Add SyslogIdentityTag

When logging to syslog, allow a tag to be added to the syslog identity
("Tor"), i.e. the string prepended to every log message.  The tag can be
configured by setting SyslogIdentityTag and defaults to none.  Setting
it to "foo" will cause logs to be tagged as "Tor-foo".  Closes: #17194.

src/common/log.c

@@ -1099,12 +1099,19 @@ add_file_log(const log_severity_list_t *severity, const char *filename,
  * Add a log handler to send messages to they system log facility.
  */
 int
-add_syslog_log(const log_severity_list_t *severity)
+add_syslog_log(const log_severity_list_t *severity, const char* syslog_identity_tag)
 {
   logfile_t *lf;
-  if (syslog_count++ == 0)
+  if (syslog_count++ == 0) {
     /* This is the first syslog. */
-    openlog("Tor", LOG_PID | LOG_NDELAY, LOGFACILITY);
+    static char buf[256];
+    if (syslog_identity_tag) {
+      tor_snprintf(buf, sizeof(buf), "Tor-%s", syslog_identity_tag);
+    } else {
+      tor_snprintf(buf, sizeof(buf), "Tor");
+    }
+    openlog(buf, LOG_PID | LOG_NDELAY, LOGFACILITY);
+  }
 
   lf = tor_malloc_zero(sizeof(logfile_t));
   lf->fd = -1;

src/common/torlog.h

@@ -135,7 +135,7 @@ void add_stream_log(const log_severity_list_t *severity, const char *name,
 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);
+int add_syslog_log(const log_severity_list_t *severity, const char* syslog_identity_tag);
 #endif
 int add_callback_log(const log_severity_list_t *severity, log_callback cb);
 void logs_set_domain_logging(int enabled);

src/or/config.c

@@ -312,6 +312,7 @@ static config_var_t option_vars_[] = {
   V(LogMessageDomains,           BOOL,     "0"),
   V(LogTimeGranularity,          MSEC_INTERVAL, "1 second"),
   V(TruncateLogFile,             BOOL,     "0"),
+  V(SyslogIdentityTag,           STRING,   NULL),
   V(LongLivedPorts,              CSV,
         "21,22,706,1863,5050,5190,5222,5223,6523,6667,6697,8300"),
   VAR("MapAddress",              LINELIST, AddressMap,           NULL),
@@ -4937,7 +4938,7 @@ options_init_logs(const or_options_t *old_options, or_options_t *options,
         !strcasecmp(smartlist_get(elts,0), "syslog")) {
 #ifdef HAVE_SYSLOG_H
       if (!validate_only) {
-        add_syslog_log(severity);
+        add_syslog_log(severity, options->SyslogIdentityTag);
       }
 #else
       log_warn(LD_CONFIG, "Syslog is not supported on this system. Sorry.");

src/or/or.h

@@ -3424,6 +3424,7 @@ typedef struct {
                           * each log message occurs? */
   int TruncateLogFile; /**< Boolean: Should we truncate the log file
                             before we start writing? */
+  char *SyslogIdentityTag; /**< Identity tag to add for syslog logging. */
 
   char *DebugLogFile; /**< Where to send verbose log messages. */
   char *DataDirectory; /**< OR only: where to store long-term data. */