core-admin/qubes-rpc/admin.vm.volume.Import

#!/bin/sh
#
# This Admin API call is implemented as a custom script, instead of dumb
# passthrough to qubesd because it may get huge amount of data (whole root.img
# for example). qubesd cannot handle it because:
#  1. It loads the whole payload into memory, before even start looking at it
#     (and later, do not allow to modify/append it).
#  2. There is 64kB limit on payload size that qubesd can handle (because of
#     point 1).
#  3. Performance reasons (qubesd is not optimized for performance, passing
#     such large data stream through it would take ages).
#
# The whole admin.vm.volume.Import consists of:
#    1. Permissions checks, getting a path from appropriate storage pool (done
#       by qubesd)
#    2. Actual data import (done by this script, using dd)
#    3. Report final result, produce final response to the caller (done by
#       qubesd)
#    
#    This way we do not pass all the data through qubesd, but still can
#    control the process from there in a meaningful way. Note that the last
#    part (second call to qubesd) may perform all kind of verification (like
#    a signature check on the data, or so) and can also prevent VM from
#    starting (hooking also domain-pre-start event) from not verified image.

set -e

# use temporary file, because env variables deal poorly with \0 inside
tmpfile=$(mktemp)
trap "rm -f $tmpfile" EXIT
qubesd-query -e \
        "$QREXEC_REMOTE_DOMAIN" \
        "admin.vm.volume.Import" \
        "$QREXEC_REQUESTED_TARGET" \
        "$1" >$tmpfile

# exit if qubesd returned an error (not '0\0')
if [ "$(head -c 2 $tmpfile | xxd -p)" != "3000" ]; then
    cat "$tmpfile"
    exit 1
fi
size=$(tail -c +3 "$tmpfile"|cut -d ' ' -f 1)
path=$(tail -c +3 "$tmpfile"|cut -d ' ' -f 2)

# now process stdin into this path
if sudo dd bs=4k of="$path" count="$size" iflag=count_bytes,fullblock \
        conv=sparse,notrunc,nocreat,fdatasync status=none; then
    status="ok"
else
    status="fail"
fi

# send status notification to qubesd, and pass its response to the caller
echo -n "$status" | qubesd-query -c /var/run/qubesd.internal.sock \
    "$QREXEC_REMOTE_DOMAIN" \
    "internal.vm.volume.ImportEnd" \
    "$QREXEC_REQUESTED_TARGET" \
    "$1"