Truncate log and hpfs index file from given sequence number. (#276)

- Truncation is invoked by making truncate system call on /hpfs::index.<seq_no> file.
- Updating hpfs binary.
- Truncation waits until any active RW and RO sessions are finished.

src/hpfs/hpfs_mount.cpp

@@ -412,4 +412,22 @@ namespace hpfs
         return 0;
     }
 
+    /**
+     * Invoke log file and hpfs index file starting from the given sequence number. This function is a blocking call.
+     * @param seq_no Sequence number to start truncation from.
+     * @return Returns -1 on error and 0 on success.
+    */
+    int hpfs_mount::truncate_log_file(const uint64_t seq_no)
+    {
+        const std::string file_path = mount_dir + INDEX_UPDATE + "." + std::to_string(seq_no);
+        // File /hpfs::index.<seq_no> is truncated to invoke log file truncation in hpfs.
+        // This call waits until any running RW or RO sessions stop.
+        if (truncate(file_path.c_str(), 0) == -1)
+        {
+            LOG_ERROR << errno << ": Error truncating log file for seq_no: " << std::to_string(seq_no);
+            return -1;
+        }
+        return 0;
+    }
+
 } // namespace hpfs

src/hpfs/hpfs_mount.hpp

@@ -68,6 +68,7 @@ namespace hpfs
         const util::h32 get_parent_hash(const std::string &parent_vpath);
         void set_parent_hash(const std::string &parent_vpath, const util::h32 new_state);
         int update_hpfs_log_index();
+        int truncate_log_file(const uint64_t seq_no);
     };
 
 } // namespace hpfs