354 lines
9.9 KiB
ReStructuredText
354 lines
9.9 KiB
ReStructuredText
btrfs-ioctl(3)
|
|
==============
|
|
|
|
NAME
|
|
----
|
|
|
|
btrfs-ioctl - documentation for the ioctl interface to btrfs
|
|
|
|
DESCRIPTION
|
|
-----------
|
|
|
|
The ioctl() system call is a way how to request custom actions performed on a
|
|
filesystem beyond the standard interfaces (like syscalls). An ioctl is
|
|
specified by a number and an associated data structure that implement a
|
|
feature, usually not available in other filesystems. The number of ioctls grows
|
|
over time and in some cases get promoted to a VFS-level ioctl once other
|
|
filesystems adopt the functionality. Backward compatibility is maintained
|
|
and a formerly private ioctl number could become available on the VFS level.
|
|
|
|
|
|
DATA STRUCTURES AND DEFINITIONS
|
|
-------------------------------
|
|
|
|
.. code-block::
|
|
|
|
struct btrfs_ioctl_vol_args {
|
|
__s64 fd;
|
|
char name[BTRFS_PATH_NAME_MAX + 1];
|
|
};
|
|
|
|
.. code-block::
|
|
|
|
struct btrfs_ioctl_vol_args_v2 {
|
|
__s64 fd;
|
|
__u64 transid;
|
|
__u64 flags;
|
|
union {
|
|
struct {
|
|
__u64 size;
|
|
struct btrfs_qgroup_inherit __user *qgroup_inherit;
|
|
};
|
|
__u64 unused[4];
|
|
};
|
|
union {
|
|
char name[BTRFS_SUBVOL_NAME_MAX + 1];
|
|
__u64 devid;
|
|
__u64 subvolid;
|
|
};
|
|
};
|
|
|
|
.. code-block::
|
|
|
|
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];
|
|
};
|
|
|
|
.. code-block::
|
|
|
|
BTRFS_SUBVOL_NAME_MAX = 4039
|
|
BTRFS_PATH_NAME_MAX = 4087
|
|
|
|
OVERVIEW
|
|
--------
|
|
|
|
The ioctls are defined by a number and associated with a data structure that
|
|
contains further information. All ioctls use file descriptor (fd) as a reference
|
|
point, it could be the filesystem or a directory inside the filesystem.
|
|
|
|
An ioctl can be used in the following schematic way:
|
|
|
|
.. code-block::
|
|
|
|
struct btrfs_ioctl_args args;
|
|
|
|
memset(&args, 0, sizeof(args));
|
|
args.key = value;
|
|
ret = ioctl(fd, BTRFS_IOC_NUMBER, &args);
|
|
|
|
The 'fd' is the entry point to the filesystem and for most ioctls it does not
|
|
matter which file or directory is that. Where it matters it's explicitly
|
|
mentioned. The 'args' is the associated data structure for the request. It's
|
|
strongly recommended to initialize the whole structure to zeros as this is
|
|
future-proof when the ioctl gets further extensions. Not doing that could lead
|
|
to mismatch of old userspace and new kernel versions, or vice versa.
|
|
The 'BTRFS_IOC_NUMBER' is says which operation should be done on the given
|
|
arguments. Some ioctls take a specific data structure, some of them share a
|
|
common one, no argument structure ioctls exist too.
|
|
|
|
The library 'libbtrfsutil' wraps a few ioctls for convenience. Using raw ioctls
|
|
is not discouraged but may be cumbersome though it does not need additional
|
|
library dependency. Backward compatibility is guaranteed and incompatible
|
|
changes usually lead to a new version of the ioctl. Enhancements of existing
|
|
ioctls can happen and depend on additional flags to be set. Zeroed unused
|
|
space is commonly understood as a mechanism to communicate the compatibility
|
|
between kernel and userspace and thus zeroing is really important. In exceptional
|
|
cases this is not enough and further flags need to be passed to distinguish
|
|
between zero as implicit unused initialization and a valid zero value. Such
|
|
cases are documented.
