Ioctl Numbers

19 October 1999

Michael Elizabeth Chastain <mec@shout.net>

If you are adding new ioctl’s to the kernel, you should use the _IO macros defined in <linux/ioctl.h>:

macro	parameters
_IO	none
_IOW	write (read from userspace)
_IOR	read (write to userspace)
_IOWR	write and read

‘Write’ and ‘read’ are from the user’s point of view, just like the system calls ‘write’ and ‘read’. For example, a SET_FOO ioctl would be _IOW, although the kernel would actually read data from user space; a GET_FOO ioctl would be _IOR, although the kernel would actually write data to user space.

The first argument to the macros is an identifying letter or number from the table below. Because of the large number of drivers, many drivers share a partial letter with other drivers.

If you are writing a driver for a new device and need a letter, pick an unused block with enough room for expansion: 32 to 256 ioctl commands should suffice. You can register the block by patching this file and submitting the patch through usual patch submission process.

The second argument is a sequence number to distinguish ioctls from each other. The third argument (not applicable to _IO) is the type of the data going into the kernel or coming out of the kernel (e.g. ‘int’ or ‘struct foo’).

Note

Do NOT use sizeof(arg) as the third argument as this results in your ioctl thinking it passes an argument of type size_t.

Some devices use their major number as the identifier; this is OK, as long as it is unique. Some devices are irregular and don’t follow any convention at all.

Following this convention is good because:

1. Keeping the ioctl’s globally unique helps error checking: if a program calls an ioctl on the wrong device, it will get an error rather than some unexpected behaviour.

2. The ‘strace’ build procedure automatically finds ioctl numbers defined with the macros.

3. ‘strace’ can decode numbers back into useful names when the numbers are unique.

4. People looking for ioctls can grep for them more easily when this convention is used to define the ioctl numbers.

5. When following the convention, the driver code can use generic code to copy the parameters between user and kernel space.

This table lists ioctls visible from userland, excluding ones from drivers/staging/.

