Re: problem with syscall macro

[linux-os]

On Wed, 12 Jan 2005, sounak chakraborty wrote:

>  i am writing a program which willcopy all the lines
> from system log file /var/log/messages and put it in a
> user log file
> i am using syslog with syscall3 but when i am using
> write system cal it is not able to write anything
> do i have to add something more
> i have added the syscall3 macro for write too
> do i have to do it for open system call also
> i am little bit confuse with the kernel-user mode
> switching concept too
> could you please help me out
> thans
> sounak

You are very confused. The "stuff" that comes from the
kernel, printk(), etc., is buffered by the kernel and
then read by user-mode code from /proc/kmsg.

But, once you read it, it's gone. Therefore there is
a procedure,  int syslog(int type, char *buf, int buf_len);
that allows a user to read/manuiplate the logging
facility. `man syslog` will get you that information.
You do __not__ use _syscall3(). See the underscore in
the name? Things that begin with underscores are used by
the 'C' runtime library, not you directly.

#include <stdio.h>
#include <sys/syslog.h>
int main() {
    char buf[0x2000];
    syslog(3, buf, sizeof(buf));
    puts(buf);
    return 0;
}

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