Follow OpenOCD style guide.

Change-Id: I1105c9d570890423f2712919bdaba26fdd09acab

doc/openocd.texi

@@ -7702,8 +7702,9 @@ echo "Downloading kernel -- please wait"
 @end deffn
 
 @deffn Command log_output [filename]
-Redirect logging to @var{filename};
+Redirect logging to @var{filename}. If @var{filename} is >stdout or >stderr,
-the initial log output channel is stderr.
+then logging is redirected to stdout and stderr respectively.
+The initial log output channel is stderr.
 @end deffn
 
 @deffn Command add_script_search_dir [directory]

src/helper/log.c

@@ -221,12 +221,18 @@ COMMAND_HANDLER(handle_debug_level_command)
 COMMAND_HANDLER(handle_log_output_command)
 {
 	if (CMD_ARGC == 1) {
-		FILE *file = fopen(CMD_ARGV[0], "w");
+		FILE *file = NULL;
+		if (!strcmp(CMD_ARGV[0], ">stdout"))
+			file = stdout;
+		else if (!strcmp(CMD_ARGV[0], ">stderr"))
+			file = stderr;
+		else
+			file = fopen(CMD_ARGV[0], "w");
 		if (file == NULL) {
 			LOG_ERROR("failed to open output log '%s'", CMD_ARGV[0]);
 			return ERROR_FAIL;
 		}
-		if (log_output != stderr && log_output != NULL) {
+		if (log_output != stdout && log_output != stderr && log_output != NULL) {
 			/* Close previous log file, if it was open and wasn't stderr. */
 			fclose(log_output);
 		}
@@ -285,12 +291,6 @@ void log_init(void)
 	start = last_time = timeval_ms();
 }
 
-int set_log_output(struct command_context *cmd_ctx, FILE *output)
-{
-	log_output = output;
-	return ERROR_OK;
-}
-
 /* add/remove log callback handler */
 int log_add_callback(log_callback_fn fn, void *priv)
 {