Enabling message queue in 2.6.10 kernel

Enabling message queue in 2.6.10 kernel

[Chinmaya Mishra]

Hi All,
I am trying for message queue in linux-2.6.10 kernel.
I export sys_msgget(), sys_msgctl(), sys_msgsnd() and sys_msgrcv() in
the kernel with following EXPORT_SYMBOL(sys_msgget) and so on.
Then compile the kernel, boot with the new image.

My code is like this.
#include <linux/module.h>
#include <linux/kernel.h>

#include <linux/types.h>
#include <linux/ipc.h>
#include <linux/msg.h>
#include <linux/syscalls.h>

#include <asm/system.h>

int msqid, ret;
/* this is the thread function that we are executing */
void mymsgSend(void)
{
        struct msgbuf sbuf;
        printk("Start send message \n");
        memset(&sbuf, '\0', sizeof(sbuf));
        if((msqid = sys_msgget((key_t)1234, 0666 | IPC_CREAT )) < 0) {
                printk("Err: sys_msgget \n");
                return ;
        }
        sbuf.mtype = 1;
        //sprintf(sbuf.mtext,"a");
        ret = sys_msgsnd(msqid, &sbuf, sizeof(sbuf), IPC_NOWAIT);
        printk("Send ret = %d \n", ret);
        if (ret < 0) {
                printk("Err: sys_msgsnd \n");
                return ;
        }
        return ;
}

void mymsgRecv(void)
{
        int msqid;
        struct msgbuf rbuf;
        printk("Start recv message  \n");
        memset(&rbuf, '\0', sizeof(rbuf));
        if ((msqid = sys_msgget((key_t)1234, 0666)) < 0) {
                printk("Err: sys_msgget \n");
                return ;
        }
        rbuf.mtype = 1;
        ret = sys_msgrcv(msqid, (struct msgbuf *)&rbuf, sizeof(rbuf), 
rbuf.mtype, IPC_NOWAIT);
        printk("Recv ret = %d \n", ret);
        if (ret < 0) {
                printk("Err: sys_msgrcv \n");
                return ;
        }
        printk("Mesg Recv = %s \n", rbuf.mtext);
        return;
}

/* load the module */
int init_module(void)
{
              mymsgSend();
              msleep(1000);
              mymsgRecv();
        }
        return(0);
}

/* remove the module */
void cleanup_module(void)
{
        printk("Stop Kernel Thread \n");
        sys_msgctl(msqid, IPC_RMID, NULL);
        return;
}


But the out put messages in # dmesg <enter> is like this

Start send message
Send ret = -14
Err: sys_msgsnd
Start recv message
Recv ret = -42
Err: sys_msgrcv
Stop Kernel Thread

Is there any thing I am missing. Please help soon.


With Regards,
Chinmaya.

Re: Enabling message queue in 2.6.10 kernel

[Arjan van de Ven]

> 
> But the out put messages in # dmesg <enter> is like this
> 
> Start send message
> Send ret = -14
> Err: sys_msgsnd
> Start recv message
> Recv ret = -42
> Err: sys_msgrcv
> Stop Kernel Thread
> 
> Is there any thing I am missing. Please help soon.

you're missing that you're calling functions which expect a userspace
pointer, but with a kernel space pointer. You really shouldn't do that,
and in fact it doesn't work the way you did it. (you'd need to call
set_fs() and friends first, but if you're not really careful you open
security holes that way)

Can you explain why you'd want to do this from kernel space in the first
place? It's not unlikely that it's the wrong approach....

Greetings,
   Arjan van de Ven