|
|
|
|
LIST OF IOCTLS
|
|
--------------
|
|
|
|
* BTRFS_IOC_SUBVOL_CREATE -- (obsolete) create a subvolume
|
|
* BTRFS_IOC_SNAP_CREATE
|
|
* BTRFS_IOC_DEFRAG
|
|
* BTRFS_IOC_RESIZE
|
|
* BTRFS_IOC_SCAN_DEV
|
|
* BTRFS_IOC_SYNC
|
|
* BTRFS_IOC_CLONE
|
|
* BTRFS_IOC_ADD_DEV
|
|
* BTRFS_IOC_RM_DEV
|
|
* BTRFS_IOC_BALANCE
|
|
* BTRFS_IOC_CLONE_RANGE
|
|
* BTRFS_IOC_SUBVOL_CREATE
|
|
* BTRFS_IOC_SNAP_DESTROY
|
|
* BTRFS_IOC_DEFRAG_RANGE
|
|
* BTRFS_IOC_TREE_SEARCH
|
|
* BTRFS_IOC_TREE_SEARCH_V2
|
|
* BTRFS_IOC_INO_LOOKUP
|
|
* BTRFS_IOC_DEFAULT_SUBVOL
|
|
* BTRFS_IOC_SPACE_INFO
|
|
* BTRFS_IOC_START_SYNC
|
|
* BTRFS_IOC_WAIT_SYNC
|
|
* BTRFS_IOC_SNAP_CREATE_V2 -- create a snapshot of a subvolume
|
|
* BTRFS_IOC_SUBVOL_CREATE_V2 -- create a subvolume
|
|
* BTRFS_IOC_SUBVOL_GETFLAGS -- get flags of a subvolume
|
|
* BTRFS_IOC_SUBVOL_SETFLAGS -- set flags of a subvolume
|
|
* BTRFS_IOC_SCRUB
|
|
* BTRFS_IOC_SCRUB_CANCEL
|
|
* BTRFS_IOC_SCRUB_PROGRESS
|
|
* BTRFS_IOC_DEV_INFO
|
|
* BTRFS_IOC_FS_INFO
|
|
* BTRFS_IOC_BALANCE_V2
|
|
* BTRFS_IOC_BALANCE_CTL
|
|
* BTRFS_IOC_BALANCE_PROGRESS
|
|
* BTRFS_IOC_INO_PATHS
|
|
* BTRFS_IOC_LOGICAL_INO
|
|
* BTRFS_IOC_SET_RECEIVED_SUBVOL
|
|
* BTRFS_IOC_SEND
|
|
* BTRFS_IOC_DEVICES_READY
|
|
* BTRFS_IOC_QUOTA_CTL
|
|
* BTRFS_IOC_QGROUP_ASSIGN
|
|
* BTRFS_IOC_QGROUP_CREATE
|
|
* BTRFS_IOC_QGROUP_LIMIT
|
|
* BTRFS_IOC_QUOTA_RESCAN
|
|
* BTRFS_IOC_QUOTA_RESCAN_STATUS
|
|
* BTRFS_IOC_QUOTA_RESCAN_WAIT
|
|
* BTRFS_IOC_GET_FSLABEL
|
|
* BTRFS_IOC_SET_FSLABEL
|
|
* BTRFS_IOC_GET_DEV_STATS
|
|
* BTRFS_IOC_DEV_REPLACE
|
|
* BTRFS_IOC_FILE_EXTENT_SAME
|
|
* BTRFS_IOC_GET_FEATURES
|
|
* BTRFS_IOC_SET_FEATURES
|
|
* BTRFS_IOC_GET_SUPPORTED_FEATURES
|
|
* BTRFS_IOC_RM_DEV_V2
|
|
* BTRFS_IOC_LOGICAL_INO_V2
|
|
* BTRFS_IOC_GET_SUBVOL_INFO -- get information about a subvolume
|
|
* BTRFS_IOC_GET_SUBVOL_ROOTREF
|
|
* BTRFS_IOC_INO_LOOKUP_USER
|
|
* BTRFS_IOC_SNAP_DESTROY_V2 -- destroy a (snapshot or regular) subvolume
|
|
|
|
DETAILED DESCRIPTION
|
|
--------------------
|
|
|
|
BTRFS_IOC_SUBVOL_CREATE
|
|
~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
.. note::
|
|
obsoleted by BTRFS_IOC_SUBVOL_CREATE_V2
|
|
|
|
*(since: 3.0, obsoleted: 4.0)* Create a subvolume.
|
|
|
|
ioctl fd
|
|
file descriptor of the parent directory of the new subvolume
|
|
argument type
|
|
struct btrfs_ioctl_vol_args
|
|
fd
|
|
ignored
|
|
name
|
|
name of the subvolume, although the buffer can be almost 4k, the file
|
|
size is limited by Linux VFS to 255 characters and must not contain a slash
|
|
('/')
|
|
|
|
BTRFS_IOC_SNAP_CREATE_V2
|
|
~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
.. note::
|
|
obsoletes BTRFS_IOC_SNAP_CREATE
|
|
|
|
Create a snapshot of a subvolume.
