XEN: различия между версиями

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(не показано 17 промежуточных версий 2 участников)
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'''Здесь все что касается XEN'''
'''Здесь все что касается XEN'''
<hr>
 
*[[Опции доменов Xen]] - описание параметров файлов виртуальных машин Xen (доменов DomU)
*[http://www.meadowcourt.org/downloads/ Драйверы]
----
* [http://bits.xensource.com/oss-xen/release/4.3.0/xen-4.3.0.tar.gz Исходники XEN-4.3]
* [http://hyper-choi.blogspot.ru/2013/06/xen-43-rc1-installation.html Сборка XEN-4.3]
* [http://wiki.xen.org/wiki/Compiling_Xen_From_Source#Build_Dependencies Compiling Xen From Source]
----
 
* [[Сборка Xen 4.2 в Debian Wheezy и проброс устройств в гипервизор Xen]]
* [[Сборка Xen 4.2 в Debian Wheezy и проброс устройств в гипервизор Xen]]
* [[Xen 4.2.x Сборка пакета deb для Wheezy]]  - upstream
* [[Установка Xen 4.1 на Debian Squeeze]]
* [[Установка Xen 4.1 на Debian Squeeze]]


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* [http://xgu.ru/wiki/%D0%A1%D1%80%D0%B5%D0%B4%D1%81%D1%82%D0%B2%D0%B0_%D1%83%D0%BF%D1%80%D0%B0%D0%B2%D0%BB%D0%B5%D0%BD%D0%B8%D1%8F_Xen Средства_управления_Xen]
* [http://xgu.ru/wiki/%D0%A1%D1%80%D0%B5%D0%B4%D1%81%D1%82%D0%B2%D0%B0_%D1%83%D0%BF%D1%80%D0%B0%D0%B2%D0%BB%D0%B5%D0%BD%D0%B8%D1%8F_Xen Средства_управления_Xen]
* [http://how-it.ru/public/root/258-xen__probros_usb_ustroistv_vnutr_hvm_virtualnoi_mashiny__windows__ili_usb_passthrough.html проброс устройств]
* [http://how-it.ru/public/root/43-ustanovka_paravirtualnyh_draiverov_v_windows_server_2008.html Установка паравиртуальных драйверов в Windows Server 2008]
Скрипт настройки XEN при обновлении Grub:
/etc/grub.d/20_linux_xen
  #! /bin/sh
  set -e
 
  # grub-mkconfig helper script.
  # Copyright (C) 2006,2007,2008,2009,2010  Free Software Foundation, Inc.
  #
  # GRUB 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, either version 3 of the License, or
  # (at your option) any later version.
  #
  # GRUB 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 GRUB.  If not, see <http://www.gnu.org/licenses/>.
 
  prefix="/usr"
  exec_prefix="${prefix}"
  datarootdir="${prefix}/share"
 
  . "${datarootdir}/grub/grub-mkconfig_lib"
 
  export TEXTDOMAIN=grub
  export TEXTDOMAINDIR="${datarootdir}/locale"
 
  CLASS="--class gnu-linux --class gnu --class os --class xen"
 
  if [ "x${GRUB_DISTRIBUTOR}" = "x" ] ; then
    OS=GNU/Linux
  else
    OS="${GRUB_DISTRIBUTOR} GNU/Linux"
    CLASS="--class $(echo ${GRUB_DISTRIBUTOR} | tr 'A-Z' 'a-z' | cut -d' ' -f1) ${CLASS}"
  fi
 
  # loop-AES arranges things so that /dev/loop/X can be our root device, but
  # the initrds that Linux uses don't like that.
  case ${GRUB_DEVICE} in
    /dev/loop/*|/dev/loop[0-9])
      GRUB_DEVICE=`losetup ${GRUB_DEVICE} | sed -e "s/^[^(]*(\([^)]\+\)).*/\1/"`
      # We can't cope with devices loop-mounted from files here.
      case ${GRUB_DEVICE} in
        /dev/*) ;;
        *) exit 0 ;;
      esac
    ;;
  esac
 
  if [ "x${GRUB_DEVICE_UUID}" = "x" ] || [ "x${GRUB_DISABLE_LINUX_UUID}" = "xtrue" ] \
      || ! test -e "/dev/disk/by-uuid/${GRUB_DEVICE_UUID}" \
      || uses_abstraction "${GRUB_DEVICE}" lvm; then
    LINUX_ROOT_DEVICE=${GRUB_DEVICE}
  else
    LINUX_ROOT_DEVICE=UUID=${GRUB_DEVICE_UUID}
  fi
 
