diff options
Diffstat (limited to 'extensions/recv-hole')
-rwxr-xr-x | extensions/recv-hole | 158 |
1 files changed, 158 insertions, 0 deletions
diff --git a/extensions/recv-hole b/extensions/recv-hole new file mode 100755 index 00000000..fe69f304 --- /dev/null +++ b/extensions/recv-hole @@ -0,0 +1,158 @@ +#!/bin/sh +# +# Copyright (C) 2014-2015 Codethink Limited +# +# 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; version 2 of the License. +# +# 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. +# +# You should have received a copy of the GNU General Public License along +# with this program. If not, see <http://www.gnu.org/licenses/>. +# +# =*= License: GPL-2 =*= + + +# Receive a data stream describing a sparse file, and reproduce it, +# either to a named file or stdout. +# +# The data stream is simple: it's a sequence of DATA or HOLE records: +# +# DATA +# 123 +# <123 bytes of binary data, NOT including newline at the end> +# +# HOLE +# 123 +# +# This shell script can be executed over ssh (given to ssh as an arguemnt, +# with suitable escaping) on a different computer. This allows a large +# sparse file (e.g., disk image) be transferred quickly. +# +# This script should be called in one of the following ways: +# +# recv-hole file FILENAME +# recv-hole vbox FILENAME DISKSIZE +# +# In both cases, FILENAME is the pathname of the disk image on the +# receiving end. DISKSIZE is the size of the disk image in bytes. The +# first form is used when transferring a disk image to become an +# identical file on the receiving end. +# +# The second form is used when the disk image should be converted for +# use by VirtualBox. In this case, we want to avoid writing a +# temporary file on disk, and then calling the VirtualBox VBoxManage +# tool to do the conversion, since that would involve large amounts of +# unnecessary I/O and disk usage. Instead we pipe the file directly to +# VBoxManage, avoiding those issues. The piping is done here in this +# script, instead of in the caller, to make it easier to run things +# over ssh. +# +# However, since it's not possible seek in a Unix pipe, we have to +# explicitly write the zeroes into the pipe. This is not +# super-efficient, but the way to avoid that would be to avoid sending +# a sparse file, and do the conversion to a VDI on the sending end. +# That is out of scope for xfer-hole and recv-hole. + + +set -eu + + +die() +{ + echo "$@" 1>&2 + exit 1 +} + + +recv_hole_to_file() +{ + local n + + read n + truncate --size "+$n" "$1" +} + + +recv_data_to_file() +{ + local n + read n + + local blocksize=1048576 + local blocks=$(($n / $blocksize)) + local extra=$(($n % $blocksize)) + + xfer_data_to_stdout "$blocksize" "$blocks" >> "$1" + xfer_data_to_stdout 1 "$extra" >> "$1" +} + + +recv_hole_to_stdout() +{ + local n + read n + (echo "$n"; cat /dev/zero) | recv_data_to_stdout +} + + +recv_data_to_stdout() +{ + local n + read n + + local blocksize=1048576 + local blocks=$(($n / $blocksize)) + local extra=$(($n % $blocksize)) + + xfer_data_to_stdout "$blocksize" "$blocks" + xfer_data_to_stdout 1 "$extra" +} + + +xfer_data_to_stdout() +{ + local log="$(mktemp)" + if ! dd "bs=$1" count="$2" iflag=fullblock status=noxfer 2> "$log" + then + cat "$log" 1>&2 + rm -f "$log" + exit 1 + else + rm -f "$log" + fi +} + + +type="$1" +case "$type" in + file) + output="$2" + truncate --size=0 "$output" + while read what + do + case "$what" in + DATA) recv_data_to_file "$output" ;; + HOLE) recv_hole_to_file "$output" ;; + *) die "Unknown instruction: $what" ;; + esac + done + ;; + vbox) + output="$2" + disk_size="$3" + while read what + do + case "$what" in + DATA) recv_data_to_stdout ;; + HOLE) recv_hole_to_stdout ;; + *) die "Unknown instruction: $what" ;; + esac + done | + VBoxManage convertfromraw stdin "$output" "$disk_size" + ;; +esac |