2010-03-18 14:37:59 +01:00
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From libc-alpha-return-22754-pasky=ucw.cz@sourceware.org Tue Mar 16 00:47:00 2010
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for <pasky@ucw.cz>; Tue, 16 Mar 2010 00:46:59 +0100 (CET)
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Received: (qmail 18956 invoked by alias); 15 Mar 2010 23:46:58 -0000
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Message-ID: <4B9E6CFA.7020002@riot.org>
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Date: Mon, 15 Mar 2010 18:23:06 +0100
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From: Sebastian Kienzl <seb@riot.org>
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User-Agent: Thunderbird 2.0.0.23 (Windows/20090812)
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MIME-Version: 1.0
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To: libc-alpha@sourceware.org
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Subject: Reloading of /etc/resolv.conf
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Content-Type: multipart/mixed;
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boundary="------------060407080409020101000002"
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This is a multi-part message in MIME format.
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--------------060407080409020101000002
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Content-Type: text/plain; charset=ISO-8859-15; format=flowed
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Content-Transfer-Encoding: 7bit
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Hello!
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There's a patch in the wild against the resolver which makes it reload
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/etc/resolv.conf on change, see
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http://sources.redhat.com/ml/libc-alpha/2004-09/msg00130.html
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However, this patch actually doesn't work properly for multi-threaded
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programs, as only one thread will notice the change and refresh its
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resolver state. I've attached a proper patch. It's for 2.5 but it should
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work with current versions, too.
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Even though the patch may not be interesting for upstream, I decided to
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let you know about this problem, since the mentioned patch seems to be
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used by at least Debian and Ubuntu.
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Regards,
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Seb.
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--------------060407080409020101000002
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Content-Type: text/plain;
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name="glibc-2.5-resolvconf.patch"
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Content-Transfer-Encoding: 7bit
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Content-Disposition: inline;
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filename="glibc-2.5-resolvconf.patch"
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diff -ur resolv.orig/res_libc.c resolv/res_libc.c
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--- resolv.orig/res_libc.c 2005-11-01 01:06:40.000000000 +0100
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+++ resolv/res_libc.c 2010-03-15 14:13:18.000000000 +0100
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@@ -22,7 +22,7 @@
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#include <arpa/nameser.h>
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#include <resolv.h>
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#include <bits/libc-lock.h>
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-
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+#include <sys/stat.h>
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/* The following bit is copied from res_data.c (where it is #ifdef'ed
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out) since res_init() should go into libc.so but the rest of that
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@@ -89,12 +89,34 @@
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return (__res_vinit(&_res, 1));
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}
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+static time_t resconf_mtime;
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+__libc_lock_define_initialized (static, resconf_mtime_lock);
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+
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+/* Check if the modification time of resolv.conf has changed.
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+ If so, have all threads re-initialize their resolver states */
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+static void
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+__res_check_resconf (void)
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+{
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+ struct stat statbuf;
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+ if (stat (_PATH_RESCONF, &statbuf) == 0) {
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+ __libc_lock_lock (resconf_mtime_lock);
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+ if (statbuf.st_mtime != resconf_mtime) {
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+ resconf_mtime = statbuf.st_mtime;
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+ atomicinclock (lock);
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+ atomicinc (__res_initstamp);
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+ atomicincunlock (lock);
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+ }
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+ __libc_lock_unlock (resconf_mtime_lock);
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+ }
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+}
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+
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/* Initialize resp if RES_INIT is not yet set or if res_init in some other
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thread requested re-initializing. */
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int
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__res_maybe_init (res_state resp, int preinit)
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{
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if (resp->options & RES_INIT) {
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+ __res_check_resconf ();
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if (__res_initstamp != resp->_u._ext.initstamp) {
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2010-03-25 17:12:02 +01:00
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if (resp->nscount > 0)
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2010-03-18 14:37:59 +01:00
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__res_iclose (resp, true);
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--------------060407080409020101000002--
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