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, 21 insertions, 0 deletions

diff --git a/src/journal/journald-context.h b/src/journal/journald-context.h
index eb1e21926a..d2a3772f08 100644
--- a/src/journal/journald-context.h
+++ b/src/journal/journald-context.h
@@ -60,6 +60,13 @@ struct ClientContext {
 
         char *label;
         size_t label_size;
+
+        int log_level_max;
+
+        struct iovec *extra_fields_iovec;
+        size_t extra_fields_n_iovec;
+        void *extra_fields_data;
+        nsec_t extra_fields_mtime;
 };
 
 int client_context_get(
@@ -90,3 +97,17 @@ void client_context_maybe_refresh(
 
 void client_context_acquire_default(Server *s);
 void client_context_flush_all(Server *s);
+
+static inline size_t client_context_extra_fields_n_iovec(const ClientContext *c) {
+        return c ? c->extra_fields_n_iovec : 0;
+}
+
+static inline bool client_context_test_priority(const ClientContext *c, int priority) {
+        if (!c)
+                return true;
+
+        if (c->log_level_max < 0)
+                return true;
+
+        return LOG_PRI(priority) <= c->log_level_max;
+}