Root/Documentation/magic-number.txt

1This file is a registry of magic numbers which are in use. When you
2add a magic number to a structure, you should also add it to this
3file, since it is best if the magic numbers used by various structures
4are unique.
5
6It is a *very* good idea to protect kernel data structures with magic
7numbers. This allows you to check at run time whether (a) a structure
8has been clobbered, or (b) you've passed the wrong structure to a
9routine. This last is especially useful --- particularly when you are
10passing pointers to structures via a void * pointer. The tty code,
11for example, does this frequently to pass driver-specific and line
12discipline-specific structures back and forth.
13
14The way to use magic numbers is to declare then at the beginning of
15the structure, like so:
16
17struct tty_ldisc {
18    int magic;
19    ...
20};
21
22Please follow this discipline when you are adding future enhancements
23to the kernel! It has saved me countless hours of debugging,
24especially in the screwy cases where an array has been overrun and
25structures following the array have been overwritten. Using this
26discipline, these cases get detected quickly and safely.
27
28                    Theodore Ts'o
29                    31 Mar 94
30
31The magic table is current to Linux 2.1.55.
32
33                    Michael Chastain
34                    <mailto:mec@shout.net>
35                    22 Sep 1997
36
37Now it should be up to date with Linux 2.1.112. Because
38we are in feature freeze time it is very unlikely that
39something will change before 2.2.x. The entries are
40sorted by number field.
41
42                    Krzysztof G. Baranowski
43                    <mailto: kgb@knm.org.pl>
44                    29 Jul 1998
45
46Updated the magic table to Linux 2.5.45. Right over the feature freeze,
47but it is possible that some new magic numbers will sneak into the
48kernel before 2.6.x yet.
49
50                    Petr Baudis
51                    <pasky@ucw.cz>
52                    03 Nov 2002
53
54Updated the magic table to Linux 2.5.74.
55
56                    Fabian Frederick
57                    <ffrederick@users.sourceforge.net>
58                    09 Jul 2003
59
60
61Magic Name Number Structure File
62===========================================================================
63PG_MAGIC 'P' pg_{read,write}_hdr include/linux/pg.h
64CMAGIC 0x0111 user include/linux/a.out.h
65MKISS_DRIVER_MAGIC 0x04bf mkiss_channel drivers/net/mkiss.h
66RISCOM8_MAGIC 0x0907 riscom_port drivers/char/riscom8.h
67SPECIALIX_MAGIC 0x0907 specialix_port drivers/char/specialix_io8.h
68HDLC_MAGIC 0x239e n_hdlc drivers/char/n_hdlc.c
69APM_BIOS_MAGIC 0x4101 apm_user arch/x86/kernel/apm_32.c
70CYCLADES_MAGIC 0x4359 cyclades_port include/linux/cyclades.h
71DB_MAGIC 0x4442 fc_info drivers/net/iph5526_novram.c
72DL_MAGIC 0x444d fc_info drivers/net/iph5526_novram.c
73FASYNC_MAGIC 0x4601 fasync_struct include/linux/fs.h
74FF_MAGIC 0x4646 fc_info drivers/net/iph5526_novram.c
75ISICOM_MAGIC 0x4d54 isi_port include/linux/isicom.h
76PTY_MAGIC 0x5001 drivers/char/pty.c
77PPP_MAGIC 0x5002 ppp include/linux/if_pppvar.h
78SERIAL_MAGIC 0x5301 async_struct include/linux/serial.h
79SSTATE_MAGIC 0x5302 serial_state include/linux/serial.h
80SLIP_MAGIC 0x5302 slip drivers/net/slip.h
81STRIP_MAGIC 0x5303 strip drivers/net/strip.c
82X25_ASY_MAGIC 0x5303 x25_asy drivers/net/x25_asy.h
83SIXPACK_MAGIC 0x5304 sixpack drivers/net/hamradio/6pack.h
84AX25_MAGIC 0x5316 ax_disp drivers/net/mkiss.h
85ESP_MAGIC 0x53ee esp_struct drivers/char/esp.h
86TTY_MAGIC 0x5401 tty_struct include/linux/tty.h
87MGSL_MAGIC 0x5401 mgsl_info drivers/char/synclink.c
88TTY_DRIVER_MAGIC 0x5402 tty_driver include/linux/tty_driver.h
89MGSLPC_MAGIC 0x5402 mgslpc_info drivers/char/pcmcia/synclink_cs.c
90TTY_LDISC_MAGIC 0x5403 tty_ldisc include/linux/tty_ldisc.h
91USB_SERIAL_MAGIC 0x6702 usb_serial drivers/usb/serial/usb-serial.h
92FULL_DUPLEX_MAGIC 0x6969 drivers/net/tulip/de2104x.c
93USB_BLUETOOTH_MAGIC 0x6d02 usb_bluetooth drivers/usb/class/bluetty.c
94RFCOMM_TTY_MAGIC 0x6d02 net/bluetooth/rfcomm/tty.c
95USB_SERIAL_PORT_MAGIC 0x7301 usb_serial_port drivers/usb/serial/usb-serial.h
