Add an option to overwrite logs

* Issue #5583

src/common/log.c

@@ -1010,12 +1010,16 @@ mark_logs_temp(void)
  * logfile fails, -1 is returned and errno is set appropriately (by open(2)).
  */
 int
-add_file_log(const log_severity_list_t *severity, const char *filename)
+add_file_log(const log_severity_list_t *severity, const char *filename,
+             const int truncate)
 {
   int fd;
   logfile_t *lf;
 
-  fd = tor_open_cloexec(filename, O_WRONLY|O_CREAT|O_APPEND, 0644);
+  int open_flags = O_WRONLY|O_CREAT;
+  open_flags |= truncate ? O_TRUNC : O_APPEND;
+
+  fd = tor_open_cloexec(filename, open_flags, 0644);
   if (fd<0)
     return -1;
   if (tor_fd_seekend(fd)<0) {
@@ -1297,3 +1301,10 @@ switch_logs_debug(void)
   UNLOCK_LOGS();
 }
 
+/** Truncate all the log files. */
+void
+truncate_logs(void)
+{
+  for (logfile_t *lf = logfiles; lf; lf = lf->next)
+    ftruncate(lf->fd, 0);
+}

src/common/torlog.h

@@ -130,7 +130,8 @@ void set_log_severity_config(int minSeverity, int maxSeverity,
                              log_severity_list_t *severity_out);
 void add_stream_log(const log_severity_list_t *severity, const char *name,
                     int fd);
-int add_file_log(const log_severity_list_t *severity, const char *filename);
+int add_file_log(const log_severity_list_t *severity, const char *filename,
+                 const int truncate);
 #ifdef HAVE_SYSLOG_H
 int add_syslog_log(const log_severity_list_t *severity);
 #endif
@@ -148,6 +149,7 @@ void change_callback_log_severity(int loglevelMin, int loglevelMax,
 void flush_pending_log_callbacks(void);
 void log_set_application_name(const char *name);
 void set_log_time_granularity(int granularity_msec);
+void truncate_logs(void);
 
 void tor_log(int severity, log_domain_mask_t domain, const char *format, ...)
   CHECK_PRINTF(3,4);