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Re: update-grub & Xen boot stanza generation

From: Bruce Edge
Subject: Re: update-grub & Xen boot stanza generation
Date: Mon, 24 May 2010 10:00:48 -0700


On Mon, May 24, 2010 at 9:45 AM, Isaac Dupree <address@hidden> wrote:
On 05/24/10 00:48, Joey Korkames wrote:
 This is aready worked on but the problem is that it generates too much
entries. If you have 5 different versions of hypervisor and 10
kernels you have 100 entries.

What if I add a max_entries option. Say, don't generate more than 4
stanzas total. Although I suppose then I need to go through and pick
the most recent kernel and hypervisor versions.

It feels like a kludgy solution

It seems like the non-kludgy setup (while avoiding quadratic menu sizes) would be one in which, in one menu you pick which Xen hypervisor, and in the next menu you pick which Xen kernel. Is that feasible to implement? useful?


The script below contains the fixes mentioned in the thread so far.
It only generates menu entries using the one xen.gz hypervisor to eliminate the geometric entry number problem. The most recently installed hypervisor overwrites this symlink with one pointing to itself. The result is that you will only have entries for one hypervisor * the number of dom0 capable kernels. 

I made one more change such that if GRUB_CMDLINE_XEN_DEFAULT is not in /etc/default/grub, then it will ignore xen completely and not generate any additional boot entries. This should make it undetectable by anyone not explicitly wanting Xen boot entries.

Feel free to strip the header, reformat, whatever. 


#!/bin/bash -e
#          FILE:  09_xen
#         USAGE:  update-grub ... with this in /etc/grub.d
#   DESCRIPTION: Generate grub2 boot stanza for Xen systems
#                               Xen boot entries are automatically added to grub.cfg
#                               The 09-... name prefix puts the Xen boot entries before 
#                               the linux kernel entries
#       OPTIONS:  ---
#  REQUIREMENTS:  --- grub2, Xen hypervisor
#          BUGS:  --- probably
#         NOTES:  --- Copied from 10_linux with a few hacks to make ir work for Xen.
#                                       Incorporated suggestions to only do this for valid dom0 kernels
#        AUTHOR:  Bruce Edge (BRE), address@hidden 
#       COMPANY:  LSI
#       VERSION:  1.0
#       CREATED:  05/19/2010 02:32:34 PM PDT
#      REVISION:  ---

. ${libdir}/grub/update-grub_lib

if [ "x${GRUB_DISTRIBUTOR}" = "x" ] ; then

# Source grub defaults
. /etc/default/grub

# 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
    GRUB_DEVICE=`losetup ${GRUB_DEVICE} | sed -e "s/^[^(]*(\([^)]\+\)).*/\1/"`

if [ "x${GRUB_DEVICE_UUID}" = "x" ] || [ "x${GRUB_DISABLE_LINUX_UUID}" = "xtrue" ] \
    || ! test -e "/dev/disk/by-uuid/${GRUB_DEVICE_UUID}" ; then

test_gt ()
  local a=`echo $1 | sed -e "s,.*/vmlinu[zx]-,,g;s/[._-]\(pre\|rc\|test\|git\|old\)/~\1/g"`
  local b=`echo $2 | sed -e "s,.*/vmlinu[zx]-,,g;s/[._-]\(pre\|rc\|test\|git\|old\)/~\1/g"`
  if [ "x$b" = "x" ] ; then
    return 0
  dpkg --compare-versions "$a" gt "$b"
  return $?

find_latest ()
  local a=""
  for i in $@ ; do
    if test_gt "$i" "$a" ; then
  echo "$a"

list=`for i in /boot/vmlinu[xz]-* /vmlinu[xz]-* ; do
        if grub_file_is_not_garbage "$i" && grep -q 'DOM0=y' ${i/vmlinu[xz]/config} ; then echo -n "$i " ; fi

grub -q GRUB_CMDLINE_XEN_DEFAULT || list=""

while [ "x$list" != "x" ] ; do
  linux=`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"`

  for i in "initrd.img-${version}" "initrd-${version}.img" \
           "initrd.img-${alt_version}" "initrd-${alt_version}.img"; do
    if test -e "${dirname}/${i}" ; then
  if test -n "${initrd}" ; then
    echo "Found initrd image: ${dirname}/${initrd}" >&2
    # "UUID=" magic is parsed by initrds.  Since there's no initrd, it can't work here.

  cat << EOF
  insmod lvm
  set root=(system-dom0_0)
menuentry "Xen ${OS}, linux ${version}" {
        multiboot /boot/xen.gz dummy=dummy $GRUB_CMDLINE_XEN_DEFAULT
        module ${rel_dirname}/${basename} root=${linux_root_device_thisversion} $GRUB_CMDLINE_LINUX_DEFAULT
  if test -n "${initrd}" ; then
    cat << EOF
        module ${rel_dirname}/${initrd} ${rel_dirname}/${initrd}
  cat << EOF

  list=`echo $list | tr ' ' '\n' | grep -vx $linux | tr '\n' ' '`

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