96CG_MAGIC 0x00090255 ufs_cylinder_group include/linux/ufs_fs.h
97A2232_MAGIC 0x000a2232 gs_port drivers/char/ser_a2232.h
98RPORT_MAGIC 0x00525001 r_port drivers/char/rocket_int.h
99LSEMAGIC 0x05091998 lse drivers/fc4/fc.c
100GDTIOCTL_MAGIC 0x06030f07 gdth_iowr_str drivers/scsi/gdth_ioctl.h
101RIEBL_MAGIC 0x09051990 drivers/net/atarilance.c
102RIO_MAGIC 0x12345678 gs_port drivers/char/rio/rio_linux.c
103SX_MAGIC 0x12345678 gs_port drivers/char/sx.h
104NBD_REQUEST_MAGIC 0x12560953 nbd_request include/linux/nbd.h
105RED_MAGIC2 0x170fc2a5 (any) mm/slab.c
106BAYCOM_MAGIC 0x19730510 baycom_state drivers/net/baycom_epp.c
107ISDN_X25IFACE_MAGIC 0x1e75a2b9 isdn_x25iface_proto_data
108                                                    drivers/isdn/isdn_x25iface.h
109ECP_MAGIC 0x21504345 cdkecpsig include/linux/cdk.h
110LSOMAGIC 0x27091997 lso drivers/fc4/fc.c
111LSMAGIC 0x2a3b4d2a ls drivers/fc4/fc.c
112WANPIPE_MAGIC 0x414C4453 sdla_{dump,exec} include/linux/wanpipe.h
113CS_CARD_MAGIC 0x43525553 cs_card sound/oss/cs46xx.c
114LABELCL_MAGIC 0x4857434c labelcl_info_s include/asm/ia64/sn/labelcl.h
115ISDN_ASYNC_MAGIC 0x49344C01 modem_info include/linux/isdn.h
116CTC_ASYNC_MAGIC 0x49344C01 ctc_tty_info drivers/s390/net/ctctty.c
117ISDN_NET_MAGIC 0x49344C02 isdn_net_local_s drivers/isdn/i4l/isdn_net_lib.h
118SAVEKMSG_MAGIC2 0x4B4D5347 savekmsg arch/*/amiga/config.c
119STLI_BOARDMAGIC 0x4bc6c825 stlibrd include/linux/istallion.h
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 include/linux/wanrouter.h
126SCC_MAGIC 0x52696368 gs_port drivers/char/scc.h
127SAVEKMSG_MAGIC1 0x53415645 savekmsg arch/*/amiga/config.c
128GDA_MAGIC 0x58464552 gda arch/mips/include/asm/sn/gda.h
129RED_MAGIC1 0x5a2cf071 (any) mm/slab.c
130STL_PORTMAGIC 0x5a7182c9 stlport include/linux/stallion.h
131EEPROM_MAGIC_VALUE 0x5ab478d2 lanai_dev drivers/atm/lanai.c
132HDLCDRV_MAGIC 0x5ac6e778 hdlcdrv_state include/linux/hdlcdrv.h
133EPCA_MAGIC 0x5c6df104 channel include/linux/epca.h
134PCXX_MAGIC 0x5c6df104 channel drivers/char/pcxx.h
135KV_MAGIC 0x5f4b565f kernel_vars_s arch/mips/include/asm/sn/klkernvars.h
136I810_STATE_MAGIC 0x63657373 i810_state sound/oss/i810_audio.c
137TRIDENT_STATE_MAGIC 0x63657373 trient_state sound/oss/trident.c
138M3_CARD_MAGIC 0x646e6f50 m3_card sound/oss/maestro3.c
139FW_HEADER_MAGIC 0x65726F66 fw_header drivers/atm/fore200e.h
140SLOT_MAGIC 0x67267321 slot drivers/hotplug/cpqphp.h
141SLOT_MAGIC 0x67267322 slot drivers/hotplug/acpiphp.h
142LO_MAGIC 0x68797548 nbd_device include/linux/nbd.h
143OPROFILE_MAGIC 0x6f70726f super_block drivers/oprofile/oprofilefs.h
144M3_STATE_MAGIC 0x734d724d m3_state sound/oss/maestro3.c
145STL_PANELMAGIC 0x7ef621a1 stlpanel include/linux/stallion.h
146VMALLOC_MAGIC 0x87654320 snd_alloc_track sound/core/memory.c
147KMALLOC_MAGIC 0x87654321 snd_alloc_track sound/core/memory.c
148PWC_MAGIC 0x89DC10AB pwc_device drivers/usb/media/pwc.h
149NBD_REPLY_MAGIC 0x96744668 nbd_reply include/linux/nbd.h
150STL_BOARDMAGIC 0xa2267f52 stlbrd include/linux/stallion.h
151ENI155_MAGIC 0xa54b872d midway_eprom drivers/atm/eni.h
152SCI_MAGIC 0xbabeface gs_port drivers/char/sh-sci.h
153CODA_MAGIC 0xC0DAC0DA coda_file_info fs/coda/coda_fs_i.h
154DPMEM_MAGIC 0xc0ffee11 gdt_pci_sram drivers/scsi/gdth.h
155STLI_PORTMAGIC 0xe671c7a1 stliport include/linux/istallion.h
156YAM_MAGIC 0xF10A7654 yam_port drivers/net/hamradio/yam.c
157CCB_MAGIC 0xf2691ad2 ccb drivers/scsi/ncr53c8xx.c
158QUEUE_MAGIC_FREE 0xf7e1c9a3 queue_entry drivers/scsi/arm/queue.c
159QUEUE_MAGIC_USED 0xf7e1cc33 queue_entry drivers/scsi/arm/queue.c
160HTB_CMAGIC 0xFEFAFEF1 htb_class net/sched/sch_htb.c
161NMI_MAGIC 0x48414d4d455201 nmi_s arch/mips/include/asm/sn/nmi.h
162
163Note that there are also defined special per-driver magic numbers in sound
164memory management. See include/sound/sndmagic.h for complete list of them. Many
165OSS sound drivers have their magic numbers constructed from the soundcard PCI
166ID - these are not listed here as well.
167
168IrDA subsystem also uses large number of own magic numbers, see
169include/net/irda/irda.h for a complete list of them.
170
171HFS is another larger user of magic numbers - you can find them in
172fs/hfs/hfs.h.
173

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