locked hotplug scripts

[Christoph Badura <bad%bsd.de@localhost>]

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.

--chris

Attachment: locking.sh
Description: Bourne shell script

#!/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 \
	               $xpath/hotplug-error "$@"
	release_lock block
	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 $xtype in
	file)
		claim_lock block
		vnd=$(xenstore-read "$xpath/vnd" || echo none)
		if [ $vnd != none ]; then
			vnconfig -u $vnd
		fi
		release_lock block
		;;
	phy)
		;;
	*)
		echo "unknown type $xtype" >&2
		;;
	esac
	xenstore-rm $xpath
	exit 0
	;;
2)
	claim_lock block
	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
		# 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
		if [ x$device = x ] ; then
			release_lock block
			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
	release_lock block
	exit 0
	;;
*)
	exit 0
	;;
esac