xref: /openbmc/linux/Documentation/process/magic-number.rst (revision 738947f0f3cf77baeab5176a2eb50bf9dccc6236)
1186128f7SMauro Carvalho ChehabLinux magic numbers
2186128f7SMauro Carvalho Chehab===================
3186128f7SMauro Carvalho Chehab
4186128f7SMauro Carvalho ChehabThis file is a registry of magic numbers which are in use.  When you
5186128f7SMauro Carvalho Chehabadd a magic number to a structure, you should also add it to this
6186128f7SMauro Carvalho Chehabfile, since it is best if the magic numbers used by various structures
7186128f7SMauro Carvalho Chehabare unique.
8186128f7SMauro Carvalho Chehab
9186128f7SMauro Carvalho ChehabIt is a **very** good idea to protect kernel data structures with magic
10186128f7SMauro Carvalho Chehabnumbers.  This allows you to check at run time whether (a) a structure
11186128f7SMauro Carvalho Chehabhas been clobbered, or (b) you've passed the wrong structure to a
12186128f7SMauro Carvalho Chehabroutine.  This last is especially useful --- particularly when you are
13186128f7SMauro Carvalho Chehabpassing pointers to structures via a void * pointer.  The tty code,
14186128f7SMauro Carvalho Chehabfor example, does this frequently to pass driver-specific and line
15186128f7SMauro Carvalho Chehabdiscipline-specific structures back and forth.
16186128f7SMauro Carvalho Chehab
17*738947f0SMartin KepplingerThe way to use magic numbers is to declare them at the beginning of
18186128f7SMauro Carvalho Chehabthe structure, like so::
19186128f7SMauro Carvalho Chehab
20186128f7SMauro Carvalho Chehab	struct tty_ldisc {
21186128f7SMauro Carvalho Chehab		int	magic;
22186128f7SMauro Carvalho Chehab		...
23186128f7SMauro Carvalho Chehab	};
24186128f7SMauro Carvalho Chehab
25186128f7SMauro Carvalho ChehabPlease follow this discipline when you are adding future enhancements
26186128f7SMauro Carvalho Chehabto the kernel!  It has saved me countless hours of debugging,
27186128f7SMauro Carvalho Chehabespecially in the screwy cases where an array has been overrun and
28186128f7SMauro Carvalho Chehabstructures following the array have been overwritten.  Using this
29186128f7SMauro Carvalho Chehabdiscipline, these cases get detected quickly and safely.
30186128f7SMauro Carvalho Chehab
31186128f7SMauro Carvalho ChehabChangelog::
32186128f7SMauro Carvalho Chehab
33186128f7SMauro Carvalho Chehab					Theodore Ts'o
34186128f7SMauro Carvalho Chehab					31 Mar 94
35186128f7SMauro Carvalho Chehab
36186128f7SMauro Carvalho Chehab  The magic table is current to Linux 2.1.55.
37186128f7SMauro Carvalho Chehab
38186128f7SMauro Carvalho Chehab					Michael Chastain
39186128f7SMauro Carvalho Chehab					<mailto:mec@shout.net>
40186128f7SMauro Carvalho Chehab					22 Sep 1997
41186128f7SMauro Carvalho Chehab
42186128f7SMauro Carvalho Chehab  Now it should be up to date with Linux 2.1.112. Because
43186128f7SMauro Carvalho Chehab  we are in feature freeze time it is very unlikely that
44186128f7SMauro Carvalho Chehab  something will change before 2.2.x. The entries are
45186128f7SMauro Carvalho Chehab  sorted by number field.
46186128f7SMauro Carvalho Chehab
47186128f7SMauro Carvalho Chehab					Krzysztof G. Baranowski
48186128f7SMauro Carvalho Chehab					<mailto: kgb@knm.org.pl>
49186128f7SMauro Carvalho Chehab					29 Jul 1998
50186128f7SMauro Carvalho Chehab
51186128f7SMauro Carvalho Chehab  Updated the magic table to Linux 2.5.45. Right over the feature freeze,
52186128f7SMauro Carvalho Chehab  but it is possible that some new magic numbers will sneak into the
53186128f7SMauro Carvalho Chehab  kernel before 2.6.x yet.
54186128f7SMauro Carvalho Chehab
55186128f7SMauro Carvalho Chehab					Petr Baudis
56186128f7SMauro Carvalho Chehab					<pasky@ucw.cz>
57186128f7SMauro Carvalho Chehab					03 Nov 2002
58186128f7SMauro Carvalho Chehab
59186128f7SMauro Carvalho Chehab  Updated the magic table to Linux 2.5.74.
