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- .. _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:[email protected]>
- 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: [email protected]>
- 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
- <[email protected]>
- 03 Nov 2002
- Updated the magic table to Linux 2.5.74.
- Fabian Frederick
- <[email protected]>
- 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``
- MGSLPC_MAGIC 0x5402 mgslpc_info ``drivers/char/pcmcia/synclink_cs.c``
- 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``
- ===================== ================ ======================== ==========================================
|