  # Allow overriding GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT.
  if [ "${GRUB_CMDLINE_LINUX_XEN_REPLACE}" ]; then
    GRUB_CMDLINE_LINUX="${GRUB_CMDLINE_LINUX_XEN_REPLACE}"
  fi
  if [ "${GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT}" ]; then
    GRUB_CMDLINE_LINUX_DEFAULT="${GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT}"
  fi
 
  if [ "x`${grub_probe} --device ${GRUB_DEVICE} --target=fs 2>/dev/null || true`" = xbtrfs ] \
      || [ "x`stat -f --printf=%T /`" = xbtrfs ]; then
    rootsubvol="`make_system_path_relative_to_its_root /`"
    rootsubvol="${rootsubvol#/}"
    if [ "x${rootsubvol}" != x ]; then
      GRUB_CMDLINE_LINUX="rootflags=subvol=${rootsubvol} ${GRUB_CMDLINE_LINUX}"
    fi
  fi
 
  linux_entry ()
  {
    os="$1"
    version="$2"
    xen_version="$3"
    recovery="$4"
    args="$5"
    xen_args="$6"
    if ${recovery} ; then
      title="$(gettext_quoted "%s, with Xen %s and Linux %s (recovery mode)")"
    else
      title="$(gettext_quoted "%s, with Xen %s and Linux %s")"
    fi
# дополнительные опции - можно выставить самому...
    printf 'set default="0" \n'
    printf 'set timeout=5 \n'
# ------------------------------------------------
    printf "menuentry '${title}' ${CLASS} {\n" "${os}" "${xen_version}" "${version}"
    if ! ${recovery} ; then
        save_default_entry | sed -e "s/^/\t/"
    fi
 
    if [ -z "${prepare_boot_cache}" ]; then
      prepare_boot_cache="$(prepare_grub_to_access_device ${GRUB_DEVICE_BOOT} | sed -e "s/^/\t/")"
    fi
    printf '%s\n' "${prepare_boot_cache}"
    xmessage="$(gettext_printf "Loading Xen %s ..." ${xen_version})"
    lmessage="$(gettext_printf "Loading Linux %s ..." ${version})"
    cat << EOF
          echo    '$xmessage'
          multiboot      ${rel_xen_dirname}/${xen_basename} placeholder ${xen_args}
          echo    '$lmessage'
          module  ${rel_dirname}/${basename} placeholder root=${linux_root_device_thisversion} ro ${args}
  EOF
    if test -n "${initrd}" ; then
      message="$(gettext_printf "Loading initial ramdisk ...")"
      cat << EOF
          echo    '$message'
          module  ${rel_dirname}/${initrd}
  EOF
    fi
    cat << EOF
  }
  EOF
  }
 
  linux_list=`for i in /boot/vmlinu[xz]-* /vmlinu[xz]-* /boot/kernel-*; do
      if grub_file_is_not_garbage "$i"; then
          basename=$(basename $i)
          version=$(echo $basename | sed -e "s,^[^0-9]*-,,g")
          dirname=$(dirname $i)
          config=
          for j in "${dirname}/config-${version}" "${dirname}/config-${alt_version}" "/etc/kernels/kernel-config-${version}" ; do
              if test -e "${j}" ; then
                  config="${j}"
                  break
              fi
          done
          if (grep -qx "CONFIG_XEN_DOM0=y" "${config}" 2> /dev/null || grep -qx "CONFIG_XEN_PRIVILEGED_GUEST=y" "${config}" 2> /dev/null); then echo -n "$i " ; fi
      fi
      done`
  if [ "x${linux_list}" = "x" ] ; then
      exit 0
  fi
  xen_list=`for i in /boot/xen*; do
          if grub_file_is_not_garbage "$i" ; then echo -n "$i " ; fi
        done`
  prepare_boot_cache=
 
