[PATCH] Add session support.

[James Hunt]

Add session support. Note that there are no automatically runnable and
explicit tests yet. However, see TESTING.sessions.

* TESTING.sessions: ASCII (reStructuredText) document explaining
  how to run manual tests for session support (for chroots).
* dbus/Upstart.conf: Simplified to support allowing users to invoke
  all methods (since Upstart now isolates commands by user).
* init/Makefile.am: Added session.[ch] files.
* init/session.c: New file. Note that session_from_dbus() will disable
sessions
  (by returning the NULL session) if environment variable
"UPSTART_NO_SESSIONS"
  is set to any value (used by tests).
* init/session.h: New file.
* init/parse_job.h: parse_job(): Add session pointer to prototype.
* init/parse_job.c:
  - parse_job(): Add session parameter.
  - Update calls to job_class_new() to pass session pointer.
* init/job.c: job_new(): Crucial change to ensure chroot sessions have
  a unique D-Bus name (LP:#728531).
* init/job_class.c:
  - job_class_new(): Add session parameter and session support.
  - job_class_remove(): Add session parameter to prototype.
  - job_class_consider(): Only consider jobs from the appropriate session.
  - job_class_reconsider(): Only consider jobs from the appropriate session.
  - job_class_start(): Disallow out-of-session modification.
  - job_class_stop(): Disallow out-of-session modification.
  - job_class_restart(): Disallow out-of-session modification.
* init/main.c: Add "--no-sessions" command-line option to disable
  sessions and revert to traditional behaviour.
* init/job_class.h:
  - job_class_new(): Add session pointer to prototype.
  - JobClass: Add session member.
* init/job_process.c: job_process_spawn():
  - Call chroot(2) for chroot sessions.
  - Call setuid(2) for user session jobs.
* init/job.c:
  - job_emit_event(): Set session for event.
  - job_start(): Disallow out-of-session modification.
  - job_stop(): Disallow out-of-session modification.
  - job_restart(): Disallow out-of-session modification.
* init/event.h: Event: Add session member.
* init/event.c:
  - event_new(): initialize session to NULL.
  - event_pending_handle_jobs(): Add session handling.
  - event_finished(): Set session for failure event.
* init/control.c:
  - control_get_job_by_name(): Add session handling.
  - control_get_all_jobs(): Add session handling.
  - control_emit_event(): Add session handling.
* init/conf.c:
  - conf_source_new(): Initialise session to NULL.
  - conf_reload_path(): Pass session to parse_job().
  - conf_select_job(): Add session parameter.
* init/conf.h:
  - ConfSource: Add session member.
  - conf_select_job(): Add session parameter to prototype.
* All tests updated to set "UPSTART_NO_SESSIONS".

Code:

https://code.launchpad.net/~jamesodhunt/upstart/upstream-session-support

Merge Proposal:

https://code.launchpad.net/~jamesodhunt/upstart/upstream-session-support/+merge/63395


Regards,

James.