| .. _magicnumbers: |
| |
| Linux magic numbers |
| =================== |
| |
| This file is a registry of magic numbers which are in use. When you |
| add a magic number to a structure, you should also add it to this |
| file, since it is best if the magic numbers used by various structures |
| are unique. |
| |
| It is a **very** good idea to protect kernel data structures with magic |
| numbers. This allows you to check at run time whether (a) a structure |
| has been clobbered, or (b) you've passed the wrong structure to a |
| routine. This last is especially useful --- particularly when you are |
| passing pointers to structures via a void * pointer. The tty code, |
| for example, does this frequently to pass driver-specific and line |
| discipline-specific structures back and forth. |
| |
| The way to use magic numbers is to declare them at the beginning of |
| the structure, like so:: |
| |
| struct tty_ldisc { |
| int magic; |
| ... |
| }; |
| |
| Please follow this discipline when you are adding future enhancements |
| to the kernel! It has saved me countless hours of debugging, |
| especially in the screwy cases where an array has been overrun and |
| structures following the array have been overwritten. Using this |
| discipline, these cases get detected quickly and safely. |
| |
| Changelog:: |
| |
| Theodore Ts'o |
| 31 Mar 94 |
| |
| The magic table is current to Linux 2.1.55. |
| |
| Michael Chastain |
| <mailto:mec@shout.net> |
| 22 Sep 1997 |
| |
| Now it should be up to date with Linux 2.1.112. Because |
| we are in feature freeze time it is very unlikely that |
| something will change before 2.2.x. The entries are |
| sorted by number field. |
| |
| Krzysztof G. Baranowski |
| <mailto: kgb@knm.org.pl> |
| 29 Jul 1998 |
| |
| Updated the magic table to Linux 2.5.45. Right over the feature freeze, |
| but it is possible that some new magic numbers will sneak into the |
| kernel before 2.6.x yet. |
| |
| Petr Baudis |
| <pasky@ucw.cz> |
| 03 Nov 2002 |
| |
| Updated the magic table to Linux 2.5.74. |
| |
| Fabian Frederick |
| <ffrederick@users.sourceforge.net> |
| 09 Jul 2003 |
| |
| |
| ===================== ================ ======================== ========================================== |
| Magic Name Number Structure File |
| ===================== ================ ======================== ========================================== |
| PG_MAGIC 'P' pg_{read,write}_hdr ``include/linux/pg.h`` |
| APM_BIOS_MAGIC 0x4101 apm_user ``arch/x86/kernel/apm_32.c`` |
| FASYNC_MAGIC 0x4601 fasync_struct ``include/linux/fs.h`` |
| SLIP_MAGIC 0x5302 slip ``drivers/net/slip.h`` |
| BAYCOM_MAGIC 0x19730510 baycom_state ``drivers/net/baycom_epp.c`` |
| HDLCDRV_MAGIC 0x5ac6e778 hdlcdrv_state ``include/linux/hdlcdrv.h`` |
| KV_MAGIC 0x5f4b565f kernel_vars_s ``arch/mips/include/asm/sn/klkernvars.h`` |
| CODA_MAGIC 0xC0DAC0DA coda_file_info ``fs/coda/coda_fs_i.h`` |
| YAM_MAGIC 0xF10A7654 yam_port ``drivers/net/hamradio/yam.c`` |
| CCB_MAGIC 0xf2691ad2 ccb ``drivers/scsi/ncr53c8xx.c`` |
| QUEUE_MAGIC_FREE 0xf7e1c9a3 queue_entry ``drivers/scsi/arm/queue.c`` |
| QUEUE_MAGIC_USED 0xf7e1cc33 queue_entry ``drivers/scsi/arm/queue.c`` |
| NMI_MAGIC 0x48414d4d455201 nmi_s ``arch/mips/include/asm/sn/nmi.h`` |
| ===================== ================ ======================== ========================================== |
