1 files changed, 16 insertions, 2 deletions
diff --git a/src/common/lock.cpp b/src/common/lock.cpp
index a708c40..82856e1 100644
--- a/src/common/lock.cpp
+++ b/src/common/lock.cpp
@@ -9,6 +9,10 @@
 
 #include "../poison.hpp"
 
+/// number of backups to keep
+static
+const int backup_count = 10;
+
 /// Protected file writing
 /// (Until the file is closed, it keeps the old file)
 
@@ -36,7 +40,17 @@ void lock_fclose(FILE *fp, const char *filename, int *info)
     if (fp)
     {
         fclose_(fp);
-        std::string newfile = STRPRINTF("%s_%d.tmp", filename, *info);
-        rename(newfile.c_str(), filename);
+        int n = backup_count;
+        std::string old_filename = STRPRINTF("%s.%d", filename, n);
+        while (--n)
+        {
+            std::string newer_filename = STRPRINTF("%s.%d", filename, n);
+            rename(newer_filename.c_str(), old_filename.c_str());
+            old_filename = std::move(newer_filename);
+        }
+        rename(filename, old_filename.c_str());
+
+        std::string tmpfile = STRPRINTF("%s_%d.tmp", filename, *info);
+        rename(tmpfile.c_str(), filename);
     }
 }