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

[Scott Moser]

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>

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" "$@"
     else
         _LXC_HOOK=""
         prep "$@"