core: implement /run/systemd/units/-based path for passing unit info from PID 1 to journald

And let's make use of it to implement two new unit settings with it:

1. LogLevelMax= is a new per-unit setting that may be used to configure
   log priority filtering: set it to LogLevelMax=notice and only
   messages of level "notice" and lower (i.e. more important) will be
   processed, all others are dropped.

2. LogExtraFields= is a new per-unit setting for configuring per-unit
   journal fields, that are implicitly included in every log record
   generated by the unit's processes. It takes field/value pairs in the
   form of FOO=BAR.

Also, related to this, one exisiting unit setting is ported to this new
facility:

3. The invocation ID is now pulled from /run/systemd/units/ instead of
   cgroupfs xattrs. This substantially relaxes requirements of systemd
   on the kernel version and the privileges it runs with (specifically,
   cgroupfs xattrs are not available in containers, since they are
   stored in kernel memory, and hence are unsafe to permit to lesser
   privileged code).

/run/systemd/units/ is a new directory, which contains a number of files
and symlinks encoding the above information. PID 1 creates and manages
these files, and journald reads them from there.

Note that this is supposed to be a direct path between PID 1 and the
journal only, due to the special runtime environment the journal runs
in. Normally, today we shouldn't introduce new interfaces that (mis-)use
a file system as IPC framework, and instead just an IPC system, but this
is very hard to do between the journal and PID 1, as long as the IPC
system is a subject PID 1 manages, and itself a client to the journal.

This patch cleans up a couple of types used in journal code:
specifically we switch to size_t for a couple of memory-sizing values,
as size_t is the right choice for everything that is memory.

Fixes: #4089
Fixes: #3041
Fixes: #4441

1 files changed, 7 insertions, 0 deletions

diff --git a/src/core/execute.h b/src/core/execute.h
index 23abdd4516..ab9d0dbe2d 100644
--- a/src/core/execute.h
+++ b/src/core/execute.h
@@ -212,6 +212,11 @@ struct ExecContext {
         char *syslog_identifier;
         bool syslog_level_prefix;
 
+        int log_level_max;
+
+        struct iovec* log_extra_fields;
+        size_t n_log_extra_fields;
+
         bool cpu_sched_reset_on_fork;
         bool non_blocking;
         bool private_tmp;
@@ -353,6 +358,8 @@ bool exec_context_maintains_privileges(ExecContext *c);
 
 int exec_context_get_effective_ioprio(ExecContext *c);
 
+void exec_context_free_log_extra_fields(ExecContext *c);
+
 void exec_status_start(ExecStatus *s, pid_t pid);
 void exec_status_exit(ExecStatus *s, ExecContext *context, pid_t pid, int code, int status);
 void exec_status_dump(ExecStatus *s, FILE *f, const char *prefix);