[lxc-devel] ubuntu-cloud-prep: patch /sbin/start for overlayfs

[Serge Hallyn]

Quoting Scott Moser (smoser at ubuntu.com):
> upstart depends on inotify, and overlayfs does not support inotify.
> 
> That means that the following results in 'tgt' not running. tgt is simply
> used here as an example of a service that installs an upstart job and
> starts it on package install.
>  lxc-clone -s -B overlayfs -o source-precise-amd64 -n test1
>  lxc-start -n test1
>  ..
>  apt-get install tgt
> 
> The change here is to modify /sbin/start inside the container so that when
> something explicitly tries 'start', it results in an explicit call to
> 'initctl reload-configuration' so that upstart is aware of the newly
> placed job.
> 
> Should overlayfs ever gain inotify support, this should still not cause
> any harm.
> 
> Signed-off-by: Scott Moser <smoser at ubuntu.com>

Acked-by: Serge E. Hallyn <serge.hallyn at ubuntu.com>

applied, thanks

> diff --git a/hooks/ubuntu-cloud-prep b/hooks/ubuntu-cloud-prep
> index 7985a73..5e0a999 100755
> --- a/hooks/ubuntu-cloud-prep
> +++ b/hooks/ubuntu-cloud-prep
> @@ -12,6 +12,7 @@
>  ##  LXC_SRC_NAME:     old container name
>  ##  LXC_ROOTFS_PATH:  path or device on which the root fs is located
> 
> +set -f
>  VERBOSITY="0"
> 
>  error() { echo "$@" 1>&2; }
> @@ -34,9 +35,56 @@ Usage: ${0##*/} [options] root-dir
>  EOF
>  }
> 
> +write_patched_start() {
> +    cat > "$1" <<"EOF"
> +#!/bin/bash
> +## This is a wrapper around upstart's /sbin/start to ensure that
> +## calling 'start' on a job after writing it to /etc/init will function
> +## correctly despite broken/missing support for inotify in overlayfs.
> +##
> +real() { exec -a /sbin/start "/sbin/start.real" "$@"; }
> +
> +# no args or not root
> +[ $# -ne 0 -a "$UID" = "0" ] || real "$@"
> +
> +job=""
> +# find first argument that doesn't start with '-' as 'job'
> +for x in "$@"; do
> +  [ "${x#-}" = "$x" ] && { job="$x"; break; }
> +done
> +
> +# if job isn't there, no reason to check further
> +[ -n "$job" ] && [ -f "/etc/init/$job.conf" ] || real "$@"
> +
> +# on Unknown, 'status' exits 1, and prints 'Unknown job' to stderr.
> +out=$(status "$@" 2>&1)
> +[ $? -eq 1 -a "${out#*nknown job}" != "$out" ] || real "$@"
> +
> +initctl reload-configuration >/dev/null 2>&1
> +real "$@"
> +EOF
> +    chmod 755 "$1"
> +}
> +
> +patch_start() {
> +    # patch /sbin/start inside root_d to deal with lack of inotify
> +    local root_d="$1"
> +
> +    # already patched
> +    [ -f "$root_d/sbin/start.real" ] &&
> +        { debug 1 "$root_d 'start' seems already patched"; return 1; }
> +
> +    debug 1 "patching /sbin/start in $root_d"
> +    chroot "$root_d" dpkg-divert --local --rename \
> +        --divert /sbin/start.real --add /sbin/start ||
> +        { error "failed to patch /sbin/start for overlayfs"; return 1; }
> +
> +    write_patched_start "$root_d/sbin/start"
> +}
> +
>  prep() {
>      local short_opts="Chi:L:S:u:v"
> -    local long_opts="auth-key:,cloud,help,hostid:,name:,nolocales:,userdata:,verbose"
> +    local long_opts="auth-key:,cloud,help,hostid:,name:,nolocales:,patch-start,userdata:,verbose"
>      local getopt_out getopt_ret
>      getopt_out=$(getopt --name "${0##*/}" \
>          --options "${short_opts}" --long "${long_opts}" -- "$@" 2>/dev/null) ||
> @@ -49,6 +97,8 @@ prep() {
> 
>      local cur="" next=""
>      local userdata="" hostid="" authkey="" locales=1 cloud=0 name=""
> +    local patch_start=0
> +
>      while [ $# -ne 0 ]; do
>          cur="$1"; next="$2";
>          case "$cur" in
> @@ -57,6 +107,7 @@ prep() {
>                 --name) name="$next";;
>              -i|--hostid) hostid="$next";;
>              -L|--nolocales) locales=0;;
> +               --patch-start) patch_start=1;;
>              -S|--auth-key)
>                  [ -f "$next" ] ||
>                      { error "--auth-key: '$next' not a file"; return 1; }
> @@ -86,6 +137,9 @@ prep() {
>          error "${0##*}: usage failed, continuing with defaults"
>      fi
> 
> +    [ "$patch_start" -eq 0 ] || patch_start "$root_d" ||
> +        { error "failed to patch start for overlayfs"; return 1; }
> +
>      local seed_d=""
>      seed_d="$root_d/var/lib/cloud/seed/nocloud-net"
>      if [ $cloud -eq 1 ]; then
> @@ -149,10 +203,13 @@ main() {
>      local _LXC_HOOK
>      if [ -n "$LXC_ROOTFS_MOUNT" -a "$3" = "clone" ]; then
>          _LXC_HOOK="clone"
> -        local name="$1"
> +        local name="$1" pstart=""
>          shift 3
> -        debug 1 prep "--name=$name" "$LXC_ROOTFS_MOUNT" "$@"
> -        prep "--name=$name" "$LXC_ROOTFS_MOUNT" "$@"
> +        # if mountpoint is overlayfs then add '--patch-start'
> +        [ "${LXC_ROOTFS_PATH#overlayfs}" != "${LXC_ROOTFS_PATH}" ] &&
> +           pstart="--patch-start"
> +        debug 1 prep "--name=$name" $pstart "$LXC_ROOTFS_MOUNT" "$@"
> +        prep "--name=$name" $pstart "$LXC_ROOTFS_MOUNT" "$@"
>      else
>          _LXC_HOOK=""
>          prep "$@"
> 
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