journal: normalize priority of logging sources

The stream event source has a priority of SD_EVENT_PRIORITY_NORMAL+5,
and stdout source +10, but the native and syslog event sources are left
at the default of 0.

As a result, any heavy native or syslog logger can cause starvation of
the other loggers.  This is trivially demonstrated by running:

 dd if=/dev/urandom bs=8k | od | systemd-cat & # native spammer
 systemd-run echo hello & # stream logger
 journalctl --follow --output=verbose --no-pager --identifier=echo &

... and wait, and wait, the "hello" never comes.

Now kill %1, "hello" arrives finally.

1 files changed, 4 insertions, 0 deletions

diff --git a/src/journal/journald-native.c b/src/journal/journald-native.c
index 371df5b37f..f80a6ebfe5 100644
--- a/src/journal/journald-native.c
+++ b/src/journal/journald-native.c
@@ -495,5 +495,9 @@ int server_open_native_socket(Server*s) {
         if (r < 0)
                 return log_error_errno(r, "Failed to add native server fd to event loop: %m");
 
+        r = sd_event_source_set_priority(s->native_event_source, SD_EVENT_PRIORITY_NORMAL+5);
+        if (r < 0)
+                return log_error_errno(r, "Failed to adjust native event source priority: %m");
+
         return 0;
 }