log: Add per target log levels

For CI in mkosi, I want to configure systemd to log at debug level
to the journal, but not to the console. While we already have max
level settings for journald's forwarding settings, not every log line
goes to the journal, specifically during early boot and when units
are connected directly to the console (think systemd-firstboot), so
let's extend the log level options we already have to allow specifying
a comma separated list of values and lets allow prefixing values with
the log target they apply to to make this possible.

src/basic/log.c

@@ -49,6 +49,12 @@ static void *log_syntax_callback_userdata = NULL;
 
 static LogTarget log_target = LOG_TARGET_CONSOLE;
 static int log_max_level = LOG_INFO;
+static int log_target_max_level[] = {
+        [LOG_TARGET_CONSOLE] = INT_MAX,
+        [LOG_TARGET_KMSG]    = INT_MAX,
+        [LOG_TARGET_SYSLOG]  = INT_MAX,
+        [LOG_TARGET_JOURNAL] = INT_MAX,
+};
 static int log_facility = LOG_DAEMON;
 static bool ratelimit_kmsg = true;
 
@@ -439,6 +445,9 @@ static int write_to_console(
         if (console_fd < 0)
                 return 0;
 
+        if (LOG_PRI(level) > log_target_max_level[LOG_TARGET_CONSOLE])
+                return 0;
+
         if (log_target == LOG_TARGET_CONSOLE_PREFIXED) {
                 xsprintf(prefix, "<%i>", level);
                 iovec[n++] = IOVEC_MAKE_STRING(prefix);
@@ -523,6 +532,9 @@ static int write_to_syslog(
         if (syslog_fd < 0)
                 return 0;
 
+        if (LOG_PRI(level) > log_target_max_level[LOG_TARGET_SYSLOG])
+                return 0;
+
         xsprintf(header_priority, "<%i>", level);
 
         t = (time_t) (now(CLOCK_REALTIME) / USEC_PER_SEC);
@@ -592,6 +604,9 @@ static int write_to_kmsg(
         if (kmsg_fd < 0)
                 return 0;
 
+        if (LOG_PRI(level) > log_target_max_level[LOG_TARGET_KMSG])
+                return 0;
+
         if (ratelimit_kmsg && !ratelimit_below(&ratelimit)) {
                 if (ratelimit_num_dropped(&ratelimit) > 1)
                         return 0;
@@ -719,6 +734,9 @@ static int write_to_journal(
         if (journal_fd < 0)
                 return 0;
 
+        if (LOG_PRI(level) > log_target_max_level[LOG_TARGET_JOURNAL])
+                return 0;
+
         iovec_len = MIN(6 + _log_context_num_fields * 2, IOVEC_MAX);
         iovec = newa(struct iovec, iovec_len);
 
@@ -1218,11 +1236,74 @@ int log_set_target_from_string(const char *e) {
 int log_set_max_level_from_string(const char *e) {
         int r;
 
-        r = log_level_from_string(e);
+        for (;;) {
+                _cleanup_free_ char *word = NULL, *prefix = NULL;
+                LogTarget target;
+                const char *colon;
+
+                r = extract_first_word(&e, &word, ",", 0);
+                if (r < 0)
+                        return r;
+                if (r == 0)
+                        break;
+
+                colon = strchr(word, ':');
+                if (!colon) {
+                        r = log_level_from_string(word);
+                        if (r < 0)
+                                return r;
+
+                        log_set_max_level(r);
+                        continue;
+                }
+
+                prefix = strndup(word, colon - word);
+                if (!prefix)
+                        return -ENOMEM;
+
+                target = log_target_from_string(prefix);
+                if (target < 0)
+                        return target;
+
+                if (target >= _LOG_TARGET_SINGLE_MAX)
+                        return -EINVAL;
+
+                r = log_level_from_string(colon + 1);
+                if (r < 0)
+                        return r;
+
+                log_target_max_level[target] = r;
+        }
+
+        return 0;
+}
+
+int log_max_levels_to_string(int level, char **ret) {
+        _cleanup_free_ char *s = NULL;
+        int r;
+
+        assert(ret);
+
+        r = log_level_to_string_alloc(level, &s);
         if (r < 0)
                 return r;
 
-        log_set_max_level(r);
+        for (LogTarget target = 0; target < _LOG_TARGET_SINGLE_MAX; target++) {
+                _cleanup_free_ char *l = NULL;
+
+                if (log_target_max_level[target] == INT_MAX)
+                        continue;
+
+                r = log_level_to_string_alloc(log_target_max_level[target], &l);
+                if (r < 0)
+                        return r;
+
+                r = strextendf_with_separator(&s, ",", "%s:%s", log_target_to_string(target), l);
+                if (r < 0)
+                        return r;
+        }
+
+        *ret = TAKE_PTR(s);
         return 0;
 }
 
@@ -1273,7 +1354,7 @@ static int parse_proc_cmdline_item(const char *key, const char *value, void *dat
                         return 0;
 
                 if (log_set_max_level_from_string(value) < 0)
-                        log_warning("Failed to parse log level '%s', ignoring.", value);
+                        log_warning("Failed to parse log level setting '%s', ignoring.", value);
 
         } else if (proc_cmdline_key_streq(key, "systemd.log_color")) {
 

src/basic/log.h

@@ -18,15 +18,16 @@ struct signalfd_siginfo;
 
 typedef enum LogTarget{
         LOG_TARGET_CONSOLE,
-        LOG_TARGET_CONSOLE_PREFIXED,
         LOG_TARGET_KMSG,
         LOG_TARGET_JOURNAL,
-        LOG_TARGET_JOURNAL_OR_KMSG,
         LOG_TARGET_SYSLOG,
+        LOG_TARGET_CONSOLE_PREFIXED,
+        LOG_TARGET_JOURNAL_OR_KMSG,
         LOG_TARGET_SYSLOG_OR_KMSG,
         LOG_TARGET_AUTO, /* console if stderr is not journal, JOURNAL_OR_KMSG otherwise */
         LOG_TARGET_NULL,
-        _LOG_TARGET_MAX,
+        _LOG_TARGET_SINGLE_MAX = LOG_TARGET_SYSLOG + 1,
+        _LOG_TARGET_MAX = LOG_TARGET_NULL + 1,
         _LOG_TARGET_INVALID = -EINVAL,
 } LogTarget;
 
@@ -59,6 +60,7 @@ void log_settle_target(void);
 void log_set_max_level(int level);
 int log_set_max_level_from_string(const char *e);
 int log_get_max_level(void) _pure_;
+int log_max_levels_to_string(int level, char **ret);
 
 void log_set_facility(int facility);