Re: Generic Netlink

["Edouard Thuleau" <thuleau@xxxxxxxxx>]

I tried this code from the acpi source but the problem still the same.
I register the multicast group with "genl_register_mc_group" function
and it works but the genlmsg_put function return  NULL value on the
arm board and the genlmsg_multicast function return ESRCH error on a
x86 pc.

On Nov 12, 2007 10:59 PM, Paul Moore <paul.moore@xxxxxx> wrote:
>
> On Monday 12 November 2007 11:47:04 am Edouard Thuleau wrote:
> > I try to use the generic netlink functionalities in a kernel module.
> >
> > I looked the doc
> > http://www.linux-foundation.org/en/Net:Generic_Netlink_HOWTO and the
> > source code of kernel/taskstats.c in the kernel.
> > I tried to reproduce the example of the doc (look in the attached
> > file) but it doesn't work.
> >
> > I work on a 2.6.23 kernel and on two different architectures, a
> > classic x86 pc and a armv5b board.
> > On the PC the genlmsg_multicast function return an error (-3) and the
> > system crash totally in the next 5 sec (hard reboot).
> > On the arm board, the genlmsg_put function return the NULL value, but
> > the module is unload and the system stay stable.
> >
> > Can you help me ?
> > Doude.
>
> You might want to look at the ACPI code for some examples, a quick look at the
> code shows that it uses Generic Netlink and multicast messages.
>
> --
> paul moore
> linux security @ hp
>

#include <linux/kernel.h>
#include <linux/module.h>
#include <net/sock.h>
#include <linux/netlink.h>
#include <linux/version.h>

#include <linux/rtnetlink.h>
#include <net/genetlink.h>

enum {
	DOC_EXMPL_C_UNSPEC = 0,
	DOC_EXMPL_C_ECHO,
	__DOC_EXMPL_C_MAX,
};
#define DOC_EXMPL_C_MAX (__DOC_EXMPL_C_MAX - 1)

enum {
	DOC_EXMPL_A_UNSPEC = 0,
	DOC_EXMPL_A_MSG,
	__DOC_EXMPL_A_MAX,
};
#define DOC_EXMPL_A_MAX (__DOC_EXMPL_A_MAX - 1)

static struct genl_family doc_exmpl_gnl_family = {
       .id = GENL_ID_GENERATE,
       .name = "DOC_EXMPL",
       .version = 1,
       .maxattr = DOC_EXMPL_A_MAX,
};

static struct genl_multicast_group event_mcgrp_echo = {
	.name = "mc_group_echo",
};
int send(void) {
	struct sk_buff *skb;
	int rc = 0, size;
	void *msg_head;

	size = nla_total_size(0);

	skb = genlmsg_new(size, GFP_KERNEL);
	if (skb == NULL) {
		printk("error on genlmsg_new\n");
		return -ENOMEM;
	}

	/* create the message headers */
	msg_head = genlmsg_put(skb, 0, 0, &doc_exmpl_gnl_family, 0, DOC_EXMPL_C_ECHO);
/*	if (msg_head == NULL) {
		printk("error on genlmsg_put\n");
		rc = -ENOMEM;
		goto failure;
	}
*/
	/* finalize the message */
	genlmsg_end(skb, msg_head);
	
	rc = genlmsg_multicast(skb, 0, event_mcgrp_echo.id, GFP_ATOMIC);
	if (rc != 0) {
		printk("error on genlmsg_multicast %i\n", rc);
		goto failure;
	}

	return rc;

failure:
	printk("Failure\n");
	nlmsg_free(skb);
	genl_unregister_family(&doc_exmpl_gnl_family);
	return rc;
}

int init_mod(void) {
	int err = 0;

	err = genl_register_family(&doc_exmpl_gnl_family);
	if (err < 0) {
		printk("Error register family\n");
		return err;
	}

	printk("Family id : %i\n", doc_exmpl_gnl_family.id);
	
	err = genl_register_mc_group(&doc_exmpl_gnl_family, &event_mcgrp_echo);

	if (err) {
		genl_unregister_family(&doc_exmpl_gnl_family);
		printk("error register multicast group \n");
		return err;
	}

	return send();
}

static void __exit exit_mod(void) {
	genl_unregister_family(&doc_exmpl_gnl_family);

	printk(KERN_INFO "Goodbye\n");
}

module_init(init_mod);
module_exit(exit_mod);

MODULE_LICENSE("GPL");