[PATCH 8/9] libcamera: v4l2_subdevice: Replace Routing::toString() with operator<<()

[Laurent Pinchart]

The main (and only at the moment) use case for the Routing::toString()
function is to print a representation of the routing table in a log
message. The function is implemented using an std::stringstream, and the
returned std::string is then inserted into an std::ostream. This is
inefficient. Replace the function with a specialization of the
operator<<() and use it in the caller.

Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
---
 include/libcamera/internal/v4l2_subdevice.h |  7 ++---
 src/libcamera/pipeline/simple/simple.cpp    |  2 +-
 src/libcamera/v4l2_subdevice.cpp            | 29 +++++++++++----------
 3 files changed, 18 insertions(+), 20 deletions(-)

diff --git a/include/libcamera/internal/v4l2_subdevice.h b/include/libcamera/internal/v4l2_subdevice.h
index 65003394a984..2f64b3deadfe 100644
--- a/include/libcamera/internal/v4l2_subdevice.h
+++ b/include/libcamera/internal/v4l2_subdevice.h
@@ -85,11 +85,7 @@ public:
 		unsigned int stream;
 	};
 
-	class Routing : public std::vector<struct v4l2_subdev_route>
-	{
-	public:
-		std::string toString() const;
-	};
+	using Routing = std::vector<struct v4l2_subdev_route>;
 
 	explicit V4L2Subdevice(const MediaEntity *entity);
 	~V4L2Subdevice();
@@ -161,5 +157,6 @@ private:
 };
 
 std::ostream &operator<<(std::ostream &out, const V4L2Subdevice::Stream &stream);
+std::ostream &operator<<(std::ostream &out, const V4L2Subdevice::Routing &routing);
 
 } /* namespace libcamera */
diff --git a/src/libcamera/pipeline/simple/simple.cpp b/src/libcamera/pipeline/simple/simple.cpp
index 1145e80847ba..1dbbd7fe91d6 100644
--- a/src/libcamera/pipeline/simple/simple.cpp
+++ b/src/libcamera/pipeline/simple/simple.cpp
@@ -1387,7 +1387,7 @@ int SimplePipelineHandler::resetRoutingTable(V4L2Subdevice *subdev)
 
 	LOG(SimplePipeline, Debug)
 		<< "Routing table of " << subdev->deviceNode()
-		<< " reset to " << routing.toString();
+		<< " reset to " << routing;
 
 	return 0;
 }
diff --git a/src/libcamera/v4l2_subdevice.cpp b/src/libcamera/v4l2_subdevice.cpp
index efe8b0f793e9..1670c31a9656 100644
--- a/src/libcamera/v4l2_subdevice.cpp
+++ b/src/libcamera/v4l2_subdevice.cpp
@@ -844,30 +844,31 @@ std::ostream &operator<<(std::ostream &out, const V4L2Subdevice::Stream &stream)
 }
 
 /**
- * \class V4L2Subdevice::Routing
+ * \typedef V4L2Subdevice::Routing
  * \brief V4L2 subdevice routing table
  *
  * This class stores a subdevice routing table as a vector of routes.
  */
 
 /**
- * \brief Assemble and return a string describing the routing table
- * \return A string describing the routing table
+ * \brief Insert a text representation of a V4L2Subdevice::Routing into an
+ *	output stream
+ * \param[in] out The output stream
+ * \param[in] routing The V4L2Subdevice::Routing
+ * \return The output stream \a out
  */
-std::string V4L2Subdevice::Routing::toString() const
+std::ostream &operator<<(std::ostream &out, const V4L2Subdevice::Routing &routing)
 {
-	std::stringstream routing;
-
-	for (const auto &[i, route] : utils::enumerate(*this)) {
-		routing << "[" << i << "] "
-			<< route.sink_pad << "/" << route.sink_stream << " -> "
-			<< route.source_pad << "/" << route.source_stream
-			<< " (" << utils::hex(route.flags) << ")";
-		if (i != size() - 1)
-			routing << ", ";
+	for (const auto &[i, route] : utils::enumerate(routing)) {
+		out << "[" << i << "] "
+		    << route.sink_pad << "/" << route.sink_stream << " -> "
+		    << route.source_pad << "/" << route.source_stream
+		    << " (" << utils::hex(route.flags) << ")";
+		if (i != routing.size() - 1)
+			out << ", ";
 	}
 
-	return routing.str();
+	return out;
 }
 
 /**
-- 
Regards,

Laurent Pinchart