From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Ward Subject: [RFC] iproute2: gracefully exit from rtnl_listen() Date: Tue, 1 Sep 2009 17:41:26 -0400 Message-ID: <1251841286-32463-1-git-send-email-david.ward@ll.mit.edu> Cc: David Ward To: netdev@vger.kernel.org Return-path: Received: from LLMAIL1.LL.MIT.EDU ([129.55.12.41]:38359 "EHLO ll.mit.edu" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752595AbZIAWYY (ORCPT ); Tue, 1 Sep 2009 18:24:24 -0400 Received: (from smtp@localhost) by ll.mit.edu (8.12.10/8.8.8) id n81Lm05i008814 for ; Tue, 1 Sep 2009 17:48:00 -0400 (EDT) Sender: netdev-owner@vger.kernel.org List-ID: rtnl_listen() (in iproute2's libnetlink) allows a userspace application to monitor an RTNETLINK multicast group, so that the application can react to changes in the kernel's routing table, neighbor cache, etc. as they occur. (This is in contrast with using RTNETLINK to solicit the kernel for a full copy of the routing table or neighbor cache at a specific point in time.) However rtnl_listen() creates an infinite loop, which does not break in the absence of errors, so there does not seem to be any way to gracefully exit from it. Existing applications that call rtnl_listen(), such as rtmon, break from this loop by terminating the entire application. There should be some mechanism for stopping rtnl_listen() and continuing program execution. If you assume that rtnl_listen() will only need to be stopped because the application has received a signal (such as SIGINT), then the application's signal handler can call rtnl_close() to close the RTNETLINK socket. Afterwards, with this patch, rtnl_listen() can detect that the socket was closed during the interrupt and exit. I am offering this as a starting point for consideration, but I feel that this is at best a poor solution. What is a better way to fix rtnl_listen() (and similar libnetlink functions for consistency)? --- lib/libnetlink.c | 15 ++++++++++++--- 1 files changed, 12 insertions(+), 3 deletions(-) diff --git a/lib/libnetlink.c b/lib/libnetlink.c index b68e2fd..afb5b23 100644 --- a/lib/libnetlink.c +++ b/lib/libnetlink.c @@ -196,8 +196,11 @@ int rtnl_dump_filter(struct rtnl_handle *rth, status = recvmsg(rth->fd, &msg, 0); if (status < 0) { - if (errno == EINTR || errno == EAGAIN) + if (errno == EINTR || errno == EAGAIN) { + if (rth->fd < 0) + return 0; continue; + } fprintf(stderr, "netlink receive error %s (%d)\n", strerror(errno), errno); return -1; @@ -300,8 +303,11 @@ int rtnl_talk(struct rtnl_handle *rtnl, struct nlmsghdr *n, pid_t peer, status = recvmsg(rtnl->fd, &msg, 0); if (status < 0) { - if (errno == EINTR || errno == EAGAIN) + if (errno == EINTR || errno == EAGAIN) { + if (rtnl->fd < 0) + return 0; continue; + } fprintf(stderr, "netlink receive error %s (%d)\n", strerror(errno), errno); return -1; @@ -405,8 +411,11 @@ int rtnl_listen(struct rtnl_handle *rtnl, status = recvmsg(rtnl->fd, &msg, 0); if (status < 0) { - if (errno == EINTR || errno == EAGAIN) + if (errno == EINTR || errno == EAGAIN) { + if (rtnl->fd < 0) + return 0; continue; + } fprintf(stderr, "netlink receive error %s (%d)\n", strerror(errno), errno); return -1; -- 1.5.5.6