[PATCH 2/2] trace-cmd: Add new API tracecmd_open_head()

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

Add an API to create a tracecmd_handle from a file,
read and parse only the trace headers from the file.
This allows to implement opening a trace file on
stages - reading the trace headers and reading the trace data.

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 include/trace-cmd/trace-cmd.h |  1 +
 lib/trace-cmd/trace-input.c   | 28 ++++++++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/include/trace-cmd/trace-cmd.h b/include/trace-cmd/trace-cmd.h
index 3f96bbde..e22aa251 100644
--- a/include/trace-cmd/trace-cmd.h
+++ b/include/trace-cmd/trace-cmd.h
@@ -143,6 +143,7 @@ typedef void (*tracecmd_handle_init_func)(struct tracecmd_input *handle,
 struct tracecmd_input *tracecmd_alloc(const char *file);
 struct tracecmd_input *tracecmd_alloc_fd(int fd);
 struct tracecmd_input *tracecmd_open(const char *file);
+struct tracecmd_input *tracecmd_open_head(const char *file);
 struct tracecmd_input *tracecmd_open_fd(int fd);
 void tracecmd_ref(struct tracecmd_input *handle);
 void tracecmd_close(struct tracecmd_input *handle);
diff --git a/lib/trace-cmd/trace-input.c b/lib/trace-cmd/trace-input.c
index ee9bfb52..efc8d4bd 100644
--- a/lib/trace-cmd/trace-input.c
+++ b/lib/trace-cmd/trace-input.c
@@ -3175,6 +3175,34 @@ struct tracecmd_input *tracecmd_open(const char *file)
 	return tracecmd_open_fd(fd);
 }
 
+/**
+ * tracecmd_open_head - create a tracecmd_handle from a given file, read
+ *			read and parse only the trace headers from the file
+ * @file: the file name of the file that is of tracecmd data type.
+ */
+struct tracecmd_input *tracecmd_open_head(const char *file)
+{
+	struct tracecmd_input *handle;
+	int fd;
+
+	fd = open(file, O_RDONLY);
+	if (fd < 0)
+		return NULL;
+
+	handle = tracecmd_alloc_fd(fd);
+	if (!handle)
+		return NULL;
+
+	if (tracecmd_read_headers(handle) < 0)
+		goto fail;
+
+	return handle;
+
+fail:
+	tracecmd_close(handle);
+	return NULL;
+}
+
 /**
  * tracecmd_ref - add a reference to the handle
  * @handle: input handle for the trace.dat file
-- 
2.25.1