Code	Seq# (hex)	Include File	Comments
0x00	00-1F	linux/fs.h	conflict!
0x00	00-1F	scsi/scsi_ioctl.h	conflict!
0x00	00-1F	linux/fb.h	conflict!
0x00	00-1F	linux/wavefront.h	conflict!
0x02	all	linux/fd.h
0x03	all	linux/hdreg.h
0x04	D2-DC	linux/umsdos_fs.h	Dead since 2.6.11, but don’t reuse these.
0x06	all	linux/lp.h
0x07	9F-D0	linux/vmw_vmci_defs.h, uapi/linux/vm_sockets.h
0x09	all	linux/raid/md_u.h
0x10	00-0F	drivers/char/s390/vmcp.h
0x10	10-1F	arch/s390/include/uapi/sclp_ctl.h
0x10	20-2F	arch/s390/include/uapi/asm/hypfs.h
0x12	all	linux/fs.h linux/blkpg.h linux/blkzoned.h linux/blk-crypto.h	BLK* ioctls
0x15	all	linux/fs.h	FS_IOC_* ioctls
0x1b	all		InfiniBand Subsystem <http://infiniband.sourceforge.net/>
0x20	all	drivers/cdrom/cm206.h
0x22	all	scsi/sg.h
0x3E	00-0F	linux/counter.h	<mailto:linux-iio@vger.kernel.org>
‘!’	00-1F	uapi/linux/seccomp.h
‘#’	00-3F		IEEE 1394 Subsystem Block for the entire subsystem
‘$’	00-0F	linux/perf_counter.h, linux/perf_event.h
‘%’	00-0F	include/uapi/linux/stm.h	System Trace Module subsystem <mailto:alexander.shishkin@linux.intel.com>
‘&’	00-07	drivers/firewire/nosy-user.h
‘*’	00-1F	uapi/linux/user_events.h	User Events Subsystem <mailto:linux-trace-kernel@vger.kernel.org>
‘1’	00-1F	linux/timepps.h	PPS kit from Ulrich Windl <ftp://ftp.de.kernel.org/pub/linux/daemons/ntp/PPS/>
‘2’	01-04	linux/i2o.h
‘3’	00-0F	drivers/s390/char/raw3270.h	conflict!
‘3’	00-1F	linux/suspend_ioctls.h, kernel/power/user.c	conflict!
‘8’	all		SNP8023 advanced NIC card <mailto:mcr@solidum.com>
‘;’	64-7F	linux/vfio.h
‘;’	80-FF	linux/iommufd.h
‘=’	00-3f	uapi/linux/ptp_clock.h	<mailto:richardcochran@gmail.com>
‘@’	00-0F	linux/radeonfb.h	conflict!
‘@’	00-0F	drivers/video/aty/aty128fb.c	conflict!
‘A’	00-1F	linux/apm_bios.h	conflict!
‘A’	00-0F	linux/agpgart.h, drivers/char/agp/compat_ioctl.h	conflict!
‘A’	00-7F	sound/asound.h	conflict!
‘B’	00-1F	linux/cciss_ioctl.h	conflict!
‘B’	00-0F	include/linux/pmu.h	conflict!
‘B’	C0-FF	advanced bbus	<mailto:maassen@uni-freiburg.de>
‘B’	00-0F	xen/xenbus_dev.h	conflict!
‘C’	all	linux/soundcard.h	conflict!
‘C’	01-2F	linux/capi.h	conflict!
‘C’	F0-FF	drivers/net/wan/cosa.h	conflict!
‘D’	all	arch/s390/include/asm/dasd.h
‘D’	40-5F	drivers/scsi/dpt/dtpi_ioctl.h	Dead since 2022
‘D’	05	drivers/scsi/pmcraid.h
‘E’	all	linux/input.h	conflict!
‘E’	00-0F	xen/evtchn.h	conflict!
‘F’	all	linux/fb.h	conflict!
‘F’	01-02	drivers/scsi/pmcraid.h	conflict!
‘F’	20	drivers/video/fsl-diu-fb.h	conflict!
‘F’	20	linux/ivtvfb.h	conflict!
‘F’	20	linux/matroxfb.h	conflict!
‘F’	20	drivers/video/aty/atyfb_base.c	conflict!
‘F’	00-0F	video/da8xx-fb.h	conflict!
‘F’	80-8F	linux/arcfb.h	conflict!
‘F’	DD	video/sstfb.h	conflict!
‘G’	00-3F	drivers/misc/sgi-gru/grulib.h	conflict!
