Re: Adding a new system call from a module in 2.6

[linux-os]

On Fri, 14 Jan 2005, Avishay Traeger wrote:

> Now that the sys_call_table is no longer exported, what would be the
> best way to add a new system call from a module in 2.6?  I have only
> seen the system call table in assembly code (such as in
> arch/i386/kernel/entry.S) and do not know how to export it.  I know that
> doing this is not recommended, but it would save me a lot of time while
> developing new system calls (no need to recompile kernel and reboot for
> every change).  Thanks in advance for any suggestions.
>
> Avishay Traeger

Just add some dummy function pointers at the end of the table
and have them point to a procedure that returns -ENOSYS.

	existing:

	.long	sys_request_key
	.long	sys_keyctl
syscall_table_size = (. -sys_call_table)

	new:

	.long	sys_request_key
	.long	sys_keyctl
mine:	.long	sys_in_syscall
	.long	sys_in_syscall
	.long	sys_in_syscall
	.long	sys_in_syscall

.global	mine
.type	mine,@object

syscall_table_size = (. -sys_call_table)

Export whatever you want to find your entries in your module.
Your module modifies the pointers at will ('mine' is now an
array of 4 pointers). To prevent crashes, save what was in
the pointer you modified and put it back before your module exits!

Just don't expect this to be put into a standard kernel.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.10 on an i686 machine (5537.79 BogoMips).
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