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Message-ID: <20140409095556.701e0363@ncopa-desktop.alpinelinux.org>
Date: Wed, 9 Apr 2014 09:55:56 +0200
From: Natanael Copa <ncopa@...inelinux.org>
To: musl@...ts.openwall.com
Cc: dalias@...ifal.cx, justin@...cialbusservice.com
Subject: Re: if_nameindex/getifaddrs and dhcpcd issue
On Tue, 8 Apr 2014 11:45:37 -0400
Rich Felker <dalias@...ifal.cx> wrote:
> > We should not be looking at dhcpd. It's the APIs musl implements:
> > getifaddrs() and if_nameindex() - they are not currently exposing all
> > the information they should.
>
> One can argue about what if_nameindex should expose;
Yes. This is the real issue at hand. What dhcpcd does is not that
relevant here.
> for instance,
> should it expose all possible interface names the kernel could
> support, even with modules that haven't been loaded yet?
IMHO, no. I think it should only expose what you normally find
as /sys/class/net/* (you find same list in /proc/net/dev)
A use case if_nameindex() that I think would be valid is a network config ui.
Which interface do you want to configure?
Presents a list of currently available network interfaces. (from if_nameindex)
It has a button 'Add virtual interface', which lets user configure
bonding/bridges/vlans etc.
(yes, no application should assume that the listed interface actually
works. I could select my USB ethernet dongle and before press 'ok' I
could pull out the USB ethernet...)
> The only
> thing a strictly conforming application can _DO_ with interface
> names/numbers is use them for link-local ipv6 scope ids (this is
> presumably why these functions were added to POSIX in the first
> place). So, from a conformance standpoint, only exposing ids that
> could actually appear on a link-local address (i.e. configured
> interfaces that have ipv6 link-local addresses) would be sufficient.
Then, from a conformance standpoint, the current musl if_nameindex
implementation is broken. It only lists interfaces with configured
ipv4 addresses.
To test yourself:
modprobe dummy
ip link set up dev dummy0
ip addr #verify that dummy has ipv6 link-local
Then run the following testcase:
#include <net/if.h>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
int
main(int argc, char *argv[])
{
struct if_nameindex *if_ni, *i;
if_ni = if_nameindex();
if (if_ni == NULL) {
perror("if_nameindex");
exit(EXIT_FAILURE);
}
for (i = if_ni; ! (i->if_index == 0 && i->if_name == NULL); i++)
printf("%u: %s\n", i->if_index, i->if_name);
if_freenameindex(if_ni);
exit(EXIT_SUCCESS);
}
The ipv6 link-local configured dummy0 interface will not be listed.
-nc
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