‘G’	00-0F	xen/gntalloc.h, xen/gntdev.h	conflict!
‘H’	00-7F	linux/hiddev.h	conflict!
‘H’	00-0F	linux/hidraw.h	conflict!
‘H’	01	linux/mei.h	conflict!
‘H’	02	linux/mei.h	conflict!
‘H’	03	linux/mei.h	conflict!
‘H’	00-0F	sound/asound.h	conflict!
‘H’	20-40	sound/asound_fm.h	conflict!
‘H’	80-8F	sound/sfnt_info.h	conflict!
‘H’	10-8F	sound/emu10k1.h	conflict!
‘H’	10-1F	sound/sb16_csp.h	conflict!
‘H’	10-1F	sound/hda_hwdep.h	conflict!
‘H’	40-4F	sound/hdspm.h	conflict!
‘H’	40-4F	sound/hdsp.h	conflict!
‘H’	90	sound/usb/usx2y/usb_stream.h
‘H’	00-0F	uapi/misc/habanalabs.h	conflict!
‘H’	A0	uapi/linux/usb/cdc-wdm.h
‘H’	C0-F0	net/bluetooth/hci.h	conflict!
‘H’	C0-DF	net/bluetooth/hidp/hidp.h	conflict!
‘H’	C0-DF	net/bluetooth/cmtp/cmtp.h	conflict!
‘H’	C0-DF	net/bluetooth/bnep/bnep.h	conflict!
‘H’	F1	linux/hid-roccat.h	<mailto:erazor_de@users.sourceforge.net>
‘H’	F8-FA	sound/firewire.h
‘I’	all	linux/isdn.h	conflict!
‘I’	00-0F	drivers/isdn/divert/isdn_divert.h	conflict!
‘I’	40-4F	linux/mISDNif.h	conflict!
‘K’	all	linux/kd.h
‘L’	00-1F	linux/loop.h	conflict!
‘L’	10-1F	drivers/scsi/mpt3sas/mpt3sas_ctl.h	conflict!
‘L’	E0-FF	linux/ppdd.h	encrypted disk device driver <http://linux01.gwdg.de/~alatham/ppdd.html>
‘M’	all	linux/soundcard.h	conflict!
‘M’	01-16 and	mtd/mtd-abi.h drivers/mtd/mtdchar.c	conflict!
‘M’	01-03	drivers/scsi/megaraid/megaraid_sas.h
‘M’	00-0F	drivers/video/fsl-diu-fb.h	conflict!
‘N’	00-1F	drivers/usb/scanner.h
‘N’	40-7F	drivers/block/nvme.c
‘N’	80-8F	uapi/linux/ntsync.h	NT synchronization primitives <mailto:wine-devel@winehq.org>
‘O’	00-06	mtd/ubi-user.h	UBI
‘P’	all	linux/soundcard.h	conflict!
‘P’	60-6F	sound/sscape_ioctl.h	conflict!
‘P’	00-0F	drivers/usb/class/usblp.c	conflict!
‘P’	01-09	drivers/misc/pci_endpoint_test.c	conflict!
‘P’	00-0F	xen/privcmd.h	conflict!
‘P’	00-05	linux/tps6594_pfsm.h	conflict!
‘Q’	all	linux/soundcard.h
‘R’	00-1F	linux/random.h	conflict!
‘R’	01	linux/rfkill.h	conflict!
‘R’	20-2F	linux/trace_mmap.h
‘R’	C0-DF	net/bluetooth/rfcomm.h
‘R’	E0	uapi/linux/fsl_mc.h
‘S’	all	linux/cdrom.h	conflict!
‘S’	80-81	scsi/scsi_ioctl.h	conflict!
‘S’	82-FF	scsi/scsi.h	conflict!
‘S’	00-7F	sound/asequencer.h	conflict!
‘T’	all	linux/soundcard.h	conflict!
‘T’	00-AF	sound/asound.h	conflict!
‘T’	all	arch/x86/include/asm/ioctls.h	conflict!
‘T’	C0-DF	linux/if_tun.h	conflict!
‘U’	all	sound/asound.h	conflict!
‘U’	00-CF	linux/uinput.h	conflict!
‘U’	00-EF	linux/usbdevice_fs.h
‘U’	C0-CF	drivers/bluetooth/hci_uart.h
‘V’	all	linux/vt.h	conflict!
‘V’	all	linux/videodev2.h	conflict!
‘V’	C0	linux/ivtvfb.h	conflict!
‘V’	C0	linux/ivtv.h	conflict!
‘V’	C0	media/si4713.h	conflict!
‘W’	00-1F	linux/watchdog.h	conflict!
‘W’	00-1F	linux/wanrouter.h	conflict! (pre 3.9)
