.. _magicnumbers:
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``
SERIAL_MAGIC 0x5301 async_struct ``include/linux/serial.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``
X25_ASY_MAGIC 0x5303 x25_asy ``drivers/net/x25_asy.h``
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``.