Ioctl Numbers

19 October 1999

Michael Elizabeth Chastain <>

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

_IO an ioctl with no parameters
_IOW an ioctl with write parameters (copy_from_user)
_IOR an ioctl with read parameters (copy_to_user)
_IOWR an ioctl with both write and read parameters.

‘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 _IO, _IOW, _IOR, or _IOWR 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. You can register the block by patching this file and submitting the patch to Linus Torvalds. Or you can e-mail me at <> and I’ll register one for you.

The second argument to _IO, _IOW, _IOR, or _IOWR is a sequence number to distinguish ioctls from each other. The third argument to _IOW, _IOR, or _IOWR 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 _IO, _IOW, _IOR, or _IOWR.
  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 user land for Linux/x86. It contains most drivers up to 2.6.31, but I know I am missing some. There has been no attempt to list non-X86 architectures or ioctls 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  
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  
0x1b all   InfiniBand Subsystem <>
0x20 all drivers/cdrom/cm206.h  
0x22 all scsi/sg.h  
‘!’ 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 <>
‘&’ 00-07 drivers/firewire/nosy-user.h  
‘1’ 00-1F linux/timepps.h PPS kit from Ulrich Windl <>
‘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 <>
‘;’ 64-7F linux/vfio.h  
‘@’ 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 <>
‘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  
‘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 drivers/video/intelfb/intelfb.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!
‘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 <>
‘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!
‘J’ 00-1F drivers/scsi/gdth_ioctl.h  
‘K’ all linux/kd.h  
‘L’ 00-1F linux/loop.h conflict!
‘L’ 10-1F drivers/scsi/mpt3sas/mpt3sas_ctl.h conflict!
‘L’ 20-2F linux/lightnvm.h  
‘L’ E0-FF linux/ppdd.h encrypted disk device driver <>
‘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  
‘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!
‘Q’ all linux/soundcard.h  
‘R’ 00-1F linux/random.h conflict!
‘R’ 01 linux/rfkill.h conflict!
‘R’ C0-DF net/bluetooth/rfcomm.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/davinci/vpfe_capture.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!
‘X’ 01 linux/pktcdvd.h conflict!
‘Y’ all linux/cyclades.h  
‘Z’ 14-15 drivers/message/fusion/mptctl.h  
‘[‘ 00-3F linux/usb/tmc.h USB Test and Measurement Devices <>
‘a’ all linux/atm*.h, linux/sonet.h ATM on linux <>
‘a’ 00-0F drivers/crypto/qat/qat_common/adf_cfg_common.h conflict! qat driver
‘b’ 00-FF   conflict! bit3 vme host bridge <>
‘c’ all linux/cm4000_cs.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 <>
‘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  
‘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 <>
‘l’ 40-7F linux/udf_fs_i.h in development: <>
‘m’ 00-09 linux/mmtimer.h conflict!
‘m’ all linux/mtio.h conflict!
‘m’ all linux/soundcard.h conflict!
‘m’ all linux/synclink.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 <>
‘p’ A1-A5 linux/pps.h LinuxPPS <>
‘q’ 00-1F linux/serio.h  
‘q’ 80-FF linux/telephony.h linux/ixjuser.h Internet PhoneJACK, Internet LineJACK <>
‘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’ 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 <>
‘z’ 00-3F   CAN bus card conflict! <>
‘z’ 40-7F   CAN bus card conflict! <>
‘z’ 10-4F drivers/s390/crypto/zcrypt_api.h conflict!
‘|’ 00-7F linux/media.h  
0x80 00-1F linux/fb.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 E0-EF linux/dn.h PROTOPRIVATE range
0x89 F0-FF linux/sockios.h SIOCDEVPRIVATE range
0x8B all linux/wireless.h  
0x8C 00-3F   WiNRADiO driver <>
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 <>
0xA0 all linux/sdp/sdp.h Industrial Device Project <>
0xA1 0 linux/vtpm_proxy.h TPM Emulator Proxy Driver
0xA3 80-8F   Port ACL in development: <>
0xA3 90-9F linux/dtlk.h  
0xA4 00-1F uapi/linux/tee.h Generic TEE subsystem
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: <>
0xAE 00-1F linux/kvm.h Kernel-based Virtual Machine <>
0xAE 40-FF linux/kvm.h Kernel-based Virtual Machine <>
0xAE 20-3F linux/nitro_enclaves.h Nitro Enclaves
0xAF 00-1F linux/fsl_hypervisor.h Freescale hypervisor
0xB0 all   RATIO devices in development: <>
0xB1 00-1F   PPPoX <>
0xB3 00 linux/mmc/ioctl.h  
0xB4 00-0F linux/gpio.h <>
0xB5 00-0F uapi/linux/rpmsg.h <>
0xB6 all linux/fpga-dfl.h  
0xB7 all uapi/linux/remoteproc_cdev.h <>
0xC0 00-0F linux/usb/iowarrior.h  
0xCA 00-0F uapi/misc/cxl.h  
0xCA 10-2F uapi/misc/ocxl.h  
0xCA 80-BF uapi/scsi/cxlflash_ioctl.h  
0xCB 00-1F   CBM serial IEC bus in development: <>
0xCC 00-0F drivers/misc/ibmvmc.h pseries VMC driver
0xCD 01 linux/reiserfs_fs.h  
0xCF 02 fs/cifs/ioctl.c  
0xDB 00-0F drivers/char/mwave/mwavepub.h  
0xDD 00-3F   ZFCP device driver see drivers/s390/scsi/ <>
0xE5 00-3F linux/fuse.h  
0xEC 00-01 drivers/platform/chrome/cros_ec_dev.h ChromeOS EC driver
0xF3 00-3F drivers/usb/misc/sisusbvga/sisusb.h sisfb (in development) <>
0xF6 all   LTTng Linux Trace Toolkit Next Generation <>
0xFD all linux/dm-ioctl.h  
0xFE all linux/isst_if.h