[Pkg-xen-devel] Bug#770456: Bug#770456: Please start a qemu process in domain 0.

[Stefan Bader]

On 27.11.2014 12:18, Ian Campbell wrote:
> On Thu, 2014-11-27 at 11:02 +0100, Stefan Bader wrote:
>> On 21.11.2014 13:50, Ian Campbell wrote:
>>> Package: xen-utils-common
>>> Version: 4.4.0-1
>>> Severity: important
>>> Tags: patch
>>>
>>> Under some circumstances the xl toolstack needs to create a loopback
>>> mount of a guest disk in dom0 (e.g. in order to run pygrub). Depending
>>> on the nature of the guest disk (e.g. qcow2 or raw file image based)
>>> this can require a qemu instance in dom0.
>>>
>>> The upstream xencommons starts such a qemu on boot. The following patch
>>> adds this to the Debian packages init script as well.
>>>
>>> Once I have a bug number for this I will add it to debian/changelog and
>>> push the result to feature/bugNNNN as usual.
>>>
>>> Thanks,
>>> Ian.
>>>
>>
<old path removed>

>> Not sure this already was handled but the --name argument of qemu_stop_real
>> seems a copy-and-paste bug.
> 
> Yes it is, whoops!
> 
>>  Playing with it right now, --exec instead of --name
>> also works out better since qemu-system-i386 is just about too long.
> 
> So it is, so this is probably a good idea.
> 
> Will you send an updated patch once you've finished testing?
> 

So not sure whether the bug processor can handle attachments but Thunderbird
tends to mess things up otherwise. Also I yet have to figure out the location of
the repo to make proper patches (sorry about that).

Anyway attaching the diff between the current init script and the updated one.
There is one thing which I did not include there. That is a work around some
kernel bug (which should be fixed in Debian by now). Just for here I want to
avoid stepping into the case where the new package is installed with the broken
kernel because in that situation the dpkg starts a qemu which cannot attach
properly and in the end both hang and qemu has to be killed hard(er). All a bit
ugly. So this is likely nothing you need but just in case:

(see https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=763831)

-Stefan

 xenstored_start()
 {
        log_progress_msg "xenstored"
+       #
+       # Work-around kernel regression where short name links of
+       # /proc/$$/exe get replaced on rename unconditionally. This
+       # should be fixed in the kernel but hitting a bad kernel is
+       # fatal with starting qemu in dom0 (dpkg/qemu hangs).
+       #
+       if [ -f $XENSTORED_PIDFILE ]; then
+               XSPID="$(cat $XENSTORED_PIDFILE)"
+               XSBIN="$(ls -la /proc/$XSPID/exe 2>/dev/null)"
+               XSBIN="${XSBIN#*-> }"
+               XSBIN="${XSBIN% (deleted)}"
+               if [ "$XSBIN" != "" ]; then
+                       if [ "$(basename $XSBIN)" = "xenstored.dpkg-new" ]; then
+                               return 1
+                       fi
+               fi
+       fi
        start-stop-daemon --start --quiet --pidfile "$XENSTORED_PIDFILE" --exec
"$XENSTORED" --test > /dev/null \


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--- debian/xen-utils-common.xen.init.orig	2014-11-27 17:25:04.378851403 +0100
+++ debian/xen-utils-common.xen.init	2014-11-27 17:27:32.238849961 +0100
@@ -37,6 +37,9 @@ XENCONSOLED="$ROOT"/bin/xenconsoled
 XENCONSOLED_PIDFILE="/var/run/xenconsoled.pid"
 XENSTORED="$ROOT"/bin/xenstored
 XENSTORED_PIDFILE="/var/run/xenstore.pid"
+QEMU=/usr/bin/qemu-system-i386
+QEMU_PIDFILE="/var/run/qemu-dom0.pid"
+QEMU_ARGS="-xen-domid 0 -xen-attach -name dom0 -nographic -M xenpv -daemonize -monitor /dev/null -serial /dev/null -parallel /dev/null"
 
 modules_setup()
 {
@@ -179,10 +182,65 @@ xenconsoled_stop_real()
 	[ "$RETVAL" = 2 ] && return 2
 	start-stop-daemon --stop --quiet --oknodo --retry=0/30/KILL/5 --exec "$XENCONSOLED"
 	[ "$?" = 2 ] && return 2
-	rm -f $PIDFILE
+	rm -f $XENCONSOLED_PIDFILE
 	return "$RETVAL"
 }
 
+qemu_start()
+{
+	[ -x $QEMU ] || return 0
+	log_progress_msg "qemu"
+	qemu_start_real
+	return $?
+}
+
+qemu_stop()
+{
+	[ -x $QEMU ] || return 0
+	log_progress_msg "qemu"
+	qemu_stop_real
+	return $?
+}
+
+qemu_restart()
+{
+	[ -x $QEMU ] || return 0
+	log_progress_msg "qemu"
+	qemu_stop_real
+	case "$?" in
+		0|1)
+		qemu_start_real
+		case "$?" in
+			0) ;;
+			*) return 2 ;;
+		esac
+		;;
+		*) return 2 ;;
+	esac
+	return 0
+}
+
+qemu_start_real()
+{
+	start-stop-daemon --start --quiet --pidfile "$QEMU_PIDFILE" --exec "$QEMU" --test > /dev/null \
+		|| return 1
+	start-stop-daemon --start --quiet --pidfile "$QEMU_PIDFILE" --exec "$QEMU" -- \
+		$QEMU_ARGS -pidfile "$QEMU_PIDFILE" \
+		|| return 2
+}
+
+qemu_stop_real()
+{
+	start-stop-daemon --stop --quiet --retry=TERM/30/KILL/5 --pidfile "$QEMU_PIDFILE" --exec "$QEMU"
+	RETVAL="$?"
+	[ "$RETVAL" = 2 ] && return 2
+	start-stop-daemon --stop --quiet --oknodo --retry=0/30/KILL/5 --exec "$QEMU"
+	[ "$?" = 2 ] && return 2
+	rm -f $QEMU_PIDFILE
+	return "$RETVAL"
+}
+
+
 xenstored_start()
 {
 	log_progress_msg "xenstored"
@@ -227,6 +285,11 @@ case "$1" in
 		0|1) ;;
 		*) log_end_msg 1; exit ;;
 	esac
+	qemu_start
+	case "$?" in
+		0|1) ;;
+		*) log_end_msg 1; exit ;;
+	esac
 	log_end_msg 0
 	;;
   stop)
@@ -237,6 +300,11 @@ case "$1" in
 	esac
 	log_daemon_msg "Stopping $DESC"
 	ret=0
+	qemu_stop
+	case "$?" in
+		0|1) ;;
+		*) ret=1 ;;
+	esac
 	xend_stop
 	case "$?" in
 		0|1) ;;
@@ -257,6 +325,11 @@ case "$1" in
 	esac
 	log_daemon_msg "Restarting $DESC"
 	ret=0
+	qemu_restart
+	case "$?" in
+		0|1) ;;
+		*) ret=1 ;;
+	esac
 	xend_restart
 	case "$?" in
 		0|1) ;;
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