[PATCH] NetBSD hotplug: Introduce locking functions

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

From: Manuel Bouyer <bouyer@netbsd.org>

On NetBSD, some block device configuration requires serialisation.
Introcuce locking functions, and use them in the block script where
appropriate.

Signed-off-by: Manuel Bouyer <bouyer@netbsd.org>
---
 tools/hotplug/NetBSD/Makefile   |  1 +
 tools/hotplug/NetBSD/block      |  5 ++-
 tools/hotplug/NetBSD/locking.sh | 72 +++++++++++++++++++++++++++++++++
 3 files changed, 77 insertions(+), 1 deletion(-)
 create mode 100644 tools/hotplug/NetBSD/locking.sh

diff --git a/tools/hotplug/NetBSD/Makefile b/tools/hotplug/NetBSD/Makefile
index 6926885ab8..114b223207 100644
--- a/tools/hotplug/NetBSD/Makefile
+++ b/tools/hotplug/NetBSD/Makefile
@@ -3,6 +3,7 @@ include $(XEN_ROOT)/tools/Rules.mk
 
 # Xen script dir and scripts to go there.
 XEN_SCRIPTS =
+XEN_SCRIPTS += locking.sh
 XEN_SCRIPTS += block
 XEN_SCRIPTS += vif-bridge
 XEN_SCRIPTS += vif-ip
diff --git a/tools/hotplug/NetBSD/block b/tools/hotplug/NetBSD/block
index 32c20b6c89..23c8e38ebf 100644
--- a/tools/hotplug/NetBSD/block
+++ b/tools/hotplug/NetBSD/block
@@ -6,6 +6,7 @@
 
 DIR=$(dirname "$0")
 . "${DIR}/hotplugpath.sh"
+. "${DIR}/locking.sh"
 
 PATH=${bindir}:${sbindir}:${LIBEXEC_BIN}:/bin:/usr/bin:/sbin:/usr/sbin
 export PATH
@@ -62,6 +63,7 @@ case $xstatus in
 			available_disks="$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
@@ -77,6 +79,7 @@ case $xstatus in
 				break	
 			fi
 		done
+		release_lock block
 		if [ x$device = x ] ; then
 			error "no available vnd device"
 		fi
@@ -86,7 +89,7 @@ case $xstatus in
 		device=$xparams
 		;;
 	esac
-	physical_device=$(stat -f '%r' "$device")
+	physical_device=$(stat -L -f '%r' "$device")
 	xenstore-write $xpath/physical-device $physical_device
 	xenstore-write $xpath/hotplug-status connected
 	exit 0
diff --git a/tools/hotplug/NetBSD/locking.sh b/tools/hotplug/NetBSD/locking.sh
new file mode 100644
index 0000000000..88257f62b7
--- /dev/null
+++ b/tools/hotplug/NetBSD/locking.sh
@@ -0,0 +1,72 @@
+#!/bin/sh
+#
+# Copyright (c) 2016, Christoph Badura.  All rights reserved.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions
+# are met:
+# 1. Redistributions of source code must retain the above copyright
+#    notice, this list of conditions and the following disclaimer.
+# 2. Redistributions in binary form must reproduce the above copyright
+#    notice, this list of conditions and the following disclaimer in the
+#    documentation and/or other materials provided with the distribution.
+#
+# THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS
+# OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+# DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT,
+# INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
+# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
+# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+#
+
+LOCK_BASEDIR="$XEN_LOCK_DIR/xen-hotplug"
+
+_lockfd=9
+_have_lock=0	# lock not taken yet.
+
+SHLOCK="shlock ${_shlock_debug-}"
+
+_lock_set_vars() {
+	_lockfile="$LOCK_BASEDIR/$1.lock"
+	_lockfifo="$LOCK_BASEDIR/$1.fifo"
+}
+
+_lock_init() {
+	mkdir -p "$LOCK_BASEDIR" 2>/dev/null || true
+	mkfifo $_lockfifo 2>/dev/null || true
+}
+
+#
+# use a named pipe as condition variable
+# opening for read-only blocks when there's no writer.
+# opening for read-write never blocks but unblocks any waiting readers.
+# 
+_lock_wait_cv() {
+	eval "exec $_lockfd<  $_lockfifo ; exec $_lockfd<&-"
+}
+_lock_signal_cv() {
+	eval "exec $_lockfd<> $_lockfifo ; exec $_lockfd<&-"
+}
+
+claim_lock() {
+	_lock_set_vars $1
+	_lock_init
+	until $SHLOCK -f $_lockfile -p $$; do
+		_lock_wait_cv
+	done
+	_have_lock=1
+	# be sure to release the lock when the shell exits
+	trap "release_lock $1" 0 1 2 15
+}
+
+release_lock() {
+	_lock_set_vars $1
+	[ "$_have_lock" != 0 -a -f $_lockfile ] && rm $_lockfile
+	_have_lock=0
+	_lock_signal_cv;
+}
-- 
2.29.2