[PATCH 1/6] libtracefs: New APIs for opening and reading ftrace files

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

These new APIs can be used to read integer from frtace file and to open
ftrace file:
  tracefs_instance_file_read_int();
  tracefs_instance_file_open();

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 include/tracefs.h      |  6 ++++-
 src/tracefs-instance.c | 59 ++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 62 insertions(+), 3 deletions(-)

diff --git a/include/tracefs.h b/include/tracefs.h
index 3d70aca..460fa4c 100644
--- a/include/tracefs.h
+++ b/include/tracefs.h
@@ -29,7 +29,11 @@ char *tracefs_instance_get_dir(struct tracefs_instance *instance);
 int tracefs_instance_file_write(struct tracefs_instance *instance,
 				const char *file, const char *str);
 char *tracefs_instance_file_read(struct tracefs_instance *instance,
-				 char *file, int *psize);
+				 const char *file, int *psize);
+int tracefs_instance_file_read_int(struct tracefs_instance *instance,
+				   const char *file, long long *res);
+int tracefs_instance_file_open(struct tracefs_instance *instance,
+			       const char *file, int mode);
 int tracefs_instances_walk(int (*callback)(const char *, void *), void *context);
 
 bool tracefs_instance_exists(const char *name);
diff --git a/src/tracefs-instance.c b/src/tracefs-instance.c
index bf3de7c..27b9e99 100644
--- a/src/tracefs-instance.c
+++ b/src/tracefs-instance.c
@@ -14,7 +14,7 @@
 #include <sys/stat.h>
 #include <fcntl.h>
 #include <dirent.h>
-#include <linux/limits.h>
+#include <limits.h>
 #include "tracefs.h"
 #include "tracefs-local.h"
 
@@ -282,7 +282,7 @@ int tracefs_instance_file_write(struct tracefs_instance *instance,
  * The return string must be freed by free()
  */
 char *tracefs_instance_file_read(struct tracefs_instance *instance,
-				  char *file, int *psize)
+				 const char *file, int *psize)
 {
 	char *buf = NULL;
 	int size = 0;
@@ -301,6 +301,61 @@ char *tracefs_instance_file_read(struct tracefs_instance *instance,
 	return buf;
 }
 
+/**
+ * tracefs_instance_file_read_int - Read an integer from a trace file.
+ * @instance: ftrace instance, can be NULL for the top instance
+ * @file: name of the file
+ * @res: The integer from the file.
+ *
+ * Returns 0 if the reading is successful and the result is stored in res, -1
+ * in case of an error.
+ */
+int tracefs_instance_file_read_int(struct tracefs_instance *instance,
+				   const char *file, long long *res)
+{
+	long long ret = LLONG_MAX;
+	int size = 0;
+	char *str;
+
+	str = tracefs_instance_file_read(instance, file, &size);
+	if (size && str)
+		ret = strtoll(str, NULL, 0);
+	free(str);
+
+	if (LLONG_MIN == ret || LLONG_MAX == ret)
+		return -1;
+	*res = ret;
+	return 0;
+}
+
+/**
+ * tracefs_instance_file_open - Open a trace file for reading and writing
+ * @instance: ftrace instance, can be NULL for the top instance
+ * @file: name of the file
+ * @mode: file open flags, -1 for default O_RDWR
+ *
+ * Returns -1 in case of an error, or a valid file descriptor otherwise.
+ * The returned FD must be closed with close()
+ */
+int tracefs_instance_file_open(struct tracefs_instance *instance,
+			       const char *file, int mode)
+{
+	int flags = O_RDWR;
+	int fd = -1;
+	char *path;
+
+	path = tracefs_instance_get_file(instance, file);
+	if (!path)
+		return -1;
+
+	if (mode >= 0)
+		flags = mode;
+	fd = open(path, flags);
+	tracefs_put_tracing_file(path);
+
+	return fd;
+}
+
 static bool check_file_exists(struct tracefs_instance *instance,
 			     char *name, bool dir)
 {
-- 
2.29.2