path: root/Documentation/magic-number.txt
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authorMauro Carvalho Chehab <>2016-09-21 08:40:21 -0300
committerMauro Carvalho Chehab <>2016-10-24 08:12:35 -0200
commit186128f75392f8478ad1b32a675627d738881ca4 (patch)
treec72c5e91c636e58ae0a9496fb2759074f484244f /Documentation/magic-number.txt
parent0e4f07a65f53e7b3afab71925e56fe6aaa07d696 (diff)
docs-rst: add documents to development-process
Add several documents to the development-process ReST book. As we don't want renames, use symlinks instead, keeping those documents on their original place. Acked-by: Greg Kroah-Hartman <> Signed-off-by: Mauro Carvalho Chehab <>
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-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 then 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.
- Theodore Ts'o
- 31 Mar 94
- The magic table is current to Linux 2.1.55.
- Michael Chastain
- <>
- 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:>
- 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
- <>
- 03 Nov 2002
- Updated the magic table to Linux 2.5.74.
- Fabian Frederick
- <>
- 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.
-IrDA subsystem also uses large number of own magic numbers, see
-``include/net/irda/irda.h`` for a complete list of them.
-HFS is another larger user of magic numbers - you can find them in