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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 then 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 screw 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.
Theodore Ts'o
31-Mar-94
Magic Name Number Structure File
===========================================================================
FASYNC_MAGIC 0x4601 struct fasync_struct include/linux/fs.h
PTY_MAGIC 0x5001 struct pty_struct drivers/char/pty.c
PPP_MAGIC 0x5002 struct ppp_struct include/linux/ppp.h
TTY_MAGIC 0x5401 struct tty_struct include/linux/tty.h
TTY_DRIVER_MAGIC 0x5402 struct tty_driver include/linux/tty_driver.h
TTY_LDISC_MAGIC 0x5403 struct tty_ldisc include/linux/tty_ldisc.h
SERIAL_MAGIC 0x5301 struct async_struct include/linux/serial.h
SLIP_MAGIC 0x5302 struct slip drivers/net/slip.h
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