linux-kernel - Re: Question about SIOCGIFCONF

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Date:	Fri, 28 May 2010 06:57:31 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jeffrey Merkey <jeffmerkey@...il.com>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Question about SIOCGIFCONF

Le jeudi 27 mai 2010 à 21:02 -0600, Jeffrey Merkey a écrit :
> Why is SIOGICONF only instrumented to return a single interface lo for
> example.  I noticed that ifconfig always uses /proc/net/dev but the
> older SIOCGIFCONF ioctl seems to be busted.  Anyone have an
> explanation or is this just how the shit is these days or is the
> fucking thing broken (seems to be). ?

Shit comes from you eyes maybe ?

Correction : Shit comes from your eyes, definitely.

Proof :

# strace -o /tmp/STRACE ifconfig -a
# grep SIOCGIFCONF /tmp/STRACE
ioctl(4, SIOCGIFCONF, {120, {{"lo", {AF_INET, inet_addr("127.0.0.1")}},
{"wlan0", {AF_INET, inet_addr("192.168.1.21")}}, {"ppp0", {AF_INET,
inet_addr("10.150.51.210")}}}}) = 0


Part of ifconfig :

    ifc.ifc_buf = NULL;
    for (;;) {
        ifc.ifc_len = sizeof(struct ifreq) * numreqs;
        ifc.ifc_buf = xrealloc(ifc.ifc_buf, ifc.ifc_len);

        if (ioctl(skfd, SIOCGIFCONF, &ifc) < 0) {
            perror("SIOCGIFCONF");
            goto out;
        }
        if (ifc.ifc_len == sizeof(struct ifreq) * numreqs) {
            /* assume it overflowed and try again */
            numreqs += 10;
            continue;
        }
        break;
    }

maybe numreqs should be firt initialized to 64, then doubled each
round...


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