctl.c           | 129 +++++++++++++++++++++++++++++++++++++++++++++
 include/uapi/linux/btrfs.h |  51 ++++++++++++++++++
 2 files changed, 180 insertions(+)

Comments

Misono Tomohiro May 15, 2018, 7:03 a.m. UTC | #1
On 2018/05/15 15:31, Gu, Jinxiang/顾 金香 wrote:
> Hi,
> 
>> -----Original Message-----
>> From: linux-btrfs-owner@vger.kernel.org [mailto:linux-btrfs-owner@vger.kernel.org] On Behalf Of Tomohiro Misono
>> Sent: Friday, May 11, 2018 3:26 PM
>> To: linux-btrfs@vger.kernel.org
>> Subject: [PATCH v4 1/3] btrfs: Add unprivileged ioctl which returns subvolume information
>>
>> 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@jp.fujitsu.com>
>> ---
>>  fs/btrfs/ioctl.c           | 129 +++++++++++++++++++++++++++++++++++++++++++++
>>  include/uapi/linux/btrfs.h |  51 ++++++++++++++++++
>>  2 files changed, 180 insertions(+)
>>
>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index 48e2ddff32bd..64b23e22852f 100644
>> --- a/fs/btrfs/ioctl.c
>> +++ b/fs/btrfs/ioctl.c
>> @@ -2242,6 +2242,133 @@ 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);
>> +	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)
>> +				return ret;
> Should goto out; to free subvol_info and path.
Thanks, will update both.

>> +		}
>> +
>> +		/* 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);
>> +	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)
>> +			return ret;
> Should goto out; to free subvol_info and path.
>> +	}
>> +
>> +	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);
>> +	}
> If this if is not correct(ex. corrupt filesystem without backref),
> should it return -ENOENT, or its be ok without parent_id, dirid and name.
> Suggest to add logic of else.

If backref does not exist (except top-level subvolume), it means filesystem corruption.
So, I'd like to return  -EUCLEAN here.

Thanks,
Tomohiro Misono

> 
>> +
>> +	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 +5501,8 @@ 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..ed053852c71f 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 filed 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 */
>> --
>> 2.14.3
>>
> 
> Reviewed-by: Gu Jinxiang <gujx@cn.fujitsu.com>
>>
>> --
>> To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
>> the body of a message to majordomo@vger.kernel.org
>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>
> 

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Misono Tomohiro May 16, 2018, 5:42 a.m. UTC | #2
On 2018/05/15 16:57, Gu, Jinxiang/顾 金香 wrote:
> Hi, add a missed a comment.
> 
>> -----Original Message-----
>> From: Misono Tomohiro [mailto:misono.tomohiro@jp.fujitsu.com]
>> Sent: Tuesday, May 15, 2018 3:04 PM
>> To: Gu, Jinxiang/顾 金香 <gujx@cn.fujitsu.com>; linux-btrfs@vger.kernel.org
>> Subject: Re: [PATCH v4 1/3] btrfs: Add unprivileged ioctl which returns subvolume information
>>
>> On 2018/05/15 15:31, Gu, Jinxiang/顾 金香 wrote:
>>> Hi,
>>>
>>>> -----Original Message-----
>>>> From: linux-btrfs-owner@vger.kernel.org
>>>> [mailto:linux-btrfs-owner@vger.kernel.org] On Behalf Of Tomohiro
>>>> Misono
>>>> Sent: Friday, May 11, 2018 3:26 PM
>>>> To: linux-btrfs@vger.kernel.org
>>>> Subject: [PATCH v4 1/3] btrfs: Add unprivileged ioctl which returns
>>>> subvolume information
>>>>
>>>> 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@jp.fujitsu.com>
>>>> ---
>>>>  fs/btrfs/ioctl.c           | 129 +++++++++++++++++++++++++++++++++++++++++++++
>>>>  include/uapi/linux/btrfs.h |  51 ++++++++++++++++++
>>>>  2 files changed, 180 insertions(+)
>>>>
>>>> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c index
>>>> 48e2ddff32bd..64b23e22852f 100644
>>>> --- a/fs/btrfs/ioctl.c
>>>> +++ b/fs/btrfs/ioctl.c
>>>> @@ -2242,6 +2242,133 @@ 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);
>>>> +	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)
>>>> +				return ret;
>>> Should goto out; to free subvol_info and path.
>> Thanks, will update both.
>>
> 
> Since btrfs_next_leaf may return 1 when nritems of next leaf is 0,
> So, btrfs_item_key_to_cpu(path->nodes[0], &key, path->slots[0]); may goes wrong.
> And I think it should add a judge before btrfs_item_key_to_cpu.

Ok, I will update to handle all cases.

[snip]>>>> +	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);
>>>> +	}
>>> If this if is not correct(ex. corrupt filesystem without backref),
>>> should it return -ENOENT, or its be ok without parent_id, dirid and name.
>>> Suggest to add logic of else.
>>
>> If backref does not exist (except top-level subvolume), it means filesystem corruption.
>> So, I'd like to return  -EUCLEAN here.

On second thought, I notice if this ioctl is called after containing subvolume is deleted,
the entry may not exist. So, -ENOENT is fine.

Thanks,
Tomohiro Misono

>>
>> Thanks,
>> Tomohiro Misono
>>
>>>
>>>> +
>>>> +	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 +5501,8 @@ 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..ed053852c71f 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 filed 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 */
>>>> --
>>>> 2.14.3
>>>>
>>>
>>> Reviewed-by: Gu Jinxiang <gujx@cn.fujitsu.com>
>>>>
>>>> --
>>>> To unsubscribe from this list: send the line "unsubscribe
>>>> linux-btrfs" in the body of a message to majordomo@vger.kernel.org
>>>> More majordomo info at  http://vger.kernel.org/majordomo-info.html
>>>>
>>>

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Patch
diff mbox

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 48e2ddff32bd..64b23e22852f 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2242,6 +2242,133 @@  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);
+	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)
+				return ret;
+		}
+
+		/* 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);
+	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)
+			return ret;
+	}
+
+	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);
+	}
+
+	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 +5501,8 @@  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..ed053852c71f 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 filed 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 */