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|
#!/bin/sh
#
# Copyright (c) 2008 Silicon Graphics, Inc. All Rights Reserved.
#
# This program is free software; you can redistribute it and/or modify it
# under the terms of the GNU General Public License as published by the
# Free Software Foundation; either version 2 of the License, or (at your
# option) any later version.
#
# This program is distributed in the hope that it will be useful, but
# WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
# or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
# for more details.
#
# Replace a subtree in a performance metrics namespace (PMNS) with a new
# subtree read from a file. The file is moved (note: not copied) into the
# PMNS and given the same name as the subtree.
#
# Usage: ReplacePmnsSubtree [-n namespace] pmns-subtree replacement-file
#
# Refer to the NOTE at the bottom of the file for important locking details.
#
. $PCP_DIR/etc/pcp.env
namespace=$PCP_VAR_DIR/pmns/root
# Print usage message to stderr and exit with status provided (default 1)
usageExit()
{
echo "Usage: $prog [-n namespace] pmns-subtree replacement-file" 1>&2
exit ${1:-1}
}
# Sanity check options, parameters, namespace, etc.
prog=`basename $0`
while getopts n:\? c
do
case "$c" in
n)
if [ "x$OPTARG" = x ]
then
echo "$prog: -n requires a namespace" 1>&2
exit 1
else
namespace="$OPTARG"
fi
;;
\?)
usageExit 0
;;
esac
done
if [ ! -f $namespace ]
then
echo "$prog: namespace doesn't exist: $namespace" 1>&2
exit 1
fi
[ $# != 2 ] && usageExit
subtree=$1
newSubtreeFile=$2
namespaceDir=`dirname $namespace`
if [ ! -w $namespaceDir ]
then
echo "$prog: can't write namespace directory $namespaceDir" 1>&2
exit 1
fi
if [ ! -f $newSubtreeFile ]
then
echo "$prog: can't read replacement namespace subtree file for $subtree:" \
"$newSubtreeFile" 1>&2
exit 1
fi
# variables for back-up/restore of namespace files affected by this script
backups="root"
[ -f "$namespaceDir/$subtree" ] && backups="$backups $subtree"
backSuffix="$prog-$$-backup"
restore=false # restore backup namespace files in cleanup()
# Signal and exit handler to clean/restore namespace (lock and backups).
haveLock=false
# signals we need to be careful of ... HUP, INT, QUIT, PIPE, ALRM, TERM
#
STD_SIGNALS="1 2 3 13 14 15"
cleanup()
{
# Release namespace lock as early as possible. Ignore signals to avoid
# releasing a lock already released.
trap "" $STD_SIGNALS
if $restore
then
for f in $backups
do
[ -f "$namespaceDir/.$f-$backSuffix" ] && \
mv "$namespaceDir/.$f-$backSuffix" "$namespaceDir/$f"
done
$haveLock && unlockpmns $namespace
haveLock=false
else
$haveLock && unlockpmns $namespace
haveLock=false
for f in $backups
do
rm -f "$namespaceDir/.$f-$backSuffix"
done
fi
}
trap "cleanup; exit" 0 $STD_SIGNALS
# "haveLock=true" is duplicated in both "if" and "else" to minimise the window
# for a signal leaving an orphaned lock if the "else" condition fires (we
# stole an existing lock). See note at bottom of script for details.
if lockpmns $namespace
then
haveLock=true # duplicate: minimise race condition (see note above)
else
haveLock=true # duplicate: minimise race condition (see note above)
$PCP_BINADM_DIR/pmpost "PCP: PMNS lock stolen by: $*"
fi
# Namespace is locked, back up affected files. Once backup completes, enable
# namespace restore during error handling.
backupErr=false
for f in $backups
do
dest="$namespaceDir/.$f-$backSuffix"
if cp "$namespaceDir/$f" "$dest"
then
:
else
echo "error creating namespace backup for $f" 1>&2
backupErr=true
fi
done
$backupErr && exit 1
restore=true
# pmnsdel leaves any file corresponding to the deleted subtree in place after
# it runs, regardless of whether it succeeds or fails. Allow pmnsdel to fail
# (there may be no existing subtree). Return 0 only if the entire replacement
# succeeds.
sts=0
pmnsdel -n $namespace $subtree >/dev/null 2>&1
if pmnsadd -n $namespace $newSubtreeFile >/dev/null 2>&1
then
mv -f $newSubtreeFile $namespaceDir/$subtree
sts=$?
else
sts=1
fi
[ $sts = 0 ] && restore=false
exit $sts
##############################################################################
# NOTE
#
# If a signal occurs in the very short window between pmnslock returning and
# setting haveLock, the lock is not released by cleanup(). Any subsequent
# process calling pmnslock will block until its pmnslock steals the lock
# (currently after 120 secs). That window is carefully minimised.
#
# Past versions of similar scripts (e.g. Rebuild) unconditionally unlocked the
# namespace when a signal was caught. This could potentially happen while
# still waiting to acquire the lock, breaking a lock held by another process!
#
# Consider locking and backup/restore implications carefully if making changes.
|
