cam: Allow specifying directories in the --file option

The value of the --file option is the full name of the file to which
captured frames are written. To write files to a specific directory with
the default naming scheme, the "frame-#.bin" name has to appear at the
end of the file name. Simplify usage of the option by allowing --file to
specify a directory only. If the file name ends with a '/', the default
"frame-#.bin" file name is automatically appended.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

src/cam/buffer_writer.cpp

@@ -49,7 +49,12 @@ int BufferWriter::write(FrameBuffer *buffer, const std::string &streamName)
 	size_t pos;
 	int fd, ret = 0;
 
+	if (!pattern_.empty())
 		filename = pattern_;
+
+	if (filename.empty() || filename.back() == '/')
+		filename += "frame-#.bin";
+
 	pos = filename.find_first_of('#');
 	if (pos != std::string::npos) {
 		std::stringstream ss;

src/cam/buffer_writer.h

@@ -15,7 +15,7 @@
 class BufferWriter
 {
 public:
-	BufferWriter(const std::string &pattern = "frame-#.bin");
+	BufferWriter(const std::string &pattern = "");
 	~BufferWriter();
 
 	void mapBuffer(libcamera::FrameBuffer *buffer);

src/cam/main.cpp

@@ -118,7 +118,10 @@ int CamApp::parseOptions(int argc, char *argv[])
 			 "capture", ArgumentOptional, "count");
 	parser.addOption(OptFile, OptionString,
 			 "Write captured frames to disk\n"
-			 "The first '#' character in the file name is expanded to the stream name and frame sequence number.\n"
+			 "If the file name ends with a '/', it sets the directory in which\n"
+			 "to write files, using the default file name. Otherwise it sets the\n"
+			 "full file path and name. The first '#' character in the file name\n"
+			 "is expanded to the stream name and frame sequence number.\n"
 			 "The default file name is 'frame-#.bin'.",
 			 "file", ArgumentOptional, "filename");
 	parser.addOption(OptStream, &streamKeyValue,