[PATCH] libtracefs: An API to set the filtering of functions

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

This new API will write the function filters into the
set_ftrace_filter file.

tracefs_function_filter()

https://bugzilla.kernel.org/show_bug.cgi?id=210643

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

diff --git a/include/tracefs.h b/include/tracefs.h
index f3eec62..a2249d0 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 **filters, const char *module, bool reset, const char ***errs);
 
 /**
  * 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..4e168df 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 +388,96 @@ void tracefs_option_clear(struct tracefs_options_mask *options, enum tracefs_opt
 	if (options && id > TRACEFS_OPTION_INVALID)
 		options->mask &= ~(1ULL << (id - 1));
 }
+
+static int controlled_write(const char *filter_path, const char **filters, const char *module, bool reset, const char ***errs)
+{
+	int flags = reset ? O_TRUNC : O_APPEND;
+	int write_size;
+	char *each_str;
+	int ret = 0;
+	int j = 0;
+	int size;
+	int slen;
+	int fd;
+	int i;
+
+	fd = open(filter_path, O_WRONLY | flags);
+	if (fd < 0)
+		return 1;
+
+	for (i = 0; filters[i]; i++) {
+		slen = strlen(filters[i]);
+		if (!slen)
+			continue;
+
+		if (module)
+			/* Adding 5 extra bytes for ":mod:"*/
+			slen += strlen(module) + 5;
+
+		/* Adding 2 extra byte for the space and '\0' at the end*/
+		slen += 2;
+		each_str = calloc(1, slen);
+		if (!each_str)
+			return 1;
+		if (module)
+			write_size = snprintf(each_str, slen, "%s:mod:%s ", filters[i], module);
+		else
+			write_size = snprintf(each_str, slen, "%s ", filters[i]);
+
+		size = write(fd, each_str, write_size);
+		/* compare written bytes*/
+		if (size < write_size) {
+			if (errs) {
+				errs[j++] = &filters[i];
+				ret -= 1;
+			}
+		}
+		free(each_str);
+	}
+	errs[j] = NULL;
+	close(fd);
+	return ret;
+}
+
+/**
+ * tracefs_function_filter - write to set_ftrace_filter file to trace particular functions
+ * @instance: ftrace instance, can be NULL for top tracing instance
+ * @filters: An array of function names ending with a NULL pointer
+ * @module: Module to be traced
+ * @reset: set to true to reset the file before applying the filter
+ * @errs: A pointer to array of constant strings that will be allocated
+ * on negative return of this function, pointing to the filters that failed.
+ * May be NULL, in which case this field will be ignored.
+ *
+ * The @filters is an array of strings, where each string will be used to set
+ * a function or functions to be traced.
+ *
+ * If @reset is true, then all functions in the filter are cleared before
+ * adding functions from @filters. Otherwise, the functions set by @filters
+ * will be appended to the filter file
+ *
+ * returns -x on filter errors (where x is number of failed filter srtings)
+ * and if @errs is not NULL will be an allocated string array pointing to the
+ * strings in @filters that failed and must be freed with free().
+ *
+ * returns 1 on general errors not realted to setting the filter.
+ * @errs is not set even if supplied.
+ *
+ * return 0 on success and @errs is not set.
+ */
+int tracefs_function_filter(struct tracefs_instance *instance, const char **filters, const char *module, bool reset, const char ***errs)
+{
+	char *ftrace_filter_path;
+	int ret = 0;
+
+	if (!filters)
+		return 1;
+
+	ftrace_filter_path = tracefs_instance_get_file(instance, TRACE_FILTER);
+	if (!ftrace_filter_path)
+		return 1;
+
+	ret = controlled_write(ftrace_filter_path, filters, module, reset, errs);
+	tracefs_put_tracing_file(ftrace_filter_path);
+	return ret;
+}
-- 
2.7.4