Documentation/magic-number.txt

   1 This file is a registry of magic numbers which are in use.  When you
   2 add a magic number to a structure, you should also add it to this
   3 file, since it is best if the magic numbers used by various structures
   4 are unique.
   5
   6 It is a *very* good idea to protect kernel data structures with magic
   7 numbers.  This allows you to check at run time whether (a) a structure
   8 has been clobbered, or (b) you've passed the wrong structure to a
   9 routine.  This last is especially useful --- particularly when you are
  10 passing pointers to structures via a void * pointer.  The tty code,
  11 for example, does this frequently to pass driver-specific and line
  12 discipline-specific structures back and forth.
  13
  14 The way to use magic numbers is to declare then at the beginning of
  15 the structure, like so:
  16
  17 struct tty_ldisc {
  18         int     magic;
  19         ...
  20 };
  21
  22 Please follow this discipline when you are adding future enhancements
  23 to the kernel!  It has saved me countless hours of debugging,
  24 especially in the screwy cases where an array has been overrun and
  25 structures following the array have been overwritten.  Using this
  26 discipline, these cases get detected quickly and safely.
  27
  28                                         Theodore Ts'o
  29                                         31 Mar 94
  30
  31 The magic table is current to Linux 2.1.55.
  32
  33                                         Michael Chastain
  34                                         <mailto:mec@shout.net>
  35                                         22 Sep 1997
  36
  37 Now it should be up to date with Linux 2.1.112. Because
  38 we are in feature freeze time it is very unlikely that
  39 something will change before 2.2.x. The entries are
  40 sorted by number field.
  41
  42                                         Krzysztof G. Baranowski
  43                                         <mailto: kgb@knm.org.pl>
  44                                         29 Jul 1998
  45
  46 Magic Name            Number      Structure            File
  47 ===========================================================================
  48 PG_MAGIC              'P'         pg_{read,write}_hdr include/linux/pg.h
  49 MKISS_DRIVER_MAGIC    0x04bf      mkiss_channel     drivers/net/mkiss.h
  50 RISCOM8_MAGIC         0x0907      riscom_port       drivers/char/riscom8.h
  51 APM_BIOS_MAGIC        0x4101      apm_bios_struct   include/linux/apm_bios.h
  52 CYCLADES_MAGIC        0x4359      cyclades_port     include/linux/cyclades.h
  53 FASYNC_MAGIC          0x4601      fasync_struct     include/linux/fs.h
  54 PTY_MAGIC             0x5001      (none at the moment)
  55                                                     drivers/char/pty.c
  56 PPP_MAGIC             0x5002      ppp               include/linux/if_ppp.h
  57 SERIAL_MAGIC          0x5301      async_struct      include/linux/serial.h
  58 SSTATE_MAGIC          0x5302      serial_state      include/linux/serial.h
  59 SLIP_MAGIC            0x5302      slip              drivers/net/slip.h
  60 STRIP_MAGIC           0x5303      strip             drivers/net/strip.c
  61 X25_ASY_MAGIC         0x5303      x25_asy           drivers/net/x25_asy.h
  62 SIXPACK_MAGIC         0x5304      sixpack           drivers/net/hamradio/6pack.h
  63 AX25_MAGIC            0x5316      ax_disp           drivers/net/mkiss.h
  64 ESP_MAGIC             0x53ee      esp_struct        drivers/char/esp.h
  65 TTY_MAGIC             0x5401      tty_struct        include/linux/tty.h
  66 TTY_DRIVER_MAGIC      0x5402      tty_driver        include/linux/tty_driver.h
  67 TTY_LDISC_MAGIC       0x5403      tty_ldisc         include/linux/tty_ldisc.h
  68 SCC_MAGIC             0x8530      scc_channel       include/linux/scc.h
  69 SPECIALIX_MAGIC       0x0907      specialix_port    drivers/char/specialix_io8.h
  70 CG_MAGIC              0x090255    ufs_cylinder_group include/linux/ufs_fs.h
  71 RPORT_MAGIC           0x525001    r_port            drivers/char/rocket_int.h
  72 GDTIOCTL_MAGIC        0x06030f07  gdth_iowr_str     drivers/scsi/gdth_ioctl.h
  73 NBD_REQUEST_MAGIC     0x12560953  nbd_request       include/linux/nbd.h
  74 SLAB_RED_MAGIC2       0x170fc2a5  (any)             mm/slab.c
  75 BAYCOM_MAGIC          0x19730510  baycom_state      drivers/net/baycom_epp.c
  76 ISDN_X25IFACE_MAGIC   0x1e75a2b9  isdn_x25iface_proto_data
  77                                                     drivers/isdn/isdn_x25iface.h
  78 ECP_MAGIC             0x21504345  cdkecpsig         include/linux/cdk.h
  79 LSMAGIC               0x2a3b4d2a  ls                drivers/fc4/fc.c
  80 LSOMAGIC              0x2a3c4e3c  lso               drivers/fc4/fc.c
  81 WANPIPE_MAGIC         0x414C4453  sdla_{dump,exec}  include/linux/wanpipe.h
  82 CODA_CNODE_MAGIC      0x47114711  coda_inode_info   include/linux/coda_fs_i.h
  83 ISDN_ASYNC_MAGIC      0x49344C01  modem_info        include/linux/isdn.h
  84 ISDN_NET_MAGIC        0x49344C02  isdn_net_local_s  include/linux/isdn.h
  85 STLI_BOARDMAGIC       0x4bc6c825  stlibrd           include/linux/istallion.h
  86 SLAB_C_MAGIC          0x4f17a36d  kmem_cache_s      mm/slab.c
  87 ROUTER_MAGIC          0x524d4157  wan_device        include/linux/wanrouter.h
  88 SLAB_RED_MAGIC1       0x5a2cf071  (any)             mm/slab.c
  89 STL_PORTMAGIC         0x5a7182c9  stlport           include/linux/stallion.h
  90 HDLCDRV_MAGIC         0x5ac6e778  hdlcdrv_state     include/linux/hdlcdrv.h
  91 EPCA_MAGIC            0x5c6df104  channel           include/linux/epca.h
  92 PCXX_MAGIC            0x5c6df104  channel           drivers/char/pcxx.h
  93 LO_MAGIC              0x68797548  nbd_device        include/linux/nbd.h
  94 STL_PANELMAGIC        0x7ef621a1  stlpanel          include/linux/stallion.h
  95 NBD_REPLY_MAGIC       0x96744668  nbd_reply         include/linux/nbd.h
  96 STL_BOARDMAGIC        0xa2267f52  stlbrd            include/linux/stallion.h
  97 SLAB_MAGIC_ALLOC      0xa5c32f2b  kmem_slab_s       mm/slab.c
  98 SLAB_MAGIC_DESTROYED  0xb2f23c5a  kmem_slab_s       mm/slab.c
  99 STLI_PORTMAGIC        0xe671c7a1  stliport          include/linux/istallion.h
 100 CCB_MAGIC             0xf2691ad2  ccb               drivers/scsi/ncr53c8xx.c