72 lines
2.2 KiB
Bash
72 lines
2.2 KiB
Bash
#!/bin/sh
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#
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# Copyright (c) 2016, Christoph Badura. All rights reserved.
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#
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# Redistribution and use in source and binary forms, with or without
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# modification, are permitted provided that the following conditions
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# are met:
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# 1. Redistributions of source code must retain the above copyright
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# notice, this list of conditions and the following disclaimer.
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# 2. Redistributions in binary form must reproduce the above copyright
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# notice, this list of conditions and the following disclaimer in the
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# documentation and/or other materials provided with the distribution.
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#
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# THIS SOFTWARE IS PROVIDED BY THE AUTHOR(S) ``AS IS'' AND ANY EXPRESS
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# OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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# WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
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# DISCLAIMED. IN NO EVENT SHALL THE AUTHOR(S) BE LIABLE FOR ANY DIRECT,
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# INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
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# (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
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# SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
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# CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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# LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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# OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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# SUCH DAMAGE.
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#
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LOCK_BASEDIR="$XEN_LOCK_DIR/xen-hotplug"
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_lockfd=9
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_have_lock=0 # lock not taken yet.
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SHLOCK="shlock ${_shlock_debug-}"
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_lock_set_vars() {
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_lockfile="$LOCK_BASEDIR/$1.lock"
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_lockfifo="$LOCK_BASEDIR/$1.fifo"
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}
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_lock_init() {
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mkdir -p "$LOCK_BASEDIR" 2>/dev/null || true
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mkfifo $_lockfifo 2>/dev/null || true
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}
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#
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# use a named pipe as condition variable
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# opening for read-only blocks when there's no writer.
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# opening for read-write never blocks but unblocks any waiting readers.
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#
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_lock_wait_cv() {
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eval "exec $_lockfd< $_lockfifo ; exec $_lockfd<&-"
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}
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_lock_signal_cv() {
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eval "exec $_lockfd<> $_lockfifo ; exec $_lockfd<&-"
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}
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claim_lock() {
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_lock_set_vars $1
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_lock_init
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until $SHLOCK -f $_lockfile -p $$; do
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_lock_wait_cv
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done
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_have_lock=1
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# be sure to release the lock when the shell exits
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trap "release_lock $1" 0 1 2 15
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}
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release_lock() {
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_lock_set_vars $1
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[ "$_have_lock" != 0 -a -f $_lockfile ] && rm $_lockfile
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_have_lock=0
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_lock_signal_cv;
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}
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