1.. _magicnumbers: 2 3Linux magic numbers 4=================== 5 6This file is a registry of magic numbers which are in use. When you 7add a magic number to a structure, you should also add it to this 8file, since it is best if the magic numbers used by various structures 9are unique. 10 11It is a **very** good idea to protect kernel data structures with magic 12numbers. This allows you to check at run time whether (a) a structure 13has been clobbered, or (b) you've passed the wrong structure to a 14routine. This last is especially useful --- particularly when you are 15passing pointers to structures via a void * pointer. The tty code, 16for example, does this frequently to pass driver-specific and line 17discipline-specific structures back and forth. 18 19The way to use magic numbers is to declare them at the beginning of 20the structure, like so:: 21 22 struct tty_ldisc { 23 int magic; 24 ... 25 }; 26 27Please follow this discipline when you are adding future enhancements 28to the kernel! It has saved me countless hours of debugging, 29especially in the screwy cases where an array has been overrun and 30structures following the array have been overwritten. Using this 31discipline, these cases get detected quickly and safely. 32 33Changelog:: 34 35 Theodore Ts'o 36 31 Mar 94 37 38 The magic table is current to Linux 2.1.55. 39 40 Michael Chastain 41 <mailto:mec@shout.net> 42 22 Sep 1997 43 44 Now it should be up to date with Linux 2.1.112. Because 45 we are in feature freeze time it is very unlikely that 46 something will change before 2.2.x. The entries are 47 sorted by number field. 48 49 Krzysztof G. Baranowski 50 <mailto: kgb@knm.org.pl> 51 29 Jul 1998 52 53 Updated the magic table to Linux 2.5.45. Right over the feature freeze, 54 but it is possible that some new magic numbers will sneak into the 55 kernel before 2.6.x yet. 56 57 Petr Baudis 58 <pasky@ucw.cz> 59 03 Nov 2002 60 61 Updated the magic table to Linux 2.5.74. 62 63 Fabian Frederick 64 <ffrederick@users.sourceforge.net> 65 09 Jul 2003 66 67 68===================== ================ ======================== ========================================== 69Magic Name Number Structure File 70===================== ================ ======================== ========================================== 71PG_MAGIC 'P' pg_{read,write}_hdr ``include/linux/pg.h`` 72CMAGIC 0x0111 user ``include/linux/a.out.h`` 73MKISS_DRIVER_MAGIC 0x04bf mkiss_channel ``drivers/net/mkiss.h`` 74HDLC_MAGIC 0x239e n_hdlc ``drivers/char/n_hdlc.c`` 75APM_BIOS_MAGIC 0x4101 apm_user ``arch/x86/kernel/apm_32.c`` 76CYCLADES_MAGIC 0x4359 cyclades_port ``include/linux/cyclades.h`` 77DB_MAGIC 0x4442 fc_info ``drivers/net/iph5526_novram.c`` 