[PATCH] libtracefs: New API to trace only specific functions by instance

[Sameeruddin shaik <sameeruddin.shaik8@gmail.com>]

This new API can be used to set the specific functions to be traced.

tracefs_function_filter

Signed-off-by: Sameeruddin shaik <sameeruddin.shaik8@gmail.com>

diff --git a/include/tracefs-local.h b/include/tracefs-local.h
index 187870e..e8ad1f9 100644
--- a/include/tracefs-local.h
+++ b/include/tracefs-local.h
@@ -20,6 +20,7 @@ void warning(const char *fmt, ...);
 int str_read_file(const char *file, char **buffer);
 char *trace_append_file(const char *dir, const char *name);
 char *trace_find_tracing_dir(void);
+int controlled_write(const char *path, const char* const *filter, bool reset);
 
 #ifndef ACCESSPERMS
 #define ACCESSPERMS (S_IRWXU|S_IRWXG|S_IRWXO) /* 0777 */
diff --git a/include/tracefs.h b/include/tracefs.h
index f3eec62..37eab87 100644
--- a/include/tracefs.h
+++ b/include/tracefs.h
@@ -50,6 +50,7 @@ int tracefs_trace_on(struct tracefs_instance *instance);
 int tracefs_trace_off(struct tracefs_instance *instance);
 int tracefs_trace_on_fd(int fd);
 int tracefs_trace_off_fd(int fd);
+int tracefs_function_filter(struct tracefs_instance *instance, const char* const *filter, bool reset);
 
 /**
  * tracefs_trace_on_get_fd - Get a file descriptor of "tracing_on" in given instance
diff --git a/src/tracefs-tools.c b/src/tracefs-tools.c
index e2dfc7b..709f1e7 100644
--- a/src/tracefs-tools.c
+++ b/src/tracefs-tools.c
@@ -18,6 +18,7 @@
 #include "tracefs-local.h"
 
 #define TRACE_CTRL	"tracing_on"
+#define TRACE_FILTER      "set_ftrace_filter"
 
 static const char * const options_map[] = {
 	"unknown",
@@ -387,3 +388,28 @@ void tracefs_option_clear(struct tracefs_options_mask *options, enum tracefs_opt
 	if (options && id > TRACEFS_OPTION_INVALID)
 		options->mask &= ~(1ULL << (id - 1));
 }
+
+/**
+ * tracefs_function_filter - write to set_ftrace_filter file to trace particular functions
+ * @instance: ftrace instance, can be NULL for top tracing instnace
+ * @filter: const pointer to an array of const function names
+ * @reset: Boolean value to reset the file
+ */
+int tracefs_function_filter(struct tracefs_instance *instance, const char * const *filters, bool reset)
+{
+	char *ftrace_filter_path;
+	int ret;
+
+	if (!filters)
+		return -1;
+	ftrace_filter_path = tracefs_instance_get_file(instance, TRACE_FILTER);
+
+	if (!ftrace_filter_path)
+		goto gracefully_free;
+
+	ret = controlled_write(ftrace_filter_path, filters, reset);
+
+ gracefully_free:
+	tracefs_put_tracing_file(ftrace_filter_path);
+	return ret;
+}
diff --git a/src/tracefs-utils.c b/src/tracefs-utils.c
index 0e96f8e..1cd98a2 100644
--- a/src/tracefs-utils.c
+++ b/src/tracefs-utils.c
@@ -228,3 +228,23 @@ __hidden int str_read_file(const char *file, char **buffer)
 
 	return size;
 }
+
+__hidden int controlled_write(const char *filter_path, const char * const *filters, bool reset)
+{
+	int size = 0;
+	int fd;
+	int i;
+
+	if (!filters)
+		return -1;
+	if (reset)
+		fd = open(filter_path, O_WRONLY | O_APPEND | O_TRUNC);
+	else
+		fd = open(filter_path, O_WRONLY | O_APPEND);
+	if (fd < 0)
+		return -1;
+	for (i = 0; filters[i] != NULL ; i++)
+		size += write(fd, *(filters + i), strlen(*(filters + i)));
+	close(fd);
+	return size;
+}
-- 
2.7.4