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Diffstat (limited to 'src/pmns/ReplacePmnsSubtree')
| -rw-r--r-- | src/pmns/ReplacePmnsSubtree | 184 |
1 files changed, 184 insertions, 0 deletions
diff --git a/src/pmns/ReplacePmnsSubtree b/src/pmns/ReplacePmnsSubtree new file mode 100644 index 0000000..8b5a05c --- /dev/null +++ b/src/pmns/ReplacePmnsSubtree @@ -0,0 +1,184 @@ +#!/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. |