Re: locked hotplug scripts

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

On Wed, Mar 30, 2016 at 09:17:24AM +0200, Manuel Bouyer wrote:
> On Wed, Mar 30, 2016 at 12:19:57AM +0200, Christoph Badura wrote:
> > DomU creation with xl with file backed disks fails in vnd allocation
> > because xl runs the hotplug scripts in parallel.  C.f. port-xen/50659 and
> > pkg/51008.
> > 
> > Would people please test the attached scripts by installing them in the
> > appropriate xen/scripts directory?  I'd like to commit them as soonish.
> > 
> > I've tested them locally and they work for me.
> 
> I think you don't need to lock at all when unconfiguring (case 6).
> In the 2) case, I think you only need locking in the file) case.
> The xenstore-write probably can be done unlocked.

I've installed the attached script on my test server. This is the dom0
doing nightly anita xen runs, so we should have several domains
creation/shutdown per day, with 2 file-backed virtual disks.

-- 
Manuel Bouyer <bouyer%antioche.eu.org@localhost>
     NetBSD: 26 ans d'experience feront toujours la difference
--

#!/bin/sh -e

# $NetBSD: block-nbsd,v 1.1.1.1 2008/08/07 20:26:57 cegger Exp $
# Called by xenbackendd
# Usage: block xsdir_backend_path state

DIR=$(dirname "$0")
. "${DIR}/hotplugpath.sh"
. "${DIR}/locking.sh"

PATH=${BINDIR}:${SBINDIR}:${LIBEXEC_BIN}:/bin:/usr/bin:/sbin:/usr/sbin
export PATH

error() {
	echo "$@" >&2
	xenstore-write $xpath/hotplug-status error \
	               $xpath/hotplug-error "$@"
	exit 1
}
	

xpath=$1
xstatus=$2
xparams=$(xenstore-read "$xpath/params")
if [ -b "$xparams" ]; then
	xtype="phy"
elif [ -f "$xparams" ]; then
	xtype="file"
elif [ -z "$xparams" ]; then
	error "$xpath/params is empty, unable to attach block device."
else
	error "$xparams is not a valid file type to use as block device." \
	      "Only block and regular image files accepted."
fi

case $xstatus in
6)
	# device removed
	case $xtype in
	file)
		vnd=$(xenstore-read "$xpath/vnd" || echo none)
		if [ $vnd != none ]; then
			vnconfig -u $vnd
		fi
		;;
	phy)
		;;
	*)
		echo "unknown type $xtype" >&2
		;;
	esac
	xenstore-rm $xpath
	exit 0
	;;
2)
	case $xtype in
	file)
		# Store the list of available vnd(4) devices in
		#``available_disks'', and mark them as ``free''.
		list=`ls -1 /dev/vnd[0-9]*d | sed "s,/dev/vnd,,;s,d,," | sort -n`
		for i in $list; do
			disk="vnd$i"
			available_disks="$available_disks $disk"
			eval $disk=free
		done
		claim_lock block
		# Mark the used vnd(4) devices as ``used''.
		for disk in `sysctl hw.disknames`; do
			case $disk in
			vnd[0-9]*) eval $disk=used ;;
			esac
		done
		# Configure the first free vnd(4) device.
		for disk in $available_disks; do
			eval status=\$$disk
			if [ "$status" = "free" ] && \
			    vnconfig /dev/${disk}d $xparams >/dev/null; then
				device=/dev/${disk}d
				break	
			fi
		done
		release_lock block
		if [ x$device = x ] ; then
			error "no available vnd device"
		fi
		xenstore-write $xpath/vnd $device
		;;
	phy)
		device=$xparams
		;;
	esac
	physical_device=$(stat -f '%r' "$device")
	xenstore-write $xpath/physical-device $physical_device
	xenstore-write $xpath/hotplug-status connected
	exit 0
	;;
*)
	exit 0
	;;
esac