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