docker: improve management of avahi (#940)

Co-authored-by: Dignabbit <test@example.com>

install/docker/docker-compose.yml

@@ -37,6 +37,11 @@ services:
             # Uncomment next 3 lines for Nvidia GPU support.
             # - NVIDIA_VISIBLE_DEVICES=all
             # - NVIDIA_DRIVER_CAPABILITIES=all
+
+            # Uncomment next line to run avahi-daemon inside the container
+            # Don't use if dbus and avahi run on the host and are bind-mounted
+            # (see below under "volumes")
+            # - SCRYPTED_DOCKER_AVAHI=true
         # runtime: nvidia
 
         volumes:
@@ -56,6 +61,7 @@ services:
 
             # uncomment the following lines to expose Avahi, an mDNS advertiser.
             # make sure Avahi is running on the host machine, otherwise this will not work.
+            # not compatible with Avahi enabled via SCRYPTED_DOCKER_AVAHI=true
             # - /var/run/dbus:/var/run/dbus
             # - /var/run/avahi-daemon/socket:/var/run/avahi-daemon/socket
 

install/docker/fs/etc/s6-overlay/s6-rc.d/avahi/run

@@ -1,7 +1,7 @@
 #!/bin/bash
 
-if [ -z "$SCRYPTED_DOCKER_AVAHI" ]
-then
+if [[ "${SCRYPTED_DOCKER_AVAHI}" != "true" ]]; then
+  echo "SCRYPTED_DOCKER_AVAHI != true, not starting avahi-daemon" >/dev/stderr
   while true
   do
     sleep 1000
@@ -13,4 +13,4 @@ until [ -e /var/run/dbus/system_bus_socket ]; do
   sleep 1s
 done
 echo "Starting Avahi daemon..."
-exec avahi-daemon --no-chroot -f /etc/avahi/avahi-daemon.conf
+exec avahi-daemon --no-chroot -f /etc/avahi/avahi-daemon.conf

install/docker/fs/etc/s6-overlay/s6-rc.d/dbus/run

@@ -1,4 +1,12 @@
 #!/bin/bash
 
+if [[ "${SCRYPTED_DOCKER_AVAHI}" != "true" ]]; then
+  echo "SCRYPTED_DOCKER_AVAHI != true, not starting dbus-daemon" >/dev/stderr
+  while true
+  do
+    sleep 1000
+  done
+fi
+
 echo "Starting dbus..."
-exec dbus-daemon --system --nofork
+exec dbus-daemon --system --nofork

install/docker/fs/etc/s6-overlay/scripts/setup.sh

@@ -1,5 +1,15 @@
 #!/bin/bash
 
+if [[ "${SCRYPTED_DOCKER_AVAHI}" != "true" ]]; then
+  echo "SCRYPTED_DOCKER_AVAHI != true, won't manage dbus nor avahi-daemon" >/dev/stderr
+  exit 0
+fi
+
+if grep -qE " ((/var)?/run/dbus|(/var)?/run/avahi-daemon(/socket)?) " /proc/mounts; then
+  echo "dbus and/or avahi-daemon volumes are bind mounted, won't touch them" >/dev/stderr
+  exit 0
+fi
+
 # make run folders
 mkdir -p /var/run/dbus
 mkdir -p /var/run/avahi-daemon
@@ -22,4 +32,4 @@ if [ ! -z "$DSM_HOSTNAME" ]; then
   sed -i "s/.*host-name.*/host-name=${DSM_HOSTNAME}/" /etc/avahi/avahi-daemon.conf
 else
   sed -i "s/.*host-name.*/#host-name=/" /etc/avahi/avahi-daemon.conf
-fi
+fi