[PATCH] NetBSD hotplug: Introduce locking functions

[Manuel Bouyer <bouyer@xxxxxxxxxxxxxxx>]

From: Manuel Bouyer <bouyer@xxxxxxxxxx>

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@xxxxxxxxxx>
---
 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