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