  while [ "x${xen_list}" != "x" ] ; do
      list="${linux_list}"
      current_xen=`version_find_latest $xen_list`
      xen_basename=`basename ${current_xen}`
      xen_dirname=`dirname ${current_xen}`
      rel_xen_dirname=`make_system_path_relative_to_its_root $xen_dirname`
      xen_version=`echo $xen_basename | sed -e "s,.gz$,,g;s,^xen-,,g"`
      echo "submenu \"Xen ${xen_version}\" {"
      while [ "x$list" != "x" ] ; do
          linux=`version_find_latest $list`
          echo "Found linux image: $linux" >&2
          basename=`basename $linux`
          dirname=`dirname $linux`
          rel_dirname=`make_system_path_relative_to_its_root $dirname`
          version=`echo $basename | sed -e "s,^[^0-9]*-,,g"`
          alt_version=`echo $version | sed -e "s,\.old$,,g"`
          linux_root_device_thisversion="${LINUX_ROOT_DEVICE}"
 
          initrd=
          for i in "initrd.img-${version}" "initrd-${version}.img" \
              "initrd-${version}" "initrd.img-${alt_version}" \
              "initrd-${alt_version}.img" "initrd-${alt_version}" \
              "initramfs-genkernel-${version}" \
              "initramfs-genkernel-${alt_version}" ; do
              if test -e "${dirname}/${i}" ; then
                  initrd="$i"
                  break
              fi
          done
          if test -n "${initrd}" ; then
              echo "Found initrd image: ${dirname}/${initrd}" >&2
          else
      # "UUID=" magic is parsed by initrds.  Since there's no initrd, it can't work here.
              linux_root_device_thisversion=${GRUB_DEVICE}
          fi
 
          linux_entry "${OS}" "${version}" "${xen_version}" false \
              "${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT}" "${GRUB_CMDLINE_XEN} ${GRUB_CMDLINE_XEN_DEFAULT}"
          if [ "x${GRUB_DISABLE_RECOVERY}" != "xtrue" ]; then
              linux_entry "${OS}" "${version}" "${xen_version}" true \
                  "single ${GRUB_CMDLINE_LINUX}" "${GRUB_CMDLINE_XEN}"
          fi
 
          list=`echo $list | tr ' ' '\n' | grep -vx $linux | tr '\n' ' '`
      done
      echo "}"
      xen_list=`echo $xen_list | tr ' ' '\n' | grep -vx $current_xen | tr '\n' ' '`
  done
=='''Монтирование образа хоста XEN'''==
используем утилиту losetup:
проверяем наличие свободных устройств:
losetup -a
если все свободно, монтируем сначала образ:
losetup /dev/loop5 disk.img
смотрим смещение относительно начала:
fdisk -l /dev/loop5
пример вывода:
Disk /dev/loop5: 115.3 GB, 115343360000 bytes
255 heads, 63 sectors/track, 14023 cylinders, total 225280000 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x390038ff
      Device Boot      Start        End      Blocks  Id  System
/dev/loop5p1  *          63  104872319    52436128+  7  HPFS/NTFS/exFAT
смещение для этого раздела равно 63, размер сектора 512 байт, для программного сдвига offset=63*512 (32256)
создаем устройство типа /dev/sda1 только в варианте loop с которым будем работать:
losetup -o 32256 /dev/loop6 /dev/loop5
теперь у нас аналог /dev/sda1 только устройство /dev/loop6
можно например его примонтировать:
ntfs-3g /dev/loop6 /mnt
и делать там все что угодно..
* [http://mypvn.blogspot.ru/2010/09/xen-how-to-mount-xen-image.html по теме]
* [http://how-it.ru/public/root/388-montiruem_obraz_diska_xen__nevazhno___windows_tam_vnutri_ili__nix__bez_samogo_xen.html так же по теме]
* [http://www.desktopbsd.ru/info/6233-xen-skript-montirovaniya-obraza-sistemy-img-for-centos.html пример автоматизации]
==Xen HVM guest qemu-dm USB==
Qemu-dm used for Xen HVM (fully virtualized) guests supports USB passthru of devices from dom0 to the guest. Qemu-dm emulates USB 1.1 UHCI 2-port controller, which is pretty slow and limited in features and device support. Qemu-dm USB 1.1 passthru support is in all Xen 3.x (and newer) versions.
Qemu-dm USB 1.1 passthru doesn't require any additional backend drivers in dom0 or any additional frontend drivers in the guest!
As of Xen 4.2, HVM passthru is not available via xl, only xm. Support is slated for the 4.3 release.
Usage example in /etc/xen/<guest> cfgfile:
usb = 1
usbdevice = "host:xxxx:yyyy"
You can find out the "xxxx:yyyy" part by using "lsusb" command in dom0.
You can also plug a device into a running VM using usb-add and usb-del:
    xm usb-add domain host:xxxx:yyyy
    xm usb-del domain host:xxxx:yyyy

