[PATCH v4 1/4] trace-cmd: Add new tracefs APIs for checking if a ftrace file / directory exists

["Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com>]

Some ftrace files and directories are optional, depending on specific kernel configuration or version.
It is a good practice to check if the file / directory exist, before trying to access it. There are a lot of places in trace-cmd implementation with such checks.
The new libtracefs APIs can be used for this, they are ftarce instance aware:
 bool tracefs_file_exist(struct tracefs_instance *instance, char *name);
 bool tracefs_dir_exist(struct tracefs_instance *instance, char *name);

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 include/tracefs/tracefs.h      |  3 +++
 lib/tracefs/tracefs-instance.c | 49 +++++++++++++++++++++++++++++++++-
 2 files changed, 51 insertions(+), 1 deletion(-)

diff --git a/include/tracefs/tracefs.h b/include/tracefs/tracefs.h
index 85690b66..bc8bebcb 100644
--- a/include/tracefs/tracefs.h
+++ b/include/tracefs/tracefs.h
@@ -33,6 +33,9 @@ int tracefs_instance_file_write(struct tracefs_instance *instance,
 char *tracefs_instance_file_read(struct tracefs_instance *instance,
 				 char *file, int *psize);
 
+bool tracefs_file_exist(struct tracefs_instance *instance, char *name);
+bool tracefs_dir_exist(struct tracefs_instance *instance, char *name);
+
 /* events */
 void tracefs_list_free(char **list);
 char **tracefs_event_systems(const char *tracing_dir);
diff --git a/lib/tracefs/tracefs-instance.c b/lib/tracefs/tracefs-instance.c
index b96ab61c..67123e7c 100644
--- a/lib/tracefs/tracefs-instance.c
+++ b/lib/tracefs/tracefs-instance.c
@@ -13,7 +13,7 @@
 #include <errno.h>
 #include <sys/stat.h>
 #include <fcntl.h>
-
+#include <linux/limits.h>
 #include "tracefs.h"
 #include "tracefs-local.h"
 
@@ -247,3 +247,50 @@ char *tracefs_instance_file_read(struct tracefs_instance *instance,
 
 	return buf;
 }
+
+static bool check_file_exist(struct tracefs_instance *instance,
+			     char *name, bool dir)
+{
+	char file[PATH_MAX];
+	struct stat st;
+	char *path;
+	int ret;
+
+	path = tracefs_instance_get_dir(instance);
+	snprintf(file, PATH_MAX, "%s/%s", path, name);
+	tracefs_put_tracing_file(path);
+	ret = stat(file, &st);
+	if (ret < 0)
+		return false;
+
+	if (dir && !S_ISDIR(st.st_mode))
+		return false;
+	if (!dir && S_ISDIR(st.st_mode))
+		return false;
+
+	return true;
+}
+
+/**
+ * tracefs_file_exist - Check if a file with given name exists in given instance
+ * @instance: ftrace instance, can be NULL for the top instance
+ * @name: name of the file
+ *
+ * Returns true if the file exists, false otherwise
+ */
+bool tracefs_file_exist(struct tracefs_instance *instance, char *name)
+{
+	return check_file_exist(instance, name, false);
+}
+
+/**
+ * tracefs_dir_exist - Check if a directory with given name exists in given instance
+ * @instance: ftrace instance, can be NULL for the top instance
+ * @name: name of the directory
+ *
+ * Returns true if the directory exists, false otherwise
+ */
+bool tracefs_dir_exist(struct tracefs_instance *instance, char *name)
+{
+	return check_file_exist(instance, name, true);
+}
-- 
2.24.1