Linux magic numbers

This file is a registry of magic numbers which are in use. When you add a magic number to a structure, you should also add it to this file, since it is best if the magic numbers used by various structures are unique.

It is a very good idea to protect kernel data structures with magic numbers. This allows you to check at run time whether (a) a structure has been clobbered, or (b) you’ve passed the wrong structure to a routine. This last is especially useful — particularly when you are passing pointers to structures via a void * pointer. The tty code, for example, does this frequently to pass driver-specific and line discipline-specific structures back and forth.

The way to use magic numbers is to declare them at the beginning of the structure, like so:

struct tty_ldisc {
        int     magic;
        ...
};

Please follow this discipline when you are adding future enhancements to the kernel! It has saved me countless hours of debugging, especially in the screwy cases where an array has been overrun and structures following the array have been overwritten. Using this discipline, these cases get detected quickly and safely.

Changelog:

                                      Theodore Ts'o
                                      31 Mar 94

The magic table is current to Linux 2.1.55.

                                      Michael Chastain
                                      <mailto:mec@shout.net>
                                      22 Sep 1997

Now it should be up to date with Linux 2.1.112. Because
we are in feature freeze time it is very unlikely that
something will change before 2.2.x. The entries are
sorted by number field.

                                      Krzysztof G. Baranowski
                                      <mailto: kgb@knm.org.pl>
                                      29 Jul 1998

Updated the magic table to Linux 2.5.45. Right over the feature freeze,
but it is possible that some new magic numbers will sneak into the
kernel before 2.6.x yet.

                                      Petr Baudis
                                      <pasky@ucw.cz>
                                      03 Nov 2002

Updated the magic table to Linux 2.5.74.

                                      Fabian Frederick
                                      <ffrederick@users.sourceforge.net>
                                      09 Jul 2003

Magic Name

Number

Structure

File

PG_MAGIC

‘P’

pg_{read,write}_hdr

include/linux/pg.h

CMAGIC

0x0111

user

include/linux/a.out.h

MKISS_DRIVER_MAGIC

0x04bf

mkiss_channel

drivers/net/mkiss.h

HDLC_MAGIC

0x239e

n_hdlc

drivers/char/n_hdlc.c

APM_BIOS_MAGIC

0x4101

apm_user

arch/x86/kernel/apm_32.c

CYCLADES_MAGIC

0x4359

cyclades_port

include/linux/cyclades.h

DB_MAGIC

0x4442

fc_info

drivers/net/iph5526_novram.c

DL_MAGIC

0x444d

fc_info

drivers/net/iph5526_novram.c

FASYNC_MAGIC

0x4601

fasync_struct

include/linux/fs.h

FF_MAGIC

0x4646

fc_info

drivers/net/iph5526_novram.c

ISICOM_MAGIC

0x4d54

isi_port

include/linux/isicom.h

PTY_MAGIC

0x5001

drivers/char/pty.c

PPP_MAGIC

0x5002

ppp

include/linux/if_pppvar.h

SSTATE_MAGIC

0x5302

serial_state

include/linux/serial.h

SLIP_MAGIC

0x5302

slip

drivers/net/slip.h

STRIP_MAGIC

0x5303

strip

drivers/net/strip.c

SIXPACK_MAGIC

0x5304

sixpack

drivers/net/hamradio/6pack.h

AX25_MAGIC

0x5316

ax_disp

drivers/net/mkiss.h

TTY_MAGIC

0x5401

tty_struct

include/linux/tty.h

MGSL_MAGIC

0x5401

mgsl_info

drivers/char/synclink.c

TTY_DRIVER_MAGIC

0x5402

tty_driver

include/linux/tty_driver.h

MGSLPC_MAGIC

0x5402

mgslpc_info

drivers/char/pcmcia/synclink_cs.c

TTY_LDISC_MAGIC

0x5403

tty_ldisc

include/linux/tty_ldisc.h

USB_SERIAL_MAGIC

0x6702

usb_serial

drivers/usb/serial/usb-serial.h

FULL_DUPLEX_MAGIC

0x6969

drivers/net/ethernet/dec/tulip/de2104x.c

USB_BLUETOOTH_MAGIC

0x6d02

usb_bluetooth

drivers/usb/class/bluetty.c

RFCOMM_TTY_MAGIC

0x6d02

net/bluetooth/rfcomm/tty.c

USB_SERIAL_PORT_MAGIC

0x7301

usb_serial_port

drivers/usb/serial/usb-serial.h

CG_MAGIC

0x00090255

ufs_cylinder_group

include/linux/ufs_fs.h

RPORT_MAGIC

0x00525001

r_port

drivers/char/rocket_int.h

LSEMAGIC

0x05091998

lse

drivers/fc4/fc.c

GDTIOCTL_MAGIC

0x06030f07

gdth_iowr_str

drivers/scsi/gdth_ioctl.h

RIEBL_MAGIC

0x09051990

drivers/net/atarilance.c

NBD_REQUEST_MAGIC

0x12560953

nbd_request

include/linux/nbd.h

RED_MAGIC2

0x170fc2a5

(any)