Текущая версия от 22:18, 13 октября 2014

Здесь все что касается XEN



VBoxManage clonehd centos6.vdi centos6.img -format RAW

Скрипт настройки XEN при обновлении Grub:

/etc/grub.d/20_linux_xen
 #! /bin/sh
 set -e
 
 # grub-mkconfig helper script.
 # Copyright (C) 2006,2007,2008,2009,2010  Free Software Foundation, Inc.
 #
 # GRUB 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, either version 3 of the License, or
 # (at your option) any later version.
 #
 # GRUB 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 GRUB.  If not, see <http://www.gnu.org/licenses/>.
 
 prefix="/usr"
 exec_prefix="${prefix}"
 datarootdir="${prefix}/share"
 
 . "${datarootdir}/grub/grub-mkconfig_lib"
 
 export TEXTDOMAIN=grub
 export TEXTDOMAINDIR="${datarootdir}/locale"
 
 CLASS="--class gnu-linux --class gnu --class os --class xen"
 
 if [ "x${GRUB_DISTRIBUTOR}" = "x" ] ; then
   OS=GNU/Linux
 else
   OS="${GRUB_DISTRIBUTOR} GNU/Linux"
   CLASS="--class $(echo ${GRUB_DISTRIBUTOR} | tr 'A-Z' 'a-z' | cut -d' ' -f1) ${CLASS}"
 fi
 
 # loop-AES arranges things so that /dev/loop/X can be our root device, but
 # the initrds that Linux uses don't like that.
 case ${GRUB_DEVICE} in
   /dev/loop/*|/dev/loop[0-9])
     GRUB_DEVICE=`losetup ${GRUB_DEVICE} | sed -e "s/^[^(]*(\([^)]\+\)).*/\1/"`
     # We can't cope with devices loop-mounted from files here.
     case ${GRUB_DEVICE} in
       /dev/*) ;;
       *) exit 0 ;;
     esac
   ;;
 esac
 
 if [ "x${GRUB_DEVICE_UUID}" = "x" ] || [ "x${GRUB_DISABLE_LINUX_UUID}" = "xtrue" ] \
     || ! test -e "/dev/disk/by-uuid/${GRUB_DEVICE_UUID}" \
     || uses_abstraction "${GRUB_DEVICE}" lvm; then
   LINUX_ROOT_DEVICE=${GRUB_DEVICE}
 else
   LINUX_ROOT_DEVICE=UUID=${GRUB_DEVICE_UUID}
 fi
 
