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111 lines
2.2 KiB
111 lines
2.2 KiB
#
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# Copyright (c) 2005 XenSource Ltd.
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#
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# This library is free software; you can redistribute it and/or
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# modify it under the terms of version 2.1 of the GNU Lesser General Public
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# License as published by the Free Software Foundation.
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#
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# This library is distributed in the hope that it will be useful,
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# but WITHOUT ANY WARRANTY; without even the implied warranty of
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# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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# Lesser General Public License for more details.
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#
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# You should have received a copy of the GNU Lesser General Public
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# License along with this library; if not, write to the Free Software
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# Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
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#
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#
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# Serialisation
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#
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LOCK_SLEEPTIME=1
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LOCK_SPINNING_RETRIES=5
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LOCK_RETRIES=100
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LOCK_BASEDIR=/var/run/xen-hotplug
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claim_lock()
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{
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local lockdir="$LOCK_BASEDIR/$1"
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mkdir -p "$LOCK_BASEDIR"
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_claim_lock "$lockdir"
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}
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release_lock()
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{
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_release_lock "$LOCK_BASEDIR/$1"
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}
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# This function will be redefined in xen-hotplug-common.sh.
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sigerr() {
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exit 1
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}
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_claim_lock()
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{
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local lockdir="$1"
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local owner=$(_lock_owner "$lockdir")
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local retries=0
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while [ $retries -lt $LOCK_RETRIES ]
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do
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mkdir "$lockdir" 2>/dev/null && trap "_release_lock $lockdir; sigerr" ERR &&
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_update_lock_info "$lockdir" && return
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local new_owner=$(_lock_owner "$lockdir")
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if [ "$new_owner" != "$owner" ]
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then
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owner="$new_owner"
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retries=0
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else
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local pid=$(echo $owner | cut -d : -f 1)
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if [ -n "$pid" -a "$pid" != "unknown" -a ! -f "/proc/$pid/status" ]
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then
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_release_lock $lockdir
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fi
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fi
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if [ $retries -gt $LOCK_SPINNING_RETRIES ]
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then
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sleep $LOCK_SLEEPTIME
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else
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sleep 0
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fi
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retries=$(($retries + 1))
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done
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_steal_lock "$lockdir"
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}
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_release_lock()
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{
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trap sigerr ERR
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rm -rf "$1" 2>/dev/null || true
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}
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_steal_lock()
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{
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local lockdir="$1"
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local owner=$(cat "$lockdir/owner" 2>/dev/null || echo "unknown")
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log err "Forced to steal lock on $lockdir from $owner!"
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_release_lock "$lockdir"
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_claim_lock "$lockdir"
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}
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_lock_owner()
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{
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cat "$1/owner" 2>/dev/null || echo "unknown"
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}
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_update_lock_info()
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{
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echo "$$: $0" >"$1/owner"
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}
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