‘W’	00-3F	sound/asound.h	conflict!
‘W’	40-5F	drivers/pci/switch/switchtec.c
‘W’	60-61	linux/watch_queue.h
‘X’	all	fs/xfs/xfs_fs.h, fs/xfs/linux-2.6/xfs_ioctl32.h, include/linux/falloc.h, linux/fs.h,	conflict!
‘X’	all	fs/ocfs2/ocfs_fs.h	conflict!
‘Z’	14-15	drivers/message/fusion/mptctl.h
‘[’	00-3F	linux/usb/tmc.h	USB Test and Measurement Devices <mailto:gregkh@linuxfoundation.org>
‘a’	all	linux/atm*.h, linux/sonet.h	ATM on linux <http://lrcwww.epfl.ch/>
‘b’	00-FF		conflict! bit3 vme host bridge <mailto:natalia@nikhefk.nikhef.nl>
‘b’	00-0F	linux/dma-buf.h	conflict!
‘c’	00-7F	linux/comstats.h	conflict!
‘c’	00-7F	linux/coda.h	conflict!
‘c’	00-1F	linux/chio.h	conflict!
‘c’	80-9F	arch/s390/include/asm/chsc.h	conflict!
‘c’	A0-AF	arch/x86/include/asm/msr.h conflict!
‘d’	00-FF	linux/char/drm/drm.h	conflict!
‘d’	02-40	pcmcia/ds.h	conflict!
‘d’	F0-FF	linux/digi1.h
‘e’	all	linux/digi1.h	conflict!
‘f’	00-1F	linux/ext2_fs.h	conflict!
‘f’	00-1F	linux/ext3_fs.h	conflict!
‘f’	00-0F	fs/jfs/jfs_dinode.h	conflict!
‘f’	00-0F	fs/ext4/ext4.h	conflict!
‘f’	00-0F	linux/fs.h	conflict!
‘f’	00-0F	fs/ocfs2/ocfs2_fs.h	conflict!
‘f’	13-27	linux/fscrypt.h
‘f’	81-8F	linux/fsverity.h
‘g’	00-0F	linux/usb/gadgetfs.h
‘g’	20-2F	linux/usb/g_printer.h
‘h’	00-7F		conflict! Charon filesystem <mailto:zapman@interlan.net>
‘h’	00-1F	linux/hpet.h	conflict!
‘h’	80-8F	fs/hfsplus/ioctl.c
‘i’	00-3F	linux/i2o-dev.h	conflict!
‘i’	0B-1F	linux/ipmi.h	conflict!
‘i’	80-8F	linux/i8k.h
‘i’	90-9F	linux/iio/*.h	IIO
‘j’	00-3F	linux/joystick.h
‘k’	00-0F	linux/spi/spidev.h	conflict!
‘k’	00-05	video/kyro.h	conflict!
‘k’	10-17	linux/hsi/hsi_char.h	HSI character device
‘l’	00-3F	linux/tcfs_fs.h	transparent cryptographic file system <http://web.archive.org/web/%2A/http://mikonos.dia.unisa.it/tcfs>
‘l’	40-7F	linux/udf_fs_i.h	in development: <https://github.com/pali/udftools>
‘m’	00-09	linux/mmtimer.h	conflict!
‘m’	all	linux/mtio.h	conflict!
‘m’	all	linux/soundcard.h	conflict!
‘m’	00-19	drivers/message/fusion/mptctl.h	conflict!
‘m’	00	drivers/scsi/megaraid/megaraid_ioctl.h	conflict!
‘n’	00-7F	linux/ncp_fs.h and fs/ncpfs/ioctl.c
‘n’	80-8F	uapi/linux/nilfs2_api.h	NILFS2
‘n’	E0-FF	linux/matroxfb.h	matroxfb
‘o’	00-1F	fs/ocfs2/ocfs2_fs.h	OCFS2
‘o’	00-03	mtd/ubi-user.h	conflict! (OCFS2 and UBI overlaps)
‘o’	40-41	mtd/ubi-user.h	UBI
‘o’	01-A1	linux/dvb/*.h	DVB
‘p’	00-0F	linux/phantom.h	conflict! (OpenHaptics needs this)
‘p’	00-1F	linux/rtc.h	conflict!
‘p’	40-7F	linux/nvram.h
‘p’	80-9F	linux/ppdev.h	user-space parport <mailto:tim@cyberelk.net>
‘p’	A1-A5	linux/pps.h	LinuxPPS
‘p’	B1-B3	linux/pps_gen.h	LinuxPPS <mailto:giometti@linux.it>
‘q’	00-1F	linux/serio.h
‘q’	80-FF	linux/telephony.h linux/ixjuser.h	Internet PhoneJACK, Internet LineJACK <http://web.archive.org/web/%2A/http://www.quicknet.net>