60186128f7SMauro Carvalho Chehab
61186128f7SMauro Carvalho Chehab					Fabian Frederick
62186128f7SMauro Carvalho Chehab					<ffrederick@users.sourceforge.net>
63186128f7SMauro Carvalho Chehab					09 Jul 2003
64186128f7SMauro Carvalho Chehab
65186128f7SMauro Carvalho Chehab
66186128f7SMauro Carvalho Chehab===================== ================ ======================== ==========================================
67186128f7SMauro Carvalho ChehabMagic Name            Number           Structure                File
68186128f7SMauro Carvalho Chehab===================== ================ ======================== ==========================================
69186128f7SMauro Carvalho ChehabPG_MAGIC              'P'              pg_{read,write}_hdr      ``include/linux/pg.h``
70186128f7SMauro Carvalho ChehabCMAGIC                0x0111           user                     ``include/linux/a.out.h``
71186128f7SMauro Carvalho ChehabMKISS_DRIVER_MAGIC    0x04bf           mkiss_channel            ``drivers/net/mkiss.h``
72186128f7SMauro Carvalho ChehabHDLC_MAGIC            0x239e           n_hdlc                   ``drivers/char/n_hdlc.c``
73186128f7SMauro Carvalho ChehabAPM_BIOS_MAGIC        0x4101           apm_user                 ``arch/x86/kernel/apm_32.c``
74186128f7SMauro Carvalho ChehabCYCLADES_MAGIC        0x4359           cyclades_port            ``include/linux/cyclades.h``
75186128f7SMauro Carvalho ChehabDB_MAGIC              0x4442           fc_info                  ``drivers/net/iph5526_novram.c``
76186128f7SMauro Carvalho ChehabDL_MAGIC              0x444d           fc_info                  ``drivers/net/iph5526_novram.c``
77186128f7SMauro Carvalho ChehabFASYNC_MAGIC          0x4601           fasync_struct            ``include/linux/fs.h``
78186128f7SMauro Carvalho ChehabFF_MAGIC              0x4646           fc_info                  ``drivers/net/iph5526_novram.c``
79186128f7SMauro Carvalho ChehabISICOM_MAGIC          0x4d54           isi_port                 ``include/linux/isicom.h``
80186128f7SMauro Carvalho ChehabPTY_MAGIC             0x5001                                    ``drivers/char/pty.c``
81186128f7SMauro Carvalho ChehabPPP_MAGIC             0x5002           ppp                      ``include/linux/if_pppvar.h``
82186128f7SMauro Carvalho ChehabSERIAL_MAGIC          0x5301           async_struct             ``include/linux/serial.h``
83186128f7SMauro Carvalho ChehabSSTATE_MAGIC          0x5302           serial_state             ``include/linux/serial.h``
84186128f7SMauro Carvalho ChehabSLIP_MAGIC            0x5302           slip                     ``drivers/net/slip.h``
85186128f7SMauro Carvalho ChehabSTRIP_MAGIC           0x5303           strip                    ``drivers/net/strip.c``
86186128f7SMauro Carvalho ChehabX25_ASY_MAGIC         0x5303           x25_asy                  ``drivers/net/x25_asy.h``
87186128f7SMauro Carvalho ChehabSIXPACK_MAGIC         0x5304           sixpack                  ``drivers/net/hamradio/6pack.h``
88186128f7SMauro Carvalho ChehabAX25_MAGIC            0x5316           ax_disp                  ``drivers/net/mkiss.h``
89186128f7SMauro Carvalho ChehabTTY_MAGIC             0x5401           tty_struct               ``include/linux/tty.h``
90186128f7SMauro Carvalho ChehabMGSL_MAGIC            0x5401           mgsl_info                ``drivers/char/synclink.c``
91186128f7SMauro Carvalho ChehabTTY_DRIVER_MAGIC      0x5402           tty_driver               ``include/linux/tty_driver.h``
92186128f7SMauro Carvalho ChehabMGSLPC_MAGIC          0x5402           mgslpc_info              ``drivers/char/pcmcia/synclink_cs.c``
93186128f7SMauro Carvalho ChehabTTY_LDISC_MAGIC       0x5403           tty_ldisc                ``include/linux/tty_ldisc.h``
94186128f7SMauro Carvalho ChehabUSB_SERIAL_MAGIC      0x6702           usb_serial               ``drivers/usb/serial/usb-serial.h``
95186128f7SMauro Carvalho ChehabFULL_DUPLEX_MAGIC     0x6969                                    ``drivers/net/ethernet/dec/tulip/de2104x.c``
