journald: add debug logs around offlining/archiving/rotating/varlink operations

It is not easy to understand what happens to a journal file
even with debug logs enabled. Add more dbg messages around operations
started by users to make it possible to follow the flow of operations.

src/shared/journal-file-util.c

@@ -12,7 +12,9 @@
 #include "fd-util.h"
 #include "journal-authenticate.h"
 #include "journal-file-util.h"
+#include "journal-internal.h"
 #include "log.h"
+#include "log-ratelimit.h"
 #include "set.h"
 #include "string-util.h"
 
@@ -318,12 +320,25 @@ int journal_file_set_offline(JournalFile *f, bool wait) {
 
         target_state = f->archive ? STATE_ARCHIVED : STATE_OFFLINE;
 
+        log_ratelimit_full(LOG_DEBUG,
+                           JOURNAL_LOG_RATELIMIT,
+                           "Journal file %s is %s transitioning to %s.",
+                           f->path,
+                           wait ? "synchronously" : "asynchronously",
+                           f->archive ? "archived" : "offline");
+
         /* An offlining journal is implicitly online and may modify f->header->state,
          * we must also join any potentially lingering offline thread when already in
          * the desired offline state.
          */
-        if (!journal_file_is_offlining(f) && f->header->state == target_state)
+        if (!journal_file_is_offlining(f) && f->header->state == target_state) {
+                log_ratelimit_full(LOG_DEBUG,
+                                   JOURNAL_LOG_RATELIMIT,
+                                   "Journal file %s is already %s, waiting for offlining thread.",
+                                   f->path,
+                                   f->archive ? "archived" : "offline");
                 return journal_file_set_offline_thread_join(f);
+        }
 
         /* Restart an in-flight offline thread and wait if needed, or join a lingering done one. */
         restarted = journal_file_set_offline_try_restart(f);
@@ -336,6 +351,12 @@ int journal_file_set_offline(JournalFile *f, bool wait) {
         if (restarted)
                 return 0;
 
+        log_ratelimit_full(LOG_DEBUG,
+                           JOURNAL_LOG_RATELIMIT,
+                           "Starting new %s offlining operation for journal file %s.",
+                           wait ? "synchronous" : "asynchronous",
+                           f->path);
+
         /* Initiate a new offline. */
         f->offline_state = OFFLINE_SYNCING;