mm/slab.c

BAYCOM_MAGIC

0x19730510

baycom_state

drivers/net/baycom_epp.c

ISDN_X25IFACE_MAGIC

0x1e75a2b9

isdn_x25iface_proto_data

drivers/isdn/isdn_x25iface.h

ECP_MAGIC

0x21504345

cdkecpsig

include/linux/cdk.h

LSOMAGIC

0x27091997

lso

drivers/fc4/fc.c

LSMAGIC

0x2a3b4d2a

ls

drivers/fc4/fc.c

WANPIPE_MAGIC

0x414C4453

sdla_{dump,exec}

include/linux/wanpipe.h

CS_CARD_MAGIC

0x43525553

cs_card

sound/oss/cs46xx.c

LABELCL_MAGIC

0x4857434c

labelcl_info_s

include/asm/ia64/sn/labelcl.h

ISDN_ASYNC_MAGIC

0x49344C01

modem_info

include/linux/isdn.h

CTC_ASYNC_MAGIC

0x49344C01

ctc_tty_info

drivers/s390/net/ctctty.c

ISDN_NET_MAGIC

0x49344C02

isdn_net_local_s

drivers/isdn/i4l/isdn_net_lib.h

SAVEKMSG_MAGIC2

0x4B4D5347

savekmsg

arch/*/amiga/config.c

CS_STATE_MAGIC

0x4c4f4749

cs_state

sound/oss/cs46xx.c

SLAB_C_MAGIC

0x4f17a36d

kmem_cache

mm/slab.c

COW_MAGIC

0x4f4f4f4d

cow_header_v1

arch/um/drivers/ubd_user.c

I810_CARD_MAGIC

0x5072696E

i810_card

sound/oss/i810_audio.c

TRIDENT_CARD_MAGIC

0x5072696E

trident_card

sound/oss/trident.c

ROUTER_MAGIC

0x524d4157

wan_device

[in wanrouter.h pre 3.9]

SAVEKMSG_MAGIC1

0x53415645

savekmsg

arch/*/amiga/config.c

GDA_MAGIC

0x58464552

gda

arch/mips/include/asm/sn/gda.h

RED_MAGIC1

0x5a2cf071

(any)

mm/slab.c

EEPROM_MAGIC_VALUE

0x5ab478d2

lanai_dev

drivers/atm/lanai.c

HDLCDRV_MAGIC

0x5ac6e778

hdlcdrv_state

include/linux/hdlcdrv.h

PCXX_MAGIC

0x5c6df104

channel

drivers/char/pcxx.h

KV_MAGIC

0x5f4b565f

kernel_vars_s

arch/mips/include/asm/sn/klkernvars.h

I810_STATE_MAGIC

0x63657373

i810_state

sound/oss/i810_audio.c

TRIDENT_STATE_MAGIC

0x63657373

trient_state

sound/oss/trident.c

M3_CARD_MAGIC

0x646e6f50

m3_card

sound/oss/maestro3.c

FW_HEADER_MAGIC

0x65726F66

fw_header

drivers/atm/fore200e.h

SLOT_MAGIC

0x67267321

slot

drivers/hotplug/cpqphp.h

SLOT_MAGIC

0x67267322

slot

drivers/hotplug/acpiphp.h

LO_MAGIC

0x68797548

nbd_device

include/linux/nbd.h

OPROFILE_MAGIC

0x6f70726f

super_block

drivers/oprofile/oprofilefs.h

M3_STATE_MAGIC

0x734d724d

m3_state

sound/oss/maestro3.c

VMALLOC_MAGIC

0x87654320

snd_alloc_track

sound/core/memory.c

KMALLOC_MAGIC

0x87654321

snd_alloc_track

sound/core/memory.c

PWC_MAGIC

0x89DC10AB

pwc_device

drivers/usb/media/pwc.h

NBD_REPLY_MAGIC

0x96744668

nbd_reply

include/linux/nbd.h

ENI155_MAGIC

0xa54b872d

midway_eprom

drivers/atm/eni.h

CODA_MAGIC

0xC0DAC0DA

coda_file_info

fs/coda/coda_fs_i.h

DPMEM_MAGIC

0xc0ffee11

gdt_pci_sram

drivers/scsi/gdth.h

YAM_MAGIC

0xF10A7654

yam_port

drivers/net/hamradio/yam.c

CCB_MAGIC

0xf2691ad2

ccb

drivers/scsi/ncr53c8xx.c

QUEUE_MAGIC_FREE

0xf7e1c9a3

queue_entry

drivers/scsi/arm/queue.c

QUEUE_MAGIC_USED

0xf7e1cc33

queue_entry

drivers/scsi/arm/queue.c

HTB_CMAGIC

0xFEFAFEF1

htb_class

net/sched/sch_htb.c

NMI_MAGIC

0x48414d4d455201

nmi_s

arch/mips/include/asm/sn/nmi.h

Note that there are also defined special per-driver magic numbers in sound memory management. See include/sound/sndmagic.h for complete list of them. Many OSS sound drivers have their magic numbers constructed from the soundcard PCI ID - these are not listed here as well.

HFS is another larger user of magic numbers - you can find them in fs/hfs/hfs.h.