journal: optimize iteration by skipping exhausted files

If from a previous iteration we know we are at the end of a journal
file, don't bother looking into the file again. This is complicated by
the fact that the EOF does not have to be permanent (think of
"journalctl -f"). So we also check if the number of entries in the
journal file changed.

This optimization has a similar effect as "journal: optimize iteration:
skip whole files behind current location" had.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/journal/journal-file.h b/src/journal/journal-file.h
index 8084176195..561982fe39 100644
--- a/src/journal/journal-file.h
+++ b/src/journal/journal-file.h
@@ -78,6 +78,7 @@ typedef struct JournalFile {
 
         direction_t last_direction;
         LocationType location_type;
+        uint64_t last_n_entries;
 
         char *path;
         struct stat last_stat;