Re: Detecting link up

[Richard B. Johnson]

On Wed, 18 May 2005, Vaibhav Nivargi wrote:

> try looking at the ioctls which mii-tool / ethtool make
>
> regards,
> Vaibhav
>
> On 5/18/05, Martin Zwickel <martin.zwickel@xxxxxxxxxxxxxx> wrote:
> > On Wed, 18 May 2005 11:35:12 +0100
> > Filipe Abrantes <fla@xxxxxxxxxxxxx> bubbled:
> >
> > > Hi all,
> > >
> > > I need to detect when an interface (wired ethernet) has link up/down.
> > > Is  there a system signal which is sent when this happens? What is the
> > > best  way to this programatically?
> >
> > mii-tool?
> >
> > --
> > MyExcuse:
> > Not enough interrupts

> > Martin Zwickel <martin.zwickel@xxxxxxxxxxxxxx>
> > Research & Development
> >
> > TechnoTrend AG <http://www.technotrend.de>



Cut from some working project........


#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <signal.h>
#include <errno.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <stdint.h>
#include <net/if.h>
#include <netinet/in.h>

typedef uint32_t u32;
typedef uint16_t u16;
typedef uint8_t  u8;

#include <linux/sockios.h>
#include <linux/ethtool.h>

// -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-= 
//
//  Get the link status. This returns TRUE if the link is up and FALSE
//  otherwise.
//
int32_t link_stat()
{
    int s;
    struct ifreq ifr;
    struct ethtool_value eth;
    if((s = socket(AF_INET, SOCK_DGRAM, IPPROTO_IP)) == FAIL)
        ERRORS(Socket);
    bzero(&ifr, sizeof(ifr));
    strcpy(ifr.ifr_name, Eth0);
    ifr.ifr_data = (caddr_t) &eth;
    eth.cmd      = ETHTOOL_GLINK;
    if(ioctl(s, SIOCETHTOOL, &ifr) == FAIL)
        ERRORS(Ioctl);
    (void)close(s);
    return (eth.data) ? TRUE:FALSE;
}


ERRORS, TRUE, FALSE, Eth0, FAIL are macros that you should be able
to figure out for yourself. Maybe you don't have bzero() you
can use memset(x, 0x00, n).


Cheers,
Dick Johnson
Penguin : Linux version 2.6.11.9 on an i686 machine (5537.79 BogoMips).
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