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#!/bin/sh
set -e
imgloop=
tmpfile=
tmploop=
dmname=
cowlink=
function cleanup () {
set +e
[ -n "$cowlink" ] && rm $cowlink
[ -n "$dmname" ] && dmsetup remove $dmname
[ -n "$tmploop" ] && losetup -d $tmploop
[ -n "$tmpfile" ] && rm $tmpfile
[ -n "$imgloop" ] && losetup -d $imgloop
}
trap cleanup EXIT
imgfile=$1 ; shift
command=$1 ; shift
if [ -z "$imgfile" -o -z "$command" ] ; then
echo Syntax: $0 /path/to/image/file command [args..]
exit 1
fi
# Set up image loop device
x=`losetup -f` ; losetup -r $x $imgfile ; imgloop=$x
# Create temporary file and set up temporary loop device
tmpfile=`mktemp $imgfile.XXXXXXXXXX`
truncate -r $imgfile $tmpfile
x=`losetup -f` ; losetup $x $tmpfile ; tmploop=$x
# Create snapshot device
imgsize=`blockdev --getsz $imgloop`
x=`basename $imgfile` ; echo 0 $imgsize snapshot $imgloop $tmploop N 16 | \
dmsetup create $x ; dmname=$x
chown --reference=$imgfile /dev/mapper/$dmname
chmod --reference=$imgfile /dev/mapper/$dmname
# Create symlink
x=$imgfile.cow ; ln -s /dev/mapper/$dmname $x ; cowlink=$x
# Wait until killed
echo "Created $cowlink"
$command "$@" $cowlink
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