sd-journal: introduce has_runtime_files and has_persistent_files

Also introduce sd_journal_has_runtime_files() and
sd_journal_has_persistent_files() to the public API. These functions
can be used to easily find out if the open journal files are runtime
and/or persistent.

src/journal/journal-internal.h

@@ -115,6 +115,8 @@ struct sd_journal {
                                   removed, and there were no more
                                   files, so sd_j_enumerate_unique
                                   will return a value equal to 0. */
+        bool has_runtime_files:1;
+        bool has_persistent_files:1;
 
         size_t data_threshold;
 

src/journal/sd-journal.c

@@ -1292,6 +1292,12 @@ static int add_file(sd_journal *j, const char *prefix, const char *filename) {
                 return 0;
 
         path = strjoina(prefix, "/", filename);
+
+        if (!j->has_runtime_files && path_startswith(path, "/run/log/journal"))
+                j->has_runtime_files = true;
+        else if (!j->has_persistent_files && path_startswith(path, "/var/log/journal"))
+                j->has_persistent_files = true;
+
         return add_any_file(j, path);
 }
 
@@ -2630,3 +2636,15 @@ _public_ int sd_journal_get_data_threshold(sd_journal *j, size_t *sz) {
         *sz = j->data_threshold;
         return 0;
 }
+
+_public_ int sd_journal_has_runtime_files(sd_journal *j) {
+        assert_return(j, -EINVAL);
+
+        return j->has_runtime_files;
+}
+
+_public_ int sd_journal_has_persistent_files(sd_journal *j) {
+        assert_return(j, -EINVAL);
+
+        return j->has_persistent_files;
+}

src/systemd/sd-journal.h

@@ -139,6 +139,9 @@ int sd_journal_reliable_fd(sd_journal *j);
 int sd_journal_get_catalog(sd_journal *j, char **text);
 int sd_journal_get_catalog_for_message_id(sd_id128_t id, char **text);
 
+int sd_journal_has_runtime_files(sd_journal *j);
+int sd_journal_has_persistent_files(sd_journal *j);
+
 /* the inverse condition avoids ambiguity of danling 'else' after the macro */
 #define SD_JOURNAL_FOREACH(j)                                           \
         if (sd_journal_seek_head(j) < 0) { }                            \