 # Allow overriding GRUB_CMDLINE_LINUX and GRUB_CMDLINE_LINUX_DEFAULT.
 if [ "${GRUB_CMDLINE_LINUX_XEN_REPLACE}" ]; then
   GRUB_CMDLINE_LINUX="${GRUB_CMDLINE_LINUX_XEN_REPLACE}"
 fi
 if [ "${GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT}" ]; then
   GRUB_CMDLINE_LINUX_DEFAULT="${GRUB_CMDLINE_LINUX_XEN_REPLACE_DEFAULT}"
 fi
 
 if [ "x`${grub_probe} --device ${GRUB_DEVICE} --target=fs 2>/dev/null || true`" = xbtrfs ] \
     || [ "x`stat -f --printf=%T /`" = xbtrfs ]; then
   rootsubvol="`make_system_path_relative_to_its_root /`"
   rootsubvol="${rootsubvol#/}"
   if [ "x${rootsubvol}" != x ]; then
     GRUB_CMDLINE_LINUX="rootflags=subvol=${rootsubvol} ${GRUB_CMDLINE_LINUX}"
   fi
 fi
 
 linux_entry ()
 {
   os="$1"
   version="$2"
   xen_version="$3"
   recovery="$4"
   args="$5"
   xen_args="$6"
   if ${recovery} ; then
     title="$(gettext_quoted "%s, with Xen %s and Linux %s (recovery mode)")"
   else
     title="$(gettext_quoted "%s, with Xen %s and Linux %s")"
   fi
# дополнительные опции - можно выставить самому...
   printf 'set default="0" \n'
   printf 'set timeout=5 \n'
# ------------------------------------------------
   printf "menuentry '${title}' ${CLASS} {\n" "${os}" "${xen_version}" "${version}"
   if ! ${recovery} ; then
       save_default_entry | sed -e "s/^/\t/"
   fi
 
   if [ -z "${prepare_boot_cache}" ]; then
     prepare_boot_cache="$(prepare_grub_to_access_device ${GRUB_DEVICE_BOOT} | sed -e "s/^/\t/")"
   fi
   printf '%s\n' "${prepare_boot_cache}"
   xmessage="$(gettext_printf "Loading Xen %s ..." ${xen_version})"
   lmessage="$(gettext_printf "Loading Linux %s ..." ${version})"
   cat << EOF
         echo    '$xmessage'
         multiboot       ${rel_xen_dirname}/${xen_basename} placeholder ${xen_args}
         echo    '$lmessage'
         module  ${rel_dirname}/${basename} placeholder root=${linux_root_device_thisversion} ro ${args}
 EOF
   if test -n "${initrd}" ; then
     message="$(gettext_printf "Loading initial ramdisk ...")"
     cat << EOF
         echo    '$message'
         module  ${rel_dirname}/${initrd}
 EOF
   fi
   cat << EOF
 }
 EOF
 }
 
 linux_list=`for i in /boot/vmlinu[xz]-* /vmlinu[xz]-* /boot/kernel-*; do
     if grub_file_is_not_garbage "$i"; then
         basename=$(basename $i)
         version=$(echo $basename | sed -e "s,^[^0-9]*-,,g")
         dirname=$(dirname $i)
         config=
         for j in "${dirname}/config-${version}" "${dirname}/config-${alt_version}" "/etc/kernels/kernel-config-${version}" ; do
             if test -e "${j}" ; then
                 config="${j}"
                 break
             fi
         done
         if (grep -qx "CONFIG_XEN_DOM0=y" "${config}" 2> /dev/null || grep -qx "CONFIG_XEN_PRIVILEGED_GUEST=y" "${config}" 2> /dev/null); then echo -n "$i " ; fi
     fi
     done`
 if [ "x${linux_list}" = "x" ] ; then
     exit 0
 fi
 xen_list=`for i in /boot/xen*; do
         if grub_file_is_not_garbage "$i" ; then echo -n "$i " ; fi
       done`
 prepare_boot_cache=
 
 while [ "x${xen_list}" != "x" ] ; do
     list="${linux_list}"
     current_xen=`version_find_latest $xen_list`
     xen_basename=`basename ${current_xen}`
     xen_dirname=`dirname ${current_xen}`
     rel_xen_dirname=`make_system_path_relative_to_its_root $xen_dirname`
     xen_version=`echo $xen_basename | sed -e "s,.gz$,,g;s,^xen-,,g"`
     echo "submenu \"Xen ${xen_version}\" {"
     while [ "x$list" != "x" ] ; do
         linux=`version_find_latest $list`
         echo "Found linux image: $linux" >&2
         basename=`basename $linux`
         dirname=`dirname $linux`
         rel_dirname=`make_system_path_relative_to_its_root $dirname`
         version=`echo $basename | sed -e "s,^[^0-9]*-,,g"`
         alt_version=`echo $version | sed -e "s,\.old$,,g"`
         linux_root_device_thisversion="${LINUX_ROOT_DEVICE}"
 
