xen/tools/examples/block

#!/bin/sh

set -x

dir=$(dirname "$0")
. "$dir/block-common.sh"

expand_dev() {
  local dev
  case $1 in
  /*)
    dev=$1
    ;;
  *)
    dev=/dev/$1
    ;;
  esac
  echo -n $dev
}


canonicalise_mode()
{
  local mode="$1"

  if ! expr index "$mode" 'w' >/dev/null
  then
    echo 'ro'
  elif ! expr index "$mode" '!' >/dev/null
  then
    echo 'rw'
  else
    echo 'no'
  fi
}


##
# check_sharing device device_major_minor mode
#
# Check whether the device requested is already in use.  To use the device in
# read-only mode, it may be in use in read-only mode, but may not be in use in
# read-write anywhere at all.  To use the device in read-write mode, it must
# not be in use anywhere at all.
#
check_sharing()
{
  local dev="$1"
  local mode="$2"

  local devmm=$(device_major_minor "$dev")
  local file

  if [ "$mode" == 'rw' ]
  then
    toskip="^$"
  else
    toskip="^[^ ]* [^ ]* [^ ]* ro "
  fi

  for file in $(cat /proc/mounts | grep -v "$toskip" | cut -f 1 -d ' ')
  do
    if [ -e "$file" ]
    then
      local d=$(device_major_minor "$file")

      if [ "$d" == "$devmm" ]
      then
        echo 'local'
        return
      fi
    fi
  done

  for file in /sys/devices/xen-backend/*/physical_device
  do
    if [ -e "$file" ] # Cope with no devices, i.e. the * above did not expand.
    then
      local d=$(cat "$file")
      if [ "$d" == "$devmm" ]
      then
        if [ "$mode" == 'rw' ]
        then
          echo 'guest'
          return
        else
          local m=$(cat "${file/physical_device/mode}")

          if expr index "$m" 'w' >/dev/null
          then
            echo 'guest'
            return
          fi
        fi
      fi
    fi
  done

  echo 'ok'
}


check_device_sharing()
{
  local dev="$1"
  local mode=$(canonicalise_mode "$2")
  local result

  if [ "$mode" == 'no' ]
  then
    return 0
  fi

  result=$(check_sharing "$dev" "$mode")

  if [ "$result" != 'ok' ]
  then
    do_ebusy "Device $dev is mounted " "$mode" "$result"
  fi
}


check_file_sharing()
{
  local file="$1"
  local dev="$2"
  local mode="$3"

  result=$(check_sharing "$dev" "$mode")

  if [ "$result" != 'ok' ]
  then
    do_ebusy "File $file is loopback-mounted through $dev,
which is mounted " "$mode" "$result"
  fi
}


do_ebusy()
{
  local prefix="$1"
  local mode="$2"
  local result="$3"

  if [ "$result" == 'guest' ]
  then
    dom='a guest '
    when='now'
  else
    dom='the privileged '
    when='by a guest'
  fi

  if [ "$mode" == 'rw' ]
  then
    m1=''
    m2=''
  else
    m1='read-write '
    m2='read-only '
  fi

  ebusy \
"${prefix}${m1}in ${dom}domain,
and so cannot be mounted ${m2}${when}."
}


t=$(xenstore_read_default "$XENBUS_PATH/type" 'MISSING')

case "$command" in
  add)
    phys=$(xenstore_read_default "$XENBUS_PATH/physical-device" 'MISSING')
    if [ "$phys" != 'MISSING' ]
    then
      # Depending upon the hotplug configuration, it is possible for this
      # script to be called twice, so just bail.
      exit 0
    fi

    p=$(xenstore_read "$XENBUS_PATH/params")
    mode=$(xenstore_read "$XENBUS_PATH/mode")

    case $t in 
      phy)
        dev=$(expand_dev $p)
        check_device_sharing "$dev" "$mode"
	write_dev "$dev"
	exit 0
	;;

      file)
        # Canonicalise the file, for sharing check comparison, and the mode
        # for ease of use here.
        file=$(readlink -f "$p")
        mode=$(canonicalise_mode "$mode")

        if [ "$mode" == 'rw' ] && ! stat "$file" -c %A | grep w >&/dev/null
        then
          ebusy \
"File $file is read-only, and so I will not
mount it read-write in a guest domain."
        fi


	while true
        do 
          loopdev=''
          for dev in /dev/loop*
          do
            if [ ! -b "$dev" ]
            then
              continue
            fi

            f=$(losetup "$dev" 2>/dev/null) || f='()'
            f=$(echo "$f" | sed -e 's/.*(\(.*\)).*/\1/g')

            log err "$file $f $dev"

            if [ "$f" ]
            then
              # $dev is in use.  Check sharing.
              if [ "$mode" == 'no' ]
              then
                continue
              fi

              f=$(readlink -f "$f")

              if [ "$f" == "$file" ]
              then
                check_file_sharing "$file" "$dev" "$mode"
              fi
            else
              # $dev is not in use, so we'll remember it for use later; we want
              # to finish the sharing check first.
              
              if [ "$loopdev" == '' ]
              then
                loopdev="$dev"
              fi
            fi
          done

          if [ "$loopdev" == '' ]
          then
            fatal 'Failed to find an unused loop device'
          fi
          if losetup "$loopdev" "$file"
          then
	    log err "mapped $file using $loopdev"
            xenstore_write "$XENBUS_PATH/node" "$loopdev"
            write_dev "$loopdev"
            exit 0
          else
            log err "losetup $loopdev $file failed, retry"
          fi
	done
	;;
    esac
    ;;

  remove)
    case $t in 
      phy)
	exit 0
	;;

      file)
        node=$(xenstore_read "$XENBUS_PATH/node")
	losetup -d "$node"
	exit 0
	;;
    esac
    ;;

esac

# If we've reached here, $t is neither phy nor file, so fire a helper script.
[ -x /etc/xen/scripts/block-"$t" ] && \
  /etc/xen/scripts/block-"$t" "$command" $node