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#!/bin/sh
die() { printf "%s: Error: %s\n" "$0" "$*" >&2; exit 1; }
[ "$(id -u)" = 0 ] || die 'you are not root'
shrink()
{
local shrinkmegs=100 mountpoint="$1"
while true; do
while ! btrfs filesystem resize -${shrinkmegs}M "$mountpoint"/; do
shrinkmegs=$((shrinkmegs - 10 ))
if [ $shrinkmegs -lt 10 ]; then
return
fi
done
done
}
btrfs_truncate()
{
local img="$1" bytes
# 548044800/1176715264 bytes used
bytes=$(file "$img" | sed -ne 's?.*/\([0-9]*\) bytes used.*?\1?p')
if [ "$bytes" ]; then
truncate -s "$bytes" "$img"
fi
}
main()
{
if [ -d "$1" ]; then
mountpoint=$1
mountpoint -q "$mountpoint" || die "not a mountpoint: $1"
shrink "$mountpoint"
elif [ -f "$1" ]; then
mountpoint="$1".mnt.tmp
mkdir "$mountpoint"
mount -t btrfs "$1" "$mountpoint"
result=$?
if [ $result = 0 ]; then
shrink "$mountpoint"
result=$?
umount "$mountpoint"
fi
rmdir "$mountpoint"
btrfs_truncate "$1"
return $result
else
die "not a file or directory: $1"
fi
}
main "$@"
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