|
|
|
|
ioctl fd
|
|
file descriptor of the directory inside which to create the new snapshot
|
|
argument type
|
|
struct btrfs_ioctl_vol_args_v2
|
|
fd
|
|
file descriptor of any directory inside the subvolume to snapshot
|
|
transid
|
|
ignored
|
|
flags
|
|
any subset of `BTRFS_SUBVOL_RDONLY` to make the new snapshot read-only, or
|
|
`BTRFS_SUBVOL_QGROUP_INHERIT` to apply the `qgroup_inherit` field
|
|
name
|
|
the name, under the ioctl fd, for the new subvolume
|
|
|
|
BTRFS_IOC_SUBVOL_CREATE_V2
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
.. note::
|
|
obsoletes BTRFS_IOC_SUBVOL_CREATE
|
|
|
|
*(since: 3.6)* Create a subvolume, qgroup inheritance can be specified.
|
|
|
|
ioctl fd
|
|
file descriptor of the parent directory of the new subvolume
|
|
argument type
|
|
struct btrfs_ioctl_vol_args_v2
|
|
fd
|
|
ignored
|
|
transid
|
|
ignored
|
|
flags
|
|
ignored
|
|
size
|
|
...
|
|
qgroup_inherit
|
|
...
|
|
name
|
|
name of the subvolume, although the buffer can be almost 4k, the file size
|
|
is limited by Linux VFS to 255 characters and must not contain a slash ('/')
|
|
devid
|
|
...
|
|
|
|
BTRFS_IOC_SUBVOL_GETFLAGS
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Read the flags of a subvolume. The returned flags are either 0 or
|
|
`BTRFS_SUBVOL_RDONLY`.
|
|
|
|
ioctl fd
|
|
file descriptor of the subvolume to examine
|
|
argument type
|
|
uint64_t
|
|
|
|
BTRFS_IOC_SUBVOL_SETFLAGS
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Change the flags of a subvolume.
|
|
|
|
ioctl fd
|
|
file descriptor of the subvolume to modify
|
|
argument type
|
|
uint64_t, either 0 or `BTRFS_SUBVOL_RDONLY`
|
|
|
|
BTRFS_IOC_GET_SUBVOL_INFO
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Get information about a subvolume.
|
|
|
|
ioctl fd
|
|
file descriptor of the subvolume to examine
|
|
argument type
|
|
struct btrfs_ioctl_get_subvol_info_args
|
|
|
|
BTRFS_IOC_SNAP_DESTROY_V2
|
|
~~~~~~~~~~~~~~~~~~~~~~~~~
|
|
|
|
Destroy a subvolume, which may or may not be a snapshot.
|
|
|
|
ioctl fd
|
|
if `flags` does not include `BTRFS_SUBVOL_SPEC_BY_ID`, or if executing in a
|
|
non-root user namespace, file descriptor of the parent directory containing
|
|
the subvolume to delete; otherwise, file descriptor of any directory on the
|
|
same filesystem as the subvolume to delete, but not within the same
|
|
subvolume
|
|
argument type
|
|
struct btrfs_ioctl_vol_args_v2
|
|
fd
|
|
ignored
|
|
transid
|
|
ignored
|
|
flags
|
|
0 if the `name` field identifies the subvolume by name in the specified
|
|
directory, or `BTRFS_SUBVOL_SPEC_BY_ID` if the `subvolid` field specifies
|
|
the ID of the subvolume
|
|
name
|
|
only if `flags` does not contain `BTRFS_SUBVOL_SPEC_BY_ID`, the name
|
|
(within the directory identified by `fd`) of the subvolume to delete
|
|
subvolid
|
|
only if `flags` contains `BTRFS_SUBVOL_SPEC_BY_ID`, the subvolume ID of the
|
|
subvolume to delete
|
|
|
|
AVAILABILITY
|
|
------------
|
|
|
|
**btrfs** is part of btrfs-progs. Please refer to the documentation at
|
|
`https://btrfs.readthedocs.io <https://btrfs.readthedocs.io>`_.
|
|
|
|
SEE ALSO
|
|
--------
|
|
ioctl(2)
|