[PATCH 06/20] trace-cmd library: Write compression header in the trace file

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

If there is a compression configured on the output file handler and if
the file version is at least 7, write compression header in the file.
The compression header is two null terminated strings - name and version
of the compression algorithm, used to compress some parts of the file.
The header is located after the page size in the file. The new header is
mandatory for trace files version 7. If no compression is used, the
string "none" is saved as name of the compression algorithm and empty
string as compression algorithm version.

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 lib/trace-cmd/trace-output.c | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

diff --git a/lib/trace-cmd/trace-output.c b/lib/trace-cmd/trace-output.c
index 802d35ed..c979a6ed 100644
--- a/lib/trace-cmd/trace-output.c
+++ b/lib/trace-cmd/trace-output.c
@@ -1076,6 +1076,24 @@ out_free:
 	return ret;
 }
 
+static int write_compression_header(struct tracecmd_output *handle)
+{
+	const char *name = NULL;
+	const char *ver = NULL;
+	int ret;
+
+	ret = tracecmd_compress_proto_get_name(handle->compress, &name, &ver);
+	if (ret < 0 || !name || !ver) {
+		name = "none";
+		ver = "";
+	}
+	if (do_write_check(handle, name, strlen(name) + 1))
+		return -1;
+	if (do_write_check(handle, ver, strlen(ver) + 1))
+		return -1;
+	return 0;
+}
+
 /**
  * tracecmd_output_allocate - allocate new output handler to a trace file
  * @handle: file descriptor to an empty file, it can be -1 if the handler
@@ -1362,6 +1380,10 @@ int tracecmd_output_write_init(struct tracecmd_output *handler)
 	endian4 = convert_endian_4(handler, handler->page_size);
 	if (do_write_check(handler, &endian4, 4))
 		return -1;
+	if (handler->file_version >= FILE_VERSION_COMPRESSION) {
+		if (write_compression_header(handler))
+			return -1;
+	}
 	if (HAS_SECTIONS(handler)) {
 		/* Write 0 as options offset and save its location */
 		offset = 0;
-- 
2.31.1