os/filestore/FileJournal: bail out if transaction is too large

if a transaction is too large to fit in the FileJournal's ring buffer,
we will wait. but if its size is larger than the max_size, it's likely
due to a bug or an invalid setting. in that case, we'd better fail
earlier.

Fixes: http://tracker.ceph.com/issues/16982
Signed-off-by: Kefu Chai <kchai@redhat.com>

src/os/filestore/FileJournal.cc

@@ -1667,6 +1667,7 @@ void FileJournal::submit_entry(uint64_t seq, bufferlist& e, uint32_t orig_len,
 	  << " len " << e.length()
 	  << " (" << oncommit << ")" << dendl;
   assert(e.length() > 0);
+  assert(e.length() < max_size);
 
   if (osd_op)
     osd_op->mark_event("commit_queued_for_journal_write");