linux-kernel - Re: add a new system call

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Message-ID: <20100112155257.GG3925@hack>
Date:	Tue, 12 Jan 2010 23:52:57 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	mojtaba <kernelppc@...il.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: add a new system call

On Tue, Jan 12, 2010 at 02:53:10PM +0100, mojtaba wrote:
>[please cc kernelppc@...il.com  in your replies]
>
>Dear all,
>
>I need to add a new system call to the linux kernel.
>
>These are the linux information:
>Linux ubuntu-desktop 2.6.32.3 #5 SMP Mon Jan 11 16:56:27 CET 2010 i686
>GNU/Linux
>
>I am working on kernel 2.6.32.
>
>These are all the changes I did:
>
>1- adding "	.long sys_mycall" to the end of
>"arch/x86/kernel/syscall_table_32.S"
>
>2- adding
>Code:
>#define __NR_mycall 242
>__SYSCALL(__NR_mycall, sys_mycall)
>#undef __NR_syscalls
>#define __NR_syscalls 243
>to the "include/asm-generic/unistd.h"
>
>3- adding
>asmlinkage long sys_mycall(char * fname, void * params);
>to the end of "/include/linux/syscalls.h"
>
>4-modifying the linux Makefile
>core-y	 += kernel/ mm/ fs/ ipc/ security/ crypto/ block/ mycall/
>
>5- adding mycall folder to kernel source and mycall.c and the
>corresponding Makefile in it:
>Code:
>#include <linux/kernel.h>
>#include <linux/syscalls.h>
>SYSCALL_DEFINE2(mycall, char __user *, fname,void __user *,params)
>{
>printk("I am here !!";
>return 10;
>}


This is not what you did, you can't pass compiling here, since you are
missing ')'...

BTW, You can make a diff to show what you have changed.

>Now after building and installing the new kernel, I want to test the
>system call with this code:
>
>Code:
>#include<stdio.h>
>#include <errno.h>
>#include<linux/unistd.h>
>#include <sys/syscall.h>
>
>#define __NR_mycall 242
>
>long mycall(char * fname, void * params )
>{
>return syscall(__NR_mycall, fname, params);
>}
>
>int main(void)
>{
>int tmp=10;	
>int er=0;	
>char * chp= (char *) &tmp;
>void * vp= (void *) &tmp;
>printf("%d\n", er=mycall(chp,vp));
>if( er < 0 ) {
>printf( "Error: %d, %s\n", errno, strerror( errno ) );
>}
>}
>Unfortunately, the code prints this:
>-1
>Error: 3, No such process
>
>And I have no idea what the problem is!
>
>Is there any body who can help me?
>
>Thank you and best regards,
>Mojtaba
>--
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