systemd: improve systemd-activate.rb script

- Pass arguments verbatim to the `systemctl` subprocess, obviating the
  need for shell escaping.

- Use open3 for capturing subprocess output.

- Fix printing of commands during dry run.

- Simplify `X-RestartIfChanged` regular expression.

  1. Use \s to match whitespace, \b to match a word boundary.

  2. Rename variable to conform to Ruby's underscore naming
     conventions.

- Remove no-op set operation. Specifically, 'no_restart' and 'to_stop'
  are disjunct since

  1. After reloading the daemon with the new generation, units in
     'to_stop' (i.e. units from the old gen that are missing in the
     new gen) are not registered anymore in the systemd daemon.

  2. Hence, 'systemctl cat' returns no output for these units.

  3. Because this output is needed to detect 'no_restart' units,
     'no_restart' includes no units from 'to_stop'.

  So 'to_stop -= to_restart' is a no-op.

- Only notify about units that would otherwise be restarted. That is,
  exclude units that are started but not restarted.

- Previously, all inactive units, like short-running services, were
  handled as failed units.

  Now systemd activation doesn't fail for oneshot services like
  'setxkbmap' while 'servicesStartTimeoutMs' is set.

- Don't start unchanged oneshot services.

PR #1110

modules/systemd-activate.rb

@@ -1,6 +1,5 @@
 require 'set'
 require 'open3'
-require 'shellwords'
 
 @dry_run = ENV['DRY_RUN']
 @verbose = ENV['VERBOSE']
@@ -28,33 +27,36 @@ def setup_services(old_gen_path, new_gen_path, start_timeout_ms_string)
 
   exit if old_services.empty? && new_services.empty?
 
+  all_services = get_active_targets_units(new_units_path)
+  maybe_changed = all_services & old_services
+  changed_services = get_changed_services(old_units_path, new_units_path, maybe_changed)
+  unchanged_oneshots = get_oneshot_services(maybe_changed - changed_services)
+
   # These services should be running when this script is finished
-  services_to_run = get_services_to_run(new_units_path)
-  maybe_changed_services = services_to_run & old_services
+  services_to_run = all_services - unchanged_oneshots
 
   # Only stop active services, otherwise we might get a 'service not loaded' error
   # for inactive services that were removed in the current generation.
   to_stop = get_active_units(old_services - new_services)
-  to_restart = get_changed_services(old_units_path, new_units_path, maybe_changed_services)
+  to_restart = changed_services
   to_start = get_inactive_units(services_to_run - to_restart)
 
-  raise "daemon-reload failed" unless run_cmd('systemctl --user daemon-reload')
+  raise "daemon-reload failed" unless run_cmd('systemctl', '--user', 'daemon-reload')
 
-  # Exclude services that aren't allowed to be manually started or stopped
+  # Exclude units that shouldn't be (re)started or stopped
   no_manual_start, no_manual_stop, no_restart = get_restricted_units(to_stop + to_restart + to_start)
-  to_stop -= no_manual_stop + no_restart
+  notify_skipped_units(to_restart & no_restart)
+  to_stop -= no_manual_stop
   to_restart -= no_manual_stop + no_manual_start + no_restart
   to_start -= no_manual_start
 
-  puts "Not restarting: #{no_restart.join(' ')}" unless no_restart.empty?
-
   if to_stop.empty? && to_start.empty? && to_restart.empty?
     print_service_msg("All services are already running", services_to_run)
   else
     puts "Setting up services" if @verbose
-    systemctl('stop', to_stop)
-    systemctl('start', to_start)
-    systemctl('restart', to_restart)
+    systemctl_action('stop', to_stop)
+    systemctl_action('start', to_start)
+    systemctl_action('restart', to_restart)
     started_services = to_start + to_restart
     if start_timeout_ms > 0 && !started_services.empty? && !@dry_run
       failed = wait_and_get_failed_services(started_services, start_timeout_ms)
@@ -89,24 +91,24 @@ end
 
 TargetDirRegexp = /^(.*\.target)\.wants$/
 
-# @return all services wanted by active targets
-def get_services_to_run(units_dir)
+# @return all units wanted by active targets
+def get_active_targets_units(units_dir)
   return Set.new unless Dir.exists?(units_dir)
   targets = Dir.entries(units_dir).map { |entry| entry[TargetDirRegexp, 1] }.compact
   active_targets = get_active_units(targets)
-  services_to_run = active_targets.map do |target|
+  active_units = active_targets.map do |target|
     get_service_files(File.join(units_dir, "#{target}.wants"))
   end.flatten
-  Set.new(services_to_run)
+  Set.new(active_units)
 end
 