96186128f7SMauro Carvalho ChehabUSB_BLUETOOTH_MAGIC   0x6d02           usb_bluetooth            ``drivers/usb/class/bluetty.c``
97186128f7SMauro Carvalho ChehabRFCOMM_TTY_MAGIC      0x6d02                                    ``net/bluetooth/rfcomm/tty.c``
98186128f7SMauro Carvalho ChehabUSB_SERIAL_PORT_MAGIC 0x7301           usb_serial_port          ``drivers/usb/serial/usb-serial.h``
99186128f7SMauro Carvalho ChehabCG_MAGIC              0x00090255       ufs_cylinder_group       ``include/linux/ufs_fs.h``
100186128f7SMauro Carvalho ChehabRPORT_MAGIC           0x00525001       r_port                   ``drivers/char/rocket_int.h``
101186128f7SMauro Carvalho ChehabLSEMAGIC              0x05091998       lse                      ``drivers/fc4/fc.c``
102186128f7SMauro Carvalho ChehabGDTIOCTL_MAGIC        0x06030f07       gdth_iowr_str            ``drivers/scsi/gdth_ioctl.h``
103186128f7SMauro Carvalho ChehabRIEBL_MAGIC           0x09051990                                ``drivers/net/atarilance.c``
104186128f7SMauro Carvalho ChehabNBD_REQUEST_MAGIC     0x12560953       nbd_request              ``include/linux/nbd.h``
105186128f7SMauro Carvalho ChehabRED_MAGIC2            0x170fc2a5       (any)                    ``mm/slab.c``
106186128f7SMauro Carvalho ChehabBAYCOM_MAGIC          0x19730510       baycom_state             ``drivers/net/baycom_epp.c``
107186128f7SMauro Carvalho ChehabISDN_X25IFACE_MAGIC   0x1e75a2b9       isdn_x25iface_proto_data ``drivers/isdn/isdn_x25iface.h``
108186128f7SMauro Carvalho ChehabECP_MAGIC             0x21504345       cdkecpsig                ``include/linux/cdk.h``
109186128f7SMauro Carvalho ChehabLSOMAGIC              0x27091997       lso                      ``drivers/fc4/fc.c``
110186128f7SMauro Carvalho ChehabLSMAGIC               0x2a3b4d2a       ls                       ``drivers/fc4/fc.c``
111186128f7SMauro Carvalho ChehabWANPIPE_MAGIC         0x414C4453       sdla_{dump,exec}         ``include/linux/wanpipe.h``
112186128f7SMauro Carvalho ChehabCS_CARD_MAGIC         0x43525553       cs_card                  ``sound/oss/cs46xx.c``
113186128f7SMauro Carvalho ChehabLABELCL_MAGIC         0x4857434c       labelcl_info_s           ``include/asm/ia64/sn/labelcl.h``
114186128f7SMauro Carvalho ChehabISDN_ASYNC_MAGIC      0x49344C01       modem_info               ``include/linux/isdn.h``
115186128f7SMauro Carvalho ChehabCTC_ASYNC_MAGIC       0x49344C01       ctc_tty_info             ``drivers/s390/net/ctctty.c``
116186128f7SMauro Carvalho ChehabISDN_NET_MAGIC        0x49344C02       isdn_net_local_s         ``drivers/isdn/i4l/isdn_net_lib.h``
117186128f7SMauro Carvalho ChehabSAVEKMSG_MAGIC2       0x4B4D5347       savekmsg                 ``arch/*/amiga/config.c``
118186128f7SMauro Carvalho ChehabCS_STATE_MAGIC        0x4c4f4749       cs_state                 ``sound/oss/cs46xx.c``
119186128f7SMauro Carvalho ChehabSLAB_C_MAGIC          0x4f17a36d       kmem_cache               ``mm/slab.c``
120186128f7SMauro Carvalho ChehabCOW_MAGIC             0x4f4f4f4d       cow_header_v1            ``arch/um/drivers/ubd_user.c``
121186128f7SMauro Carvalho ChehabI810_CARD_MAGIC       0x5072696E       i810_card                ``sound/oss/i810_audio.c``
122186128f7SMauro Carvalho ChehabTRIDENT_CARD_MAGIC    0x5072696E       trident_card             ``sound/oss/trident.c``
123186128f7SMauro Carvalho ChehabROUTER_MAGIC          0x524d4157       wan_device               [in ``wanrouter.h`` pre 3.9]
124186128f7SMauro Carvalho ChehabSAVEKMSG_MAGIC1       0x53415645       savekmsg                 ``arch/*/amiga/config.c``
125186128f7SMauro Carvalho ChehabGDA_MAGIC             0x58464552       gda                      ``arch/mips/include/asm/sn/gda.h``
126186128f7SMauro Carvalho ChehabRED_MAGIC1            0x5a2cf071       (any)                    ``mm/slab.c``
127186128f7SMauro Carvalho ChehabEEPROM_MAGIC_VALUE    0x5ab478d2       lanai_dev                ``drivers/atm/lanai.c``
128186128f7SMauro Carvalho ChehabHDLCDRV_MAGIC         0x5ac6e778       hdlcdrv_state            ``include/linux/hdlcdrv.h``