‘r’	00-1F	linux/msdos_fs.h and fs/fat/dir.c
‘s’	all	linux/cdk.h
‘t’	00-7F	linux/ppp-ioctl.h
‘t’	80-8F	linux/isdn_ppp.h
‘t’	90-91	linux/toshiba.h	toshiba and toshiba_acpi SMM
‘u’	00-1F	linux/smb_fs.h	gone
‘u’	00-2F	linux/ublk_cmd.h	conflict!
‘u’	20-3F	linux/uvcvideo.h	USB video class host driver
‘u’	40-4f	linux/udmabuf.h	userspace dma-buf misc device
‘v’	00-1F	linux/ext2_fs.h	conflict!
‘v’	00-1F	linux/fs.h	conflict!
‘v’	00-0F	linux/sonypi.h	conflict!
‘v’	00-0F	media/v4l2-subdev.h	conflict!
‘v’	20-27	arch/powerpc/include/uapi/asm/vas-api.h	VAS API
‘v’	C0-FF	linux/meye.h	conflict!
‘w’	all		CERN SCI driver
‘y’	00-1F		packet based user level communications <mailto:zapman@interlan.net>
‘z’	00-3F		CAN bus card conflict! <mailto:hdstich@connectu.ulm.circular.de>
‘z’	40-7F		CAN bus card conflict! <mailto:oe@port.de>
‘z’	10-4F	drivers/s390/crypto/zcrypt_api.h	conflict!
‘|’	00-7F	linux/media.h
‘|’	80-9F	samples/	Any sample and example drivers
0x80	00-1F	linux/fb.h
0x81	00-1F	linux/vduse.h
0x89	00-06	arch/x86/include/asm/sockios.h
0x89	0B-DF	linux/sockios.h
0x89	E0-EF	linux/sockios.h	SIOCPROTOPRIVATE range
0x89	F0-FF	linux/sockios.h	SIOCDEVPRIVATE range
0x8A	00-1F	linux/eventpoll.h
0x8B	all	linux/wireless.h
0x8C	00-3F		WiNRADiO driver <http://www.winradio.com.au/>
0x90	00	drivers/cdrom/sbpcd.h
0x92	00-0F	drivers/usb/mon/mon_bin.c
0x93	60-7F	linux/auto_fs.h
0x94	all	fs/btrfs/ioctl.h and linux/fs.h	Btrfs filesystem some lifted to vfs/generic
0x97	00-7F	fs/ceph/ioctl.h	Ceph file system
0x99	00-0F		537-Addinboard driver <mailto:buk@buks.ipn.de>
0x9A	00-0F	include/uapi/fwctl/fwctl.h
0xA0	all	linux/sdp/sdp.h	Industrial Device Project <mailto:kenji@bitgate.com>
0xA1	0	linux/vtpm_proxy.h	TPM Emulator Proxy Driver
0xA2	all	uapi/linux/acrn.h	ACRN hypervisor
0xA3	80-8F		Port ACL in development: <mailto:tlewis@mindspring.com>
0xA4	00-1F	uapi/linux/tee.h	Generic TEE subsystem
0xA4	00-1F	uapi/asm/sgx.h	<mailto:linux-sgx@vger.kernel.org>
0xA5	01-05	linux/surface_aggregator/cdev.h	Microsoft Surface Platform System Aggregator <mailto:luzmaximilian@gmail.com>
0xA5	20-2F	linux/surface_aggregator/dtx.h	Microsoft Surface DTX driver <mailto:luzmaximilian@gmail.com>
0xA6	00-0F	uapi/linux/alloc_tag.h	Memory allocation profiling <mailto:surenb@google.com>
0xAA	00-3F	linux/uapi/linux/userfaultfd.h
0xAB	00-1F	linux/nbd.h
0xAC	00-1F	linux/raw.h
0xAD	00		Netfilter device in development: <mailto:rusty@rustcorp.com.au>
0xAE	00-1F	linux/kvm.h	Kernel-based Virtual Machine <mailto:kvm@vger.kernel.org>
0xAE	40-FF	linux/kvm.h	Kernel-based Virtual Machine <mailto:kvm@vger.kernel.org>
0xAE	20-3F	linux/nitro_enclaves.h	Nitro Enclaves
