linux/Documentation/process/magic-number.rst
Linus Torvalds e8bc52cb8d Driver core changes for 6.1-rc1
Here is the big set of driver core and debug printk changes for 6.1-rc1.
 Included in here is:
 	- dynamic debug updates for the core and the drm subsystem.  The
 	  drm changes have all been acked by the relevant maintainers.
 	- kernfs fixes for syzbot reported problems
 	- kernfs refactors and updates for cgroup requirements
 	- magic number cleanups and removals from the kernel tree (they
 	  were not being used and they really did not actually do
 	  anything.)
 	- other tiny cleanups
 
 All of these have been in linux-next for a while with no reported
 issues.
 
 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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Merge tag 'driver-core-6.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core

Pull driver core updates from Greg KH:
 "Here is the big set of driver core and debug printk changes for
  6.1-rc1. Included in here is:

   - dynamic debug updates for the core and the drm subsystem. The drm
     changes have all been acked by the relevant maintainers

   - kernfs fixes for syzbot reported problems

   - kernfs refactors and updates for cgroup requirements

   - magic number cleanups and removals from the kernel tree (they were
     not being used and they really did not actually do anything)

   - other tiny cleanups

  All of these have been in linux-next for a while with no reported
  issues"

* tag 'driver-core-6.1-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core: (74 commits)
  docs: filesystems: sysfs: Make text and code for ->show() consistent
  Documentation: NBD_REQUEST_MAGIC isn't a magic number
  a.out: restore CMAGIC
  device property: Add const qualifier to device_get_match_data() parameter
  drm_print: add _ddebug descriptor to drm_*dbg prototypes
  drm_print: prefer bare printk KERN_DEBUG on generic fn
  drm_print: optimize drm_debug_enabled for jump-label
  drm-print: add drm_dbg_driver to improve namespace symmetry
  drm-print.h: include dyndbg header
  drm_print: wrap drm_*_dbg in dyndbg descriptor factory macro
  drm_print: interpose drm_*dbg with forwarding macros
  drm: POC drm on dyndbg - use in core, 2 helpers, 3 drivers.
  drm_print: condense enum drm_debug_category
  debugfs: use DEFINE_SHOW_ATTRIBUTE to define debugfs_regset32_fops
  driver core: use IS_ERR_OR_NULL() helper in device_create_groups_vargs()
  Documentation: ENI155_MAGIC isn't a magic number
  Documentation: NBD_REPLY_MAGIC isn't a magic number
  nbd: remove define-only NBD_MAGIC, previously magic number
  Documentation: FW_HEADER_MAGIC isn't a magic number
  Documentation: EEPROM_MAGIC_VALUE isn't a magic number
  ...
2022-10-07 17:04:10 -07:00

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ReStructuredText

.. _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``
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``
===================== ================ ======================== ==========================================