 # @return true on success
-def run_cmd(cmd)
+def run_cmd(*cmd)
   print_cmd cmd
-  @dry_run || system(cmd)
+  @dry_run || system(*cmd)
 end
 
-def systemctl(cmd, services)
+def systemctl_action(cmd, services)
   return if services.empty?
 
   verb = (cmd == 'stop') ? 'Stopping' : "#{cmd.capitalize}ing"
@@ -114,7 +116,7 @@ def systemctl(cmd, services)
 
   cmd = ['systemctl', '--user', cmd, *services]
   if @dry_run
-    puts cmd
+    puts cmd.join(' ')
     return
   end
 
@@ -131,32 +133,44 @@ def systemctl(cmd, services)
   end
 end
 
+def systemctl(*cmd)
+  output, _ = Open3.capture2('systemctl', '--user', *cmd)
+  output
+end
+
 def print_cmd(cmd)
-  puts cmd if @verbose || @dry_run
+  puts [*cmd].join(' ') if @verbose || @dry_run
 end
 
 def get_active_units(units)
-  get_units_by_activity(units, true)
+  filter_units(units) { |state| state == 'active' }
 end
 
 def get_inactive_units(units)
-  get_units_by_activity(units, false)
+  filter_units(units) { |state| state != 'active' }
 end
 
-def get_units_by_activity(units, active)
+def get_failed_units(units)
+  filter_units(units) { |state| state == 'failed' }
+end
+
+def filter_units(units)
   return [] if units.empty?
-  units = units.to_a
-  is_active = `systemctl --user is-active #{units.shelljoin}`.split
+  states = systemctl('is-active', *units).split
+  units.select.with_index { |_, i| yield states[i] }
+end
+
+def get_oneshot_services(units)
+  return [] if units.empty?
+  types = systemctl('show', '-p', 'Type', *units).split
   units.select.with_index do |_, i|
-    (is_active[i] == 'active') == active
+    types[i] == 'Type=oneshot'
   end
 end
 
 def get_restricted_units(units)
-  units = units.to_a
-  infos = `systemctl --user show -p RefuseManualStart -p RefuseManualStop #{units.shelljoin}`
+  infos = systemctl('show', '-p', 'RefuseManualStart', '-p', 'RefuseManualStop', *units)
           .split("\n\n")
-  no_restart = []
   no_manual_start = []
   no_manual_stop = []
   infos.zip(units).each do |info, unit|
@@ -164,14 +178,9 @@ def get_restricted_units(units)
     no_manual_start << unit if no_start.end_with?('yes')
     no_manual_stop << unit if no_stop.end_with?('yes')
   end
-  # Regular expression that indicates that a service should not be
-  # restarted even if a change has been detected.
-  restartRe = /^[ \t]*X-RestartIfChanged[ \t]*=[ \t]*false[ \t]*(?:#.*)?$/
-  units.each do |unit|
-    if `systemctl --user cat #{unit.shellescape}` =~ restartRe
-      no_restart << unit
-    end
-  end
+  # Get units that should not be restarted even if a change has been detected.
+  no_restart_regexp = /^\s*X-RestartIfChanged\s*=\s*false\b/
+  no_restart = units.select { |unit| systemctl('cat', unit) =~ no_restart_regexp }
   [no_manual_start, no_manual_stop, no_restart]
 end
 
@@ -180,13 +189,13 @@ def wait_and_get_failed_services(services, start_timeout_ms)
   # Force the previous message to always be visible before sleeping
   STDOUT.flush
   sleep(start_timeout_ms / 1000.0)
-  get_inactive_units(services)
+  get_failed_units(services)
 end
 
 def show_failed_services_status(services)
   puts
   services.each do |service|
-    run_cmd("systemctl --user status #{service.shellescape}")
+    run_cmd('systemctl', '--user', 'status', service)
     puts
   end
 end
@@ -200,4 +209,8 @@ def print_service_msg(msg, services)
   end
 end
 
+def notify_skipped_units(no_restart)
+  puts "Not restarting: #{no_restart.join(' ')}" unless no_restart.empty?
+end
+
 setup_services(*ARGV)