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btrfs: Add unprivileged ioctl which returns subvolume information
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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.)

Reviewed-by: Gu Jinxiang <gujx@cn.fujitsu.com>
Tested-by: Gu Jinxiang <gujx@cn.fujitsu.com>
Signed-off-by: Tomohiro Misono <misono.tomohiro@jp.fujitsu.com>
[ minor style fixes, update struct comments ]
Signed-off-by: David Sterba <dsterba@suse.com>
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Tomohiro Misono authored and David Sterba committed May 31, 2018
1 parent ad7e1a7 commit b64ec07
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121 changes: 121 additions & 0 deletions fs/btrfs/ioctl.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2383,6 +2383,125 @@ 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 int btrfs_ioctl_get_subvol_info(struct file *file, void __user *argp)
{
struct btrfs_ioctl_get_subvol_info_args *subvol_info;
struct btrfs_fs_info *fs_info;
struct btrfs_root *root;
struct btrfs_path *path;
struct btrfs_key key;
struct btrfs_root_item *root_item;
struct btrfs_root_ref *rref;
struct extent_buffer *leaf;
unsigned long item_off;
unsigned long item_len;
struct inode *inode;
int slot;
int ret = 0;

path = btrfs_alloc_path();
if (!path)
return -ENOMEM;

subvol_info = kzalloc(sizeof(*subvol_info), GFP_KERNEL);
if (!subvol_info) {
btrfs_free_path(path);
return -ENOMEM;
}

inode = file_inode(file);
fs_info = BTRFS_I(inode)->root->fs_info;

/* Get root_item of inode's subvolume */
key.objectid = BTRFS_I(inode)->root->root_key.objectid;
key.type = BTRFS_ROOT_ITEM_KEY;
key.offset = (u64)-1;
root = btrfs_read_fs_root_no_name(fs_info, &key);
if (IS_ERR(root)) {
ret = PTR_ERR(root);
goto out;
}
root_item = &root->root_item;

subvol_info->treeid = 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);

if (key.objectid != BTRFS_FS_TREE_OBJECTID) {
/* Search root tree for ROOT_BACKREF of this subvolume */
root = fs_info->tree_root;

key.type = BTRFS_ROOT_BACKREF_KEY;
key.offset = 0;
ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
if (ret < 0) {
goto out;
} else if (path->slots[0] >=
btrfs_header_nritems(path->nodes[0])) {
ret = btrfs_next_leaf(root, path);
if (ret < 0) {
goto out;
} else if (ret > 0) {
ret = -EUCLEAN;
goto out;
}
}

leaf = path->nodes[0];
slot = path->slots[0];
btrfs_item_key_to_cpu(leaf, &key, slot);
if (key.objectid == subvol_info->treeid &&
key.type == BTRFS_ROOT_BACKREF_KEY) {
subvol_info->parent_id = key.offset;

rref = btrfs_item_ptr(leaf, slot, struct btrfs_root_ref);
subvol_info->dirid = btrfs_root_ref_dirid(leaf, rref);

item_off = btrfs_item_ptr_offset(leaf, slot)
+ sizeof(struct btrfs_root_ref);
item_len = btrfs_item_size_nr(leaf, slot)
- sizeof(struct btrfs_root_ref);
read_extent_buffer(leaf, 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:
btrfs_free_path(path);
kzfree(subvol_info);
return ret;
}

static noinline int btrfs_ioctl_snap_destroy(struct file *file,
void __user *arg)
{
Expand Down Expand Up @@ -5545,6 +5664,8 @@ long btrfs_ioctl(struct file *file, unsigned int
return btrfs_ioctl_fsgetxattr(file, argp);
case FS_IOC_FSSETXATTR:
return btrfs_ioctl_fssetxattr(file, argp);
case BTRFS_IOC_GET_SUBVOL_INFO:
return btrfs_ioctl_get_subvol_info(file, argp);
}

return -ENOTTY;
Expand Down
62 changes: 62 additions & 0 deletions include/uapi/linux/btrfs.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -725,6 +725,66 @@ struct btrfs_ioctl_send_args {
__u64 reserved[4]; /* in */
};

/*
* Information about a fs tree root.
*
* All items are filled by the ioctl
*/
struct btrfs_ioctl_get_subvol_info_args {
/* Id of this subvolume */
__u64 treeid;

/* 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 a deleted subvolume.
*/
__u64 parent_id;

/*
* Inode number of the directory which contains this subvolume.
* Zero for top-level subvolume or a 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 a non-snapshot subvolume.
*/
__u8 parent_uuid[BTRFS_UUID_SIZE];

/*
* UUID of the subvolume from which this subvolume was received.
* All zero for non-received subvolume.
*/
__u8 received_uuid[BTRFS_UUID_SIZE];

/* Transaction id indicating when change/create/send/receive happened */
__u64 ctransid;
__u64 otransid;
__u64 stransid;
__u64 rtransid;
/* Time corresponding 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;

/* Must be zero */
__u64 reserved[8];
};

/* Error codes as returned by the kernel */
enum btrfs_err_code {
BTRFS_ERROR_DEV_RAID1_MIN_NOT_MET = 1,
Expand Down Expand Up @@ -843,5 +903,7 @@ 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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