78DL_MAGIC 0x444d fc_info ``drivers/net/iph5526_novram.c`` 79FASYNC_MAGIC 0x4601 fasync_struct ``include/linux/fs.h`` 80FF_MAGIC 0x4646 fc_info ``drivers/net/iph5526_novram.c`` 81ISICOM_MAGIC 0x4d54 isi_port ``include/linux/isicom.h`` 82PTY_MAGIC 0x5001 ``drivers/char/pty.c`` 83PPP_MAGIC 0x5002 ppp ``include/linux/if_pppvar.h`` 84SERIAL_MAGIC 0x5301 async_struct ``include/linux/serial.h`` 85SSTATE_MAGIC 0x5302 serial_state ``include/linux/serial.h`` 86SLIP_MAGIC 0x5302 slip ``drivers/net/slip.h`` 87STRIP_MAGIC 0x5303 strip ``drivers/net/strip.c`` 88X25_ASY_MAGIC 0x5303 x25_asy ``drivers/net/x25_asy.h`` 89SIXPACK_MAGIC 0x5304 sixpack ``drivers/net/hamradio/6pack.h`` 90AX25_MAGIC 0x5316 ax_disp ``drivers/net/mkiss.h`` 91TTY_MAGIC 0x5401 tty_struct ``include/linux/tty.h`` 92MGSL_MAGIC 0x5401 mgsl_info ``drivers/char/synclink.c`` 93TTY_DRIVER_MAGIC 0x5402 tty_driver ``include/linux/tty_driver.h`` 94MGSLPC_MAGIC 0x5402 mgslpc_info ``drivers/char/pcmcia/synclink_cs.c`` 95TTY_LDISC_MAGIC 0x5403 tty_ldisc ``include/linux/tty_ldisc.h`` 96USB_SERIAL_MAGIC 0x6702 usb_serial ``drivers/usb/serial/usb-serial.h`` 97FULL_DUPLEX_MAGIC 0x6969 ``drivers/net/ethernet/dec/tulip/de2104x.c`` 98USB_BLUETOOTH_MAGIC 0x6d02 usb_bluetooth ``drivers/usb/class/bluetty.c`` 99RFCOMM_TTY_MAGIC 0x6d02 ``net/bluetooth/rfcomm/tty.c`` 100USB_SERIAL_PORT_MAGIC 0x7301 usb_serial_port ``drivers/usb/serial/usb-serial.h`` 101CG_MAGIC 0x00090255 ufs_cylinder_group ``include/linux/ufs_fs.h`` 102RPORT_MAGIC 0x00525001 r_port ``drivers/char/rocket_int.h`` 103LSEMAGIC 0x05091998 lse ``drivers/fc4/fc.c`` 104GDTIOCTL_MAGIC 0x06030f07 gdth_iowr_str ``drivers/scsi/gdth_ioctl.h`` 105RIEBL_MAGIC 0x09051990 ``drivers/net/atarilance.c`` 106NBD_REQUEST_MAGIC 0x12560953 nbd_request ``include/linux/nbd.h`` 107RED_MAGIC2 0x170fc2a5 (any) ``mm/slab.c`` 108BAYCOM_MAGIC 0x19730510 baycom_state ``drivers/net/baycom_epp.c`` 109ISDN_X25IFACE_MAGIC 0x1e75a2b9 isdn_x25iface_proto_data ``drivers/isdn/isdn_x25iface.h`` 110ECP_MAGIC 0x21504345 cdkecpsig ``include/linux/cdk.h`` 111LSOMAGIC 0x27091997 lso ``drivers/fc4/fc.c`` 112LSMAGIC 0x2a3b4d2a ls ``drivers/fc4/fc.c`` 113WANPIPE_MAGIC 0x414C4453 sdla_{dump,exec} ``include/linux/wanpipe.h`` 114CS_CARD_MAGIC 0x43525553 cs_card ``sound/oss/cs46xx.c`` 115LABELCL_MAGIC 0x4857434c labelcl_info_s ``include/asm/ia64/sn/labelcl.h`` 116ISDN_ASYNC_MAGIC 0x49344C01 modem_info ``include/linux/isdn.h`` 117CTC_ASYNC_MAGIC 0x49344C01 ctc_tty_info ``drivers/s390/net/ctctty.c`` 118ISDN_NET_MAGIC 0x49344C02 isdn_net_local_s ``drivers/isdn/i4l/isdn_net_lib.h`` 119SAVEKMSG_MAGIC2 0x4B4D5347 savekmsg ``arch/*/amiga/config.c`` 120CS_STATE_MAGIC 0x4c4f4749 cs_state ``sound/oss/cs46xx.c`` 