netdev - iproute2: no error message when link up command fails.

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Message-ID: <20080716220058.GA31425@amd64.fatal.se>
Date:	Thu, 17 Jul 2008 00:00:58 +0200
From:	Andreas Henriksson <andreas@...al.se>
To:	stephen.hemminger@...tta.com
Cc:	Johannes Berg <johannes@...solutions.net>, 489340@...s.debian.org,
	netdev@...r.kernel.org
Subject: iproute2: no error message when link up command fails.

Hi Stephen and co.!

Johannes Berg reported that iproute2 doesn't give any error message when
"ip link set ... up" failed for him (as opposed to ifconfig):
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=489340

The ways he suggested didn't work for me to reproduce, but I found out
simply using the wmaster0 device works as a testcase.
(You'll need a wireless device, probably with a driver based on the new
mac80211 stack).

I've debugged this into a place in the bundled rtnetlink library where
if there's a netlink error - it is ignored if there's no errno, which
seems weird. I don't really understand the code, but this "proof of
concept" patch makes "ip link set dev wmaster0 up" spit out an error
message atleast. Could you please have a look at what's going on here?

diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index 5ae64f7..afa58fb 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -351,6 +351,7 @@ int rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n, pid_t peer,
 					if (errno == 0) {
 						if (answer)
 							memcpy(answer, h, h->nlmsg_len);
+						fprintf(stderr, "Unknown netlink error.\n");
 						return 0;
 					}
 					perror("RTNETLINK answers");

For the record, here's what ifconfig says:

$ sudo ifconfig wmaster0 up
SIOCSIFFLAGS: Operation not supported

--
Regards,
Andreas Henriksson
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