Mailing List Archive

# HG changeset patch
# User emellor@leeni.uk.xensource.com
# Node ID a57cccdf2d6d5c70bef4f570fe2f906fd18ba406
# Parent d581e11e247c72ac48ae5be69fd5c08a823dd655
Added serialisation facilities. Udev is supposed to serialise events, but sadly
the older hotplug infrastructure does not, so we must be able to serialise the
block-sharing checks (etc) ourselves.

Redirect stderr to /var/log/xen-hotplug.log, for better debugging.

Signed-off-by: Ewan Mellor <ewan@xensource.com>

diff -r d581e11e247c -r a57cccdf2d6d tools/examples/xen-hotplug-common.sh
--- a/tools/examples/xen-hotplug-common.sh Fri Dec 2 15:36:39 2005
+++ b/tools/examples/xen-hotplug-common.sh Fri Dec 2 15:38:22 2005
@@ -18,6 +18,8 @@

dir=$(dirname "$0")
. "$dir/xen-script-common.sh"
+
+exec 2>>/var/log/xen-hotplug.log

export PATH="/sbin:/bin:/usr/bin:/usr/sbin:$PATH"
export LANG="POSIX"
@@ -45,7 +47,7 @@
}

sigerr() {
- fatal "$0" "$@" "failed; error detected."
+ fatal "$0 failed; error detected."
}

trap sigerr ERR
@@ -86,4 +88,88 @@
xenstore-write "$@" || fatal "Writing $@ to xenstore failed."
}

+
+#
+# Serialisation
+#
+
+LOCK_SLEEPTIME=1
+LOCK_SPINNING_RETRIES=5
+LOCK_RETRIES=10
+LOCK_BASEDIR=/var/run/xen-hotplug
+
+
+claim_lock()
+{
+ local lockdir="$LOCK_BASEDIR/$1"
+ mkdir -p "$LOCK_BASEDIR"
+ _claim_lock "$lockdir"
+}
+
+
+release_lock()
+{
+ _release_lock "$LOCK_BASEDIR/$1"
+}
+
+
+_claim_lock()
+{
+ local lockdir="$1"
+ local owner=$(_lock_owner "$lockdir")
+ local retries=0
+
+ while expr $retries '<' $LOCK_RETRIES
+ do
+ mkdir "$lockdir" && trap "release_lock $1; sigerr" ERR &&
+ _update_lock_info "$lockdir" && return
+
+ local new_owner=$(_lock_owner "$lockdir")
+ if [ "$new_owner" != "$owner" ]
+ then
+ owner="$new_owner"
+ retries=0
+ fi
+
+ if expr $retries '>' $LOCK_SPINNING_RETRIES
+ then
+ sleep $LOCK_SLEEPTIME
+ else
+ sleep 0
+ fi
+ retries=$(($retries + 1))
+ done
+ _steal_lock "$lockdir"
+}
+
+
+_release_lock()
+{
+ trap sigerr ERR
+ rm -rf "$1" || true
+}
+
+
+_steal_lock()
+{
+ local lockdir="$1"
+ local owner=$(cat "$lockdir/owner" 2>/dev/null || echo "unknown")
+ log err "Forced to steal lock on $lockdir from $owner!"
+ _release_lock "$lockdir"
+ _claim_lock "$lockdir"
+}
+
+
+_lock_owner()
+{
+ cat "$1/owner" 2>/dev/null || echo "unknown"
+}
+
+
+_update_lock_info()
+{
+ echo "$$: $0" >"$1/owner"
+}
+
+
log debug "$@" "XENBUS_PATH=$XENBUS_PATH"

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