121SLAB_C_MAGIC 0x4f17a36d kmem_cache ``mm/slab.c`` 122COW_MAGIC 0x4f4f4f4d cow_header_v1 ``arch/um/drivers/ubd_user.c`` 123I810_CARD_MAGIC 0x5072696E i810_card ``sound/oss/i810_audio.c`` 124TRIDENT_CARD_MAGIC 0x5072696E trident_card ``sound/oss/trident.c`` 125ROUTER_MAGIC 0x524d4157 wan_device [in ``wanrouter.h`` pre 3.9] 126SAVEKMSG_MAGIC1 0x53415645 savekmsg ``arch/*/amiga/config.c`` 127GDA_MAGIC 0x58464552 gda ``arch/mips/include/asm/sn/gda.h`` 128RED_MAGIC1 0x5a2cf071 (any) ``mm/slab.c`` 129EEPROM_MAGIC_VALUE 0x5ab478d2 lanai_dev ``drivers/atm/lanai.c`` 130HDLCDRV_MAGIC 0x5ac6e778 hdlcdrv_state ``include/linux/hdlcdrv.h`` 131PCXX_MAGIC 0x5c6df104 channel ``drivers/char/pcxx.h`` 132KV_MAGIC 0x5f4b565f kernel_vars_s ``arch/mips/include/asm/sn/klkernvars.h`` 133I810_STATE_MAGIC 0x63657373 i810_state ``sound/oss/i810_audio.c`` 134TRIDENT_STATE_MAGIC 0x63657373 trient_state ``sound/oss/trident.c`` 135M3_CARD_MAGIC 0x646e6f50 m3_card ``sound/oss/maestro3.c`` 136FW_HEADER_MAGIC 0x65726F66 fw_header ``drivers/atm/fore200e.h`` 137SLOT_MAGIC 0x67267321 slot ``drivers/hotplug/cpqphp.h`` 138SLOT_MAGIC 0x67267322 slot ``drivers/hotplug/acpiphp.h`` 139LO_MAGIC 0x68797548 nbd_device ``include/linux/nbd.h`` 140OPROFILE_MAGIC 0x6f70726f super_block ``drivers/oprofile/oprofilefs.h`` 141M3_STATE_MAGIC 0x734d724d m3_state ``sound/oss/maestro3.c`` 142VMALLOC_MAGIC 0x87654320 snd_alloc_track ``sound/core/memory.c`` 143KMALLOC_MAGIC 0x87654321 snd_alloc_track ``sound/core/memory.c`` 144PWC_MAGIC 0x89DC10AB pwc_device ``drivers/usb/media/pwc.h`` 145NBD_REPLY_MAGIC 0x96744668 nbd_reply ``include/linux/nbd.h`` 146ENI155_MAGIC 0xa54b872d midway_eprom ``drivers/atm/eni.h`` 147CODA_MAGIC 0xC0DAC0DA coda_file_info ``fs/coda/coda_fs_i.h`` 148DPMEM_MAGIC 0xc0ffee11 gdt_pci_sram ``drivers/scsi/gdth.h`` 149YAM_MAGIC 0xF10A7654 yam_port ``drivers/net/hamradio/yam.c`` 150CCB_MAGIC 0xf2691ad2 ccb ``drivers/scsi/ncr53c8xx.c`` 151QUEUE_MAGIC_FREE 0xf7e1c9a3 queue_entry ``drivers/scsi/arm/queue.c`` 152QUEUE_MAGIC_USED 0xf7e1cc33 queue_entry ``drivers/scsi/arm/queue.c`` 153HTB_CMAGIC 0xFEFAFEF1 htb_class ``net/sched/sch_htb.c`` 154NMI_MAGIC 0x48414d4d455201 nmi_s ``arch/mips/include/asm/sn/nmi.h`` 155===================== ================ ======================== ========================================== 156 157Note that there are also defined special per-driver magic numbers in sound 158memory management. See ``include/sound/sndmagic.h`` for complete list of them. Many 159OSS sound drivers have their magic numbers constructed from the soundcard PCI 160ID - these are not listed here as well. 161 162HFS is another larger user of magic numbers - you can find them in 163``fs/hfs/hfs.h``. 164