         initrd=
         for i in "initrd.img-${version}" "initrd-${version}.img" \
             "initrd-${version}" "initrd.img-${alt_version}" \
             "initrd-${alt_version}.img" "initrd-${alt_version}" \
             "initramfs-genkernel-${version}" \
             "initramfs-genkernel-${alt_version}" ; do
             if test -e "${dirname}/${i}" ; then
                 initrd="$i"
                 break
             fi
         done
         if test -n "${initrd}" ; then
             echo "Found initrd image: ${dirname}/${initrd}" >&2
         else
     # "UUID=" magic is parsed by initrds.  Since there's no initrd, it can't work here.
             linux_root_device_thisversion=${GRUB_DEVICE}
         fi
 
         linux_entry "${OS}" "${version}" "${xen_version}" false \
             "${GRUB_CMDLINE_LINUX} ${GRUB_CMDLINE_LINUX_DEFAULT}" "${GRUB_CMDLINE_XEN} ${GRUB_CMDLINE_XEN_DEFAULT}"
         if [ "x${GRUB_DISABLE_RECOVERY}" != "xtrue" ]; then
             linux_entry "${OS}" "${version}" "${xen_version}" true \
                 "single ${GRUB_CMDLINE_LINUX}" "${GRUB_CMDLINE_XEN}"
         fi
 
         list=`echo $list | tr ' ' '\n' | grep -vx $linux | tr '\n' ' '`
     done
     echo "}"
     xen_list=`echo $xen_list | tr ' ' '\n' | grep -vx $current_xen | tr '\n' ' '`
 done

Монтирование образа хоста XEN

используем утилиту losetup:

проверяем наличие свободных устройств:

losetup -a

если все свободно, монтируем сначала образ:

losetup /dev/loop5 disk.img

смотрим смещение относительно начала:

fdisk -l /dev/loop5

пример вывода:

Disk /dev/loop5: 115.3 GB, 115343360000 bytes
255 heads, 63 sectors/track, 14023 cylinders, total 225280000 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0x390038ff

      Device Boot      Start         End      Blocks   Id  System
/dev/loop5p1   *          63   104872319    52436128+   7  HPFS/NTFS/exFAT

смещение для этого раздела равно 63, размер сектора 512 байт, для программного сдвига offset=63*512 (32256) создаем устройство типа /dev/sda1 только в варианте loop с которым будем работать:

losetup -o 32256 /dev/loop6 /dev/loop5

теперь у нас аналог /dev/sda1 только устройство /dev/loop6 можно например его примонтировать:

ntfs-3g /dev/loop6 /mnt

и делать там все что угодно..

Xen HVM guest qemu-dm USB

Qemu-dm used for Xen HVM (fully virtualized) guests supports USB passthru of devices from dom0 to the guest. Qemu-dm emulates USB 1.1 UHCI 2-port controller, which is pretty slow and limited in features and device support. Qemu-dm USB 1.1 passthru support is in all Xen 3.x (and newer) versions.

Qemu-dm USB 1.1 passthru doesn't require any additional backend drivers in dom0 or any additional frontend drivers in the guest!

As of Xen 4.2, HVM passthru is not available via xl, only xm. Support is slated for the 4.3 release.

Usage example in /etc/xen/<guest> cfgfile:

usb = 1
usbdevice = "host:xxxx:yyyy"

You can find out the "xxxx:yyyy" part by using "lsusb" command in dom0.

You can also plug a device into a running VM using usb-add and usb-del:

   xm usb-add domain host:xxxx:yyyy
   xm usb-del domain host:xxxx:yyyy