linux/Documentation/process/magic-number.rst
Jiri Slaby 9b12f050c7 char: pcmcia: remove all the drivers
These char PCMCIA drivers are buggy[1] and receive only minimal care. It
was concluded[2], that we should try to remove most pcmcia drivers
completely. Let's start with these char broken one.

Note that I also removed a UAPI header: include/uapi/linux/cm4000_cs.h.
I found only coccinelle tests mentioning some ioctl constants from that
file. But they are not actually used. Anyway, should someone complain,
we may reintroduce the header (or its parts).

[1] https://lore.kernel.org/all/f41c2765-80e0-48bc-b1e4-8cfd3230fd4a@www.fastmail.com/
[2] https://lore.kernel.org/all/c5b39544-a4fb-4796-a046-0b9be9853787@app.fastmail.com/

Signed-off-by: Jiri Slaby (SUSE) <jirislaby@kernel.org>
Cc: "Hyunwoo Kim" <imv4bel@gmail.com>
Cc: Harald Welte <laforge@gnumonks.org>
Cc: Lubomir Rintel <lkundrak@v3.sk>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Dominik Brodowski <linux@dominikbrodowski.net>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20230222092302.6348-2-jirislaby@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2023-03-09 17:30:27 +01:00

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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: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``
===================== ================ ======================== ==========================================