129186128f7SMauro Carvalho ChehabPCXX_MAGIC            0x5c6df104       channel                  ``drivers/char/pcxx.h``
130186128f7SMauro Carvalho ChehabKV_MAGIC              0x5f4b565f       kernel_vars_s            ``arch/mips/include/asm/sn/klkernvars.h``
131186128f7SMauro Carvalho ChehabI810_STATE_MAGIC      0x63657373       i810_state               ``sound/oss/i810_audio.c``
132186128f7SMauro Carvalho ChehabTRIDENT_STATE_MAGIC   0x63657373       trient_state             ``sound/oss/trident.c``
133186128f7SMauro Carvalho ChehabM3_CARD_MAGIC         0x646e6f50       m3_card                  ``sound/oss/maestro3.c``
134186128f7SMauro Carvalho ChehabFW_HEADER_MAGIC       0x65726F66       fw_header                ``drivers/atm/fore200e.h``
135186128f7SMauro Carvalho ChehabSLOT_MAGIC            0x67267321       slot                     ``drivers/hotplug/cpqphp.h``
136186128f7SMauro Carvalho ChehabSLOT_MAGIC            0x67267322       slot                     ``drivers/hotplug/acpiphp.h``
137186128f7SMauro Carvalho ChehabLO_MAGIC              0x68797548       nbd_device               ``include/linux/nbd.h``
138186128f7SMauro Carvalho ChehabOPROFILE_MAGIC        0x6f70726f       super_block              ``drivers/oprofile/oprofilefs.h``
139186128f7SMauro Carvalho ChehabM3_STATE_MAGIC        0x734d724d       m3_state                 ``sound/oss/maestro3.c``
140186128f7SMauro Carvalho ChehabVMALLOC_MAGIC         0x87654320       snd_alloc_track          ``sound/core/memory.c``
141186128f7SMauro Carvalho ChehabKMALLOC_MAGIC         0x87654321       snd_alloc_track          ``sound/core/memory.c``
142186128f7SMauro Carvalho ChehabPWC_MAGIC             0x89DC10AB       pwc_device               ``drivers/usb/media/pwc.h``
143186128f7SMauro Carvalho ChehabNBD_REPLY_MAGIC       0x96744668       nbd_reply                ``include/linux/nbd.h``
144186128f7SMauro Carvalho ChehabENI155_MAGIC          0xa54b872d       midway_eprom	        ``drivers/atm/eni.h``
145186128f7SMauro Carvalho ChehabCODA_MAGIC            0xC0DAC0DA       coda_file_info           ``fs/coda/coda_fs_i.h``
146186128f7SMauro Carvalho ChehabDPMEM_MAGIC           0xc0ffee11       gdt_pci_sram             ``drivers/scsi/gdth.h``
147186128f7SMauro Carvalho ChehabYAM_MAGIC             0xF10A7654       yam_port                 ``drivers/net/hamradio/yam.c``
148186128f7SMauro Carvalho ChehabCCB_MAGIC             0xf2691ad2       ccb                      ``drivers/scsi/ncr53c8xx.c``
149186128f7SMauro Carvalho ChehabQUEUE_MAGIC_FREE      0xf7e1c9a3       queue_entry              ``drivers/scsi/arm/queue.c``
150186128f7SMauro Carvalho ChehabQUEUE_MAGIC_USED      0xf7e1cc33       queue_entry              ``drivers/scsi/arm/queue.c``
151186128f7SMauro Carvalho ChehabHTB_CMAGIC            0xFEFAFEF1       htb_class                ``net/sched/sch_htb.c``
152186128f7SMauro Carvalho ChehabNMI_MAGIC             0x48414d4d455201 nmi_s                    ``arch/mips/include/asm/sn/nmi.h``
153186128f7SMauro Carvalho Chehab===================== ================ ======================== ==========================================
154186128f7SMauro Carvalho Chehab
155186128f7SMauro Carvalho ChehabNote that there are also defined special per-driver magic numbers in sound
156186128f7SMauro Carvalho Chehabmemory management. See ``include/sound/sndmagic.h`` for complete list of them. Many
157186128f7SMauro Carvalho ChehabOSS sound drivers have their magic numbers constructed from the soundcard PCI
158186128f7SMauro Carvalho ChehabID - these are not listed here as well.
159186128f7SMauro Carvalho Chehab
160186128f7SMauro Carvalho ChehabIrDA subsystem also uses large number of own magic numbers, see
161186128f7SMauro Carvalho Chehab``include/net/irda/irda.h`` for a complete list of them.
162186128f7SMauro Carvalho Chehab
163186128f7SMauro Carvalho ChehabHFS is another larger user of magic numbers - you can find them in
164186128f7SMauro Carvalho Chehab``fs/hfs/hfs.h``.
165