ftrace_log: Add override for tracefs location

doc/tutorial.txt

@@ -92,6 +92,10 @@ The category names currently supported are:
 
 Default value is "none".
 
+* ftracedir : String. Mountpoint of tracefs. Defaults to
+"/sys/kernel/debug/tracing" if not specified. Has no effect if ftrace is not
+enabled.
+
 * gnuplot : Boolean. If True, it will create a gnu plot compatible file for
 each threads (see gnuplot section for more details). Default value is False.
 

src/rt-app.c

@@ -64,7 +64,6 @@ static pthread_mutex_t joining_mutex;
 static pthread_mutex_t fork_mutex;
 
 static ftrace_data_t ft_data = {
-	.debugfs = "/sys/kernel/debug",
 	.marker_fd = -1,
 };
 
@@ -1542,8 +1541,8 @@ int main(int argc, char* argv[])
 	if (ftrace_level != FTRACE_NONE) {
 		log_notice("configuring ftrace");
 		// check if tracing is enabled
-		strcpy(tmp, ft_data.debugfs);
-		strcat(tmp, "/tracing/tracing_on");
+		strcpy(tmp, opts.ftracedir);
+		strcat(tmp, "/tracing_on");
 		int ftrace_f = open(tmp, O_RDONLY);
 		if (ftrace_f < 0){
 			log_error("Cannot open tracing_on file %s", tmp);
@@ -1557,8 +1556,8 @@ int main(int argc, char* argv[])
 		}
 		close(ftrace_f);
 		// set the marker
-		strcpy(tmp, ft_data.debugfs);
-		strcat(tmp, "/tracing/trace_marker");
+		strcpy(tmp, opts.ftracedir);
+		strcat(tmp, "/trace_marker");
 		ft_data.marker_fd = open(tmp, O_WRONLY);
 		if (ft_data.marker_fd < 0) {
 			log_error("Cannot open trace_marker file %s", tmp);

src/rt-app_parse_config.c

@@ -1207,6 +1207,7 @@ parse_global(struct json_object *global, rtapp_options_t *opts)
 		opts->io_device = strdup("/dev/null");
 		opts->mem_buffer_size = DEFAULT_MEM_BUF_SIZE;
 		opts->cumulative_slack = 0;
+		opts->ftracedir = ftrace_dir();
 		return;
 	}
 
@@ -1304,6 +1305,7 @@ parse_global(struct json_object *global, rtapp_options_t *opts)
 	    log_critical(PFX "Invalid ftrace categories");
 	    exit(EXIT_INV_CONFIG);
 	}
+	opts->ftracedir = get_string_value_from(global, "ftracedir", TRUE, ftrace_dir());
 
 	opts->lock_pages = get_bool_value_from(global, "lock_pages", TRUE, 1);
 	opts->pi_enabled = get_bool_value_from(global, "pi_enabled", TRUE, 0);

src/rt-app_types.h

@@ -289,6 +289,8 @@ typedef struct _rtapp_options_t {
 	char *io_device;
 
 	int cumulative_slack;
+
+	char *ftracedir; /* should end in 'tracing' */
 } rtapp_options_t;
 
 typedef struct _timing_point_t {

src/rt-app_utils.c

@@ -25,6 +25,7 @@ Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 #include <errno.h>
 #include <math.h>
 #include <stdarg.h>
+#include <mntent.h>
 
 #include "rt-app_utils.h"
 
@@ -267,6 +268,60 @@ resource_to_string(resource_t resource, char *resource_name)
 	return 0;
 }
 
+/* point directly to the tracing directory */
+#define DEFAULT_FTRACE_DIR "/sys/kernel/debug/tracing"
+
+char *mtab_by_type(const char *type, int typelen)
+{
+	FILE *fd_mntent;
+
+	fd_mntent = setmntent("/etc/mtab", "r");
+	if(fd_mntent)
+	{
+		struct mntent *mntent;
+
+		while(mntent = getmntent(fd_mntent), mntent)
+		{
+			log_debug("mntent->dir=%s type=%s", mntent->mnt_dir, mntent->mnt_type);
+			if(!strncmp(type, mntent->mnt_type, typelen))
+			{
+				char *path = strdup(mntent->mnt_dir);
+				endmntent(fd_mntent);
+				return path;
+			}
+		}
+		endmntent(fd_mntent);
+	}
+	return NULL;
+}
+
+char *ftrace_dir(void)
+{
+	char *path;
+
+	/* tracefs paths point directly to the tracing directory */
+	path = mtab_by_type("tracefs", sizeof("tracefs")-1);
+	if(path)
+		return path;
+
+	/* debugfs paths point one level above the tracing directory */
+	path = mtab_by_type("debugfs", sizeof("debugfs")-1);
+	if(path)
+	{
+		char *tmp;
+		int len = strlen(path) + sizeof("/tracing");
+		tmp = malloc(len);
+		if(!tmp)
+			return NULL;
+		strcpy(tmp, path);
+		free(path);
+		strcat(tmp, "/tracing");
+		return tmp;
+	}
+
+	return strdup(DEFAULT_FTRACE_DIR);
+}
+
 int ftrace_setup(char *categories)
 {
 	char *cat = strtok(categories, ",");

src/rt-app_utils.h

@@ -141,6 +141,10 @@ string_to_resource(const char *name, resource_t *resource);
 int
 resource_to_string(resource_t resource, char *name);
 
+/* ftrace_dir always returns a string on the heap */
+char *
+ftrace_dir(void);
+
 int
 ftrace_setup(char *categories);