Allow to start the OSD just to flush the journal completely

src/blockstore_flush.cpp

@@ -17,8 +17,8 @@ journal_flusher_t::journal_flusher_t(blockstore_impl_t *bs)
     // FIXME: allow to configure flusher_start_threshold and journal_trim_interval
     flusher_start_threshold = bs->journal_block_size / sizeof(journal_entry_stable);
     journal_trim_interval = 512;
-    journal_trim_counter = 0;
-    trim_wanted = 0;
+    journal_trim_counter = bs->journal.flush_journal ? 1 : 0;
+    trim_wanted = bs->journal.flush_journal ? 1 : 0;
     journal_superblock = bs->journal.inmemory ? bs->journal.buffer : memalign_or_die(MEM_ALIGNMENT, bs->journal_block_size);
     co = new journal_flusher_co[max_flusher_count];
     for (int i = 0; i < max_flusher_count; i++)
@@ -626,6 +626,12 @@ resume_1:
 #endif
                 flusher->trimming = false;
             }
+            if (bs->journal.flush_journal && !flusher->flush_queue.size())
+            {
+                assert(bs->journal.used_start == bs->journal.next_free);
+                printf("Journal flushed\n");
+                exit(0);
+            }
         }
         // All done
         flusher->active_flushers--;

src/blockstore_impl.cpp

@@ -92,10 +92,23 @@ void blockstore_impl_t::loop()
             {
                 delete journal_init_reader;
                 journal_init_reader = NULL;
-                initialized = 10;
+                if (journal.flush_journal)
+                    initialized = 3;
+                else
+                    initialized = 10;
                 ringloop->wakeup();
             }
         }
+        if (initialized == 3)
+        {
+            if (readonly)
+            {
+                printf("Can't flush the journal in readonly mode\n");
+                exit(1);
+            }
+            flusher->loop();
+            ringloop->submit();
+        }
     }
     else
     {

src/blockstore_journal.h

@@ -143,6 +143,7 @@ struct journal_t
     int fd;
     uint64_t device_size;
     bool inmemory = false;
+    bool flush_journal = false;
     void *buffer = NULL;
 
     uint64_t block_size;

src/blockstore_open.cpp

@@ -42,6 +42,11 @@ void blockstore_impl_t::parse_config(blockstore_config_t & config)
     {
         disable_flock = true;
     }
+    if (config["flush_journal"] == "true" || config["flush_journal"] == "1" || config["flush_journal"] == "yes")
+    {
+        // Only flush journal and exit
+        journal.flush_journal = true;
+    }
     if (config["immediate_commit"] == "all")
     {
         immediate_commit = IMMEDIATE_ALL;
@@ -87,7 +92,7 @@ void blockstore_impl_t::parse_config(blockstore_config_t & config)
     {
         max_flusher_count = 256;
     }
-    if (!min_flusher_count)
+    if (!min_flusher_count || journal.flush_journal)
     {
         min_flusher_count = 1;
     }