[PATCH v2 3/7] libtracefs: New APIs for enable / disable tracing

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

These new APIs can be used to enable / disable tracing in given ftrace
instance:
  tracefs_trace_is_on();
  tracefs_trace_on();
  tracefs_trace_off();
  tracefs_trace_on_get_fd();
  tracefs_trace_on_fd();
  tracefs_trace_off_fd();

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 include/tracefs.h   |  18 ++++++++
 src/Makefile        |   1 +
 src/tracefs-tools.c | 109 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 128 insertions(+)
 create mode 100644 src/tracefs-tools.c

diff --git a/include/tracefs.h b/include/tracefs.h
index bec8369..85a776e 100644
--- a/include/tracefs.h
+++ b/include/tracefs.h
@@ -40,6 +40,24 @@ bool tracefs_instance_exists(const char *name);
 bool tracefs_file_exists(struct tracefs_instance *instance, char *name);
 bool tracefs_dir_exists(struct tracefs_instance *instance, char *name);
 
+int tracefs_trace_is_on(struct tracefs_instance *instance);
+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);
+
+/**
+ * tracefs_trace_on_get_fd - Get a file descriptor of "tracing_on" in given instance
+ * @instance: ftrace instance, can be NULL for the top instance
+ *
+ * Returns -1 in case of an error, or a valid file descriptor to "tracing_on"
+ * file for reading and writing.The returned FD must be closed with close().
+ */
+static inline int tracefs_trace_on_get_fd(struct tracefs_instance *instance)
+{
+	return tracefs_instance_file_open(instance, "tracing_on", O_RDWR);
+}
+
 /* events */
 void tracefs_list_free(char **list);
 char **tracefs_event_systems(const char *tracing_dir);
diff --git a/src/Makefile b/src/Makefile
index 3f64905..dabdbb4 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -6,6 +6,7 @@ OBJS =
 OBJS += tracefs-utils.o
 OBJS += tracefs-instance.o
 OBJS += tracefs-events.o
+OBJS += tracefs-tools.o
 
 OBJS := $(OBJS:%.o=$(bdir)/%.o)
 DEPS := $(OBJS:$(bdir)/%.o=$(bdir)/.%.d)
diff --git a/src/tracefs-tools.c b/src/tracefs-tools.c
new file mode 100644
index 0000000..101f389
--- /dev/null
+++ b/src/tracefs-tools.c
@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: LGPL-2.1
+/*
+ * Copyright (C) 2008, 2009, 2010 Red Hat Inc, Steven Rostedt <srostedt@redhat.com>
+ *
+ * Updates:
+ * Copyright (C) 2021, VMware, Tzvetomir Stoyanov <tz.stoyanov@gmail.com>
+ *
+ */
+#include <stdlib.h>
+#include <unistd.h>
+#include <fcntl.h>
+
+#include "tracefs.h"
+#include "tracefs-local.h"
+
+#define TRACE_CTRL	"tracing_on"
+
+static int trace_on_off(int fd, bool on)
+{
+	const char *val = on ? "1" : "0";
+	int ret;
+
+	ret = write(fd, val, 1);
+	if (ret == 1)
+		return 0;
+
+	return -1;
+}
+
+static int trace_on_off_file(struct tracefs_instance *instance, bool on)
+{
+	int ret;
+	int fd;
+
+	fd = tracefs_instance_file_open(instance, TRACE_CTRL, O_WRONLY);
+	if (fd < 0)
+		return -1;
+	ret = trace_on_off(fd, on);
+	close(fd);
+
+	return ret;
+}
+
+/**
+ * tracefs_trace_is_on - Check if writing traces to the ring buffer is enabled
+ * @instance: ftrace instance, can be NULL for the top instance
+ *
+ * Returns -1 in case of an error, 0 if tracing is disable or 1 if tracing
+ * is enabled.
+ */
+int tracefs_trace_is_on(struct tracefs_instance *instance)
+{
+	long long res;
+
+	if (tracefs_instance_file_read_number(instance, TRACE_CTRL, &res) == 0)
+		return (int)res;
+
+	return -1;
+}
+
+/**
+ * tracefs_trace_on - Enable writing traces to the ring buffer of the given instance
+ * @instance: ftrace instance, can be NULL for the top instance
+ *
+ * Returns -1 in case of an error or 0 otherwise
+ */
+int tracefs_trace_on(struct tracefs_instance *instance)
+{
+	return trace_on_off_file(instance, true);
+}
+
+/**
+ * tracefs_trace_off - Disable writing traces to the ring buffer of the given instance
+ * @instance: ftrace instance, can be NULL for the top instance
+ *
+ * Returns -1 in case of an error or 0 otherwise
+ */
+int tracefs_trace_off(struct tracefs_instance *instance)
+{
+	return trace_on_off_file(instance, false);
+}
+
+/**
+ * tracefs_trace_on_fd - Enable writing traces to the ring buffer
+ * @fd: File descriptor to ftrace tracing_on file, previously opened
+ *	with tracefs_trace_on_get_fd()
+ *
+ * Returns -1 in case of an error or 0 otherwise
+ */
+int tracefs_trace_on_fd(int fd)
+{
+	if (fd < 0)
+		return -1;
+	return trace_on_off(fd, true);
+}
+
+/**
+ * tracefs_trace_off_fd - Disable writing traces to the ring buffer
+ * @fd: File descriptor to ftrace tracing_on file, previously opened
+ *	with tracefs_trace_on_get_fd()
+ *
+ * Returns -1 in case of an error or 0 otherwise
+ */
+int tracefs_trace_off_fd(int fd)
+{
+	if (fd < 0)
+		return -1;
+	return trace_on_off(fd, false);
+}
-- 
2.29.2