0xAF	00-1F	linux/fsl_hypervisor.h	Freescale hypervisor
0xB0	all		RATIO devices in development: <mailto:vgo@ratio.de>
0xB1	00-1F		PPPoX <mailto:mostrows@styx.uwaterloo.ca>
0xB2	00	arch/powerpc/include/uapi/asm/papr-vpd.h	powerpc/pseries VPD API <mailto:linuxppc-dev@lists.ozlabs.org>
0xB2	01-02	arch/powerpc/include/uapi/asm/papr-sysparm.h	powerpc/pseries system parameter API <mailto:linuxppc-dev@lists.ozlabs.org>
0xB2	03-05	arch/powerpc/include/uapi/asm/papr-indices.h	powerpc/pseries indices API <mailto:linuxppc-dev@lists.ozlabs.org>
0xB2	06-07	arch/powerpc/include/uapi/asm/papr-platform-dump.h	powerpc/pseries Platform Dump API <mailto:linuxppc-dev@lists.ozlabs.org>
0xB2	08	arch/powerpc/include/uapi/asm/papr-physical-attestation.h	powerpc/pseries Physical Attestation API <mailto:linuxppc-dev@lists.ozlabs.org>
0xB2	09	arch/powerpc/include/uapi/asm/papr-hvpipe.h	powerpc/pseries HVPIPE API <mailto:linuxppc-dev@lists.ozlabs.org>
0xB3	00	linux/mmc/ioctl.h
0xB4	00-0F	linux/gpio.h	<mailto:linux-gpio@vger.kernel.org>
0xB5	00-0F	uapi/linux/rpmsg.h	<mailto:linux-remoteproc@vger.kernel.org>
0xB6	all	linux/fpga-dfl.h
0xB7	all	uapi/linux/remoteproc_cdev.h	<mailto:linux-remoteproc@vger.kernel.org>
0xB7	all	uapi/linux/nsfs.h	<mailto:Andrei Vagin <avagin@openvz.org>>
0xB8	01-02	uapi/misc/mrvl_cn10k_dpi.h	Marvell CN10K DPI driver
0xB8	all	uapi/linux/mshv.h	Microsoft Hyper-V /dev/mshv driver <mailto:linux-hyperv@vger.kernel.org>
0xBA	00-0F	uapi/linux/liveupdate.h	Pasha Tatashin <mailto:pasha.tatashin@soleen.com>
0xC0	00-0F	linux/usb/iowarrior.h
0xCA	00-0F	uapi/misc/cxl.h	Dead since 6.15
0xCA	10-2F	uapi/misc/ocxl.h
0xCA	80-BF	uapi/scsi/cxlflash_ioctl.h	Dead since 6.15
0xCB	00-1F		CBM serial IEC bus in development: <mailto:michael.klein@puffin.lb.shuttle.de>
0xCC	00-0F	drivers/misc/ibmvmc.h	pseries VMC driver
0xCD	01	linux/reiserfs_fs.h	Dead since 6.13
0xCE	01-02	uapi/linux/cxl_mem.h	Compute Express Link Memory Devices
0xCF	02	fs/smb/client/cifs_ioctl.h
0xDD	00-3F		ZFCP device driver see drivers/s390/scsi/ <mailto:aherrman@de.ibm.com>
0xE5	00-3F	linux/fuse.h
0xEC	00-01	drivers/platform/chrome/cros_ec_dev.h	ChromeOS EC driver
0xEE	00-09	uapi/linux/pfrut.h	Platform Firmware Runtime Update and Telemetry
0xF3	00-3F	drivers/usb/misc/sisusbvga/sisusb.h	sisfb (in development) <mailto:thomas@winischhofer.net>
0xF6	all		LTTng Linux Trace Toolkit Next Generation <mailto:mathieu.desnoyers@efficios.com>
0xF8	all	arch/x86/include/uapi/asm/amd_hsmp.h	AMD HSMP EPYC system management interface driver <mailto:nchatrad@amd.com>
0xF9	00-0F	uapi/misc/amd-apml.h	AMD side band system management interface driver <mailto:naveenkrishna.chatradhi@amd.com>
0xFD	all	linux/dm-ioctl.h
0xFE	all	linux/isst_if.h