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, 22 insertions, 11 deletions

diff --git a/src/journal/journald-server.c b/src/journal/journald-server.c
index e85e4e0f10..033f0b1a8b 100644
--- a/src/journal/journald-server.c
+++ b/src/journal/journald-server.c
@@ -753,7 +753,7 @@ static void write_to_journal(Server *s, uid_t uid, struct iovec *iovec, unsigned
 
 static void dispatch_message_real(
                 Server *s,
-                struct iovec *iovec, unsigned n, unsigned m,
+                struct iovec *iovec, size_t n, size_t m,
                 const ClientContext *c,
                 const struct timeval *tv,
                 int priority,
@@ -766,7 +766,10 @@ static void dispatch_message_real(
         assert(s);
         assert(iovec);
         assert(n > 0);
-        assert(n + N_IOVEC_META_FIELDS + (pid_is_valid(object_pid) ? N_IOVEC_OBJECT_FIELDS : 0) <= m);
+        assert(n +
+               N_IOVEC_META_FIELDS +
+               (pid_is_valid(object_pid) ? N_IOVEC_OBJECT_FIELDS : 0) +
+               client_context_extra_fields_n_iovec(c) <= m);
 
         if (c) {
                 IOVEC_ADD_NUMERIC_FIELD(iovec, n, c->pid, pid_t, pid_is_valid, PID_FMT, "_PID");
@@ -792,6 +795,11 @@ static void dispatch_message_real(
                 IOVEC_ADD_STRING_FIELD(iovec, n, c->user_slice, "_SYSTEMD_USER_SLICE");
 
                 IOVEC_ADD_ID128_FIELD(iovec, n, c->invocation_id, "_SYSTEMD_INVOCATION_ID");
+
+                if (c->extra_fields_n_iovec > 0) {
+                        memcpy(iovec + n, c->extra_fields_iovec, c->extra_fields_n_iovec * sizeof(struct iovec));
+                        n += c->extra_fields_n_iovec;
+                }
         }
 
         assert(n <= m);
@@ -862,14 +870,17 @@ static void dispatch_message_real(
 
 void server_driver_message(Server *s, pid_t object_pid, const char *message_id, const char *format, ...) {
 
-        struct iovec iovec[N_IOVEC_META_FIELDS + 5 + N_IOVEC_PAYLOAD_FIELDS];
-        unsigned n = 0, m;
+        struct iovec *iovec;
+        size_t n = 0, k, m;
         va_list ap;
         int r;
 
         assert(s);
         assert(format);
 
+        m = N_IOVEC_META_FIELDS + 5 + N_IOVEC_PAYLOAD_FIELDS + client_context_extra_fields_n_iovec(s->my_context);
+        iovec = newa(struct iovec, m);
+
         assert_cc(3 == LOG_FAC(LOG_DAEMON));
         iovec[n++] = IOVEC_MAKE_STRING("SYSLOG_FACILITY=3");
         iovec[n++] = IOVEC_MAKE_STRING("SYSLOG_IDENTIFIER=systemd-journald");
@@ -880,18 +891,18 @@ void server_driver_message(Server *s, pid_t object_pid, const char *message_id,
 
         if (message_id)
                 iovec[n++] = IOVEC_MAKE_STRING(message_id);
-        m = n;
+        k = n;
 
         va_start(ap, format);
-        r = log_format_iovec(iovec, ELEMENTSOF(iovec), &n, false, 0, format, ap);
+        r = log_format_iovec(iovec, m, &n, false, 0, format, ap);
         /* Error handling below */
         va_end(ap);
 
         if (r >= 0)
-                dispatch_message_real(s, iovec, n, ELEMENTSOF(iovec), s->my_context, NULL, LOG_INFO, object_pid);
+                dispatch_message_real(s, iovec, n, m, s->my_context, NULL, LOG_INFO, object_pid);
 
-        while (m < n)
-                free(iovec[m++].iov_base);
+        while (k < n)
+                free(iovec[k++].iov_base);
 
         if (r < 0) {
                 /* We failed to format the message. Emit a warning instead. */
@@ -902,13 +913,13 @@ void server_driver_message(Server *s, pid_t object_pid, const char *message_id,
                 n = 3;
                 iovec[n++] = IOVEC_MAKE_STRING("PRIORITY=4");
                 iovec[n++] = IOVEC_MAKE_STRING(buf);
-                dispatch_message_real(s, iovec, n, ELEMENTSOF(iovec), s->my_context, NULL, LOG_INFO, object_pid);
+                dispatch_message_real(s, iovec, n, m, s->my_context, NULL, LOG_INFO, object_pid);
         }
 }
 
 void server_dispatch_message(
                 Server *s,
-                struct iovec *iovec, unsigned n, unsigned m,
+                struct iovec *iovec, size_t n, size_t m,
                 ClientContext *c,
                 const struct timeval *tv,
                 int priority,