journald: use the event loop dispatch timestamp for journal entries

Let's use the earliest linearized event timestamp for journal entries we have:
the event dispatch timestamp from the event loop, instead of requerying the
timestamp at the time of writing.

This makes the time a bit more accurate, allows us to query the kernel time one
time less per event loop, and also makes sure we always use the same timestamp
for both attempts to write an entry to a journal file.

diff --git a/src/journal/journald-server.c b/src/journal/journald-server.c
index f01cf1d..7227c80 100644 (file)
--- a/src/journal/journald-server.c
+++ b/src/journal/journald-server.c
@@ -627,14 +627,21 @@ static bool shall_try_append_again(JournalFile *f, int r) {
 }
 
 static void write_to_journal(Server *s, uid_t uid, struct iovec *iovec, unsigned n, int priority) {
-        JournalFile *f;
+        struct dual_timestamp ts;
         bool vacuumed = false;
+        JournalFile *f;
         int r;
 
         assert(s);
         assert(iovec);
         assert(n > 0);
 
+        /* Get the closest, linearized time we have for this log event from the event loop. (Note that we do not use
+         * the source time, and not even the time the event was originally seen, but instead simply the time we started
+         * processing it, as we want strictly linear ordering in what we write out.) */
+        assert_se(sd_event_now(s->event, CLOCK_REALTIME, &ts.realtime) >= 0);
+        assert_se(sd_event_now(s->event, CLOCK_MONOTONIC, &ts.monotonic) >= 0);
+
         f = find_journal(s, uid);
         if (!f)
                 return;
@@ -650,7 +657,7 @@ static void write_to_journal(Server *s, uid_t uid, struct iovec *iovec, unsigned
                         return;
         }
 
-        r = journal_file_append_entry(f, NULL, iovec, n, &s->seqnum, NULL, NULL);
+        r = journal_file_append_entry(f, &ts, iovec, n, &s->seqnum, NULL, NULL);
         if (r >= 0) {
                 server_schedule_sync(s, priority);
                 return;
@@ -669,7 +676,7 @@ static void write_to_journal(Server *s, uid_t uid, struct iovec *iovec, unsigned
                 return;
 
         log_debug("Retrying write.");
-        r = journal_file_append_entry(f, NULL, iovec, n, &s->seqnum, NULL, NULL);
+        r = journal_file_append_entry(f, &ts, iovec, n, &s->seqnum, NULL, NULL);
         if (r < 0)
                 log_error_errno(r, "Failed to write entry (%d items, %zu bytes) despite vacuuming, ignoring: %m", n, IOVEC_TOTAL_SIZE(iovec, n));
         else