v4l2: Add support for querying capabilities

This adds a helper function to query v4l2 capabilities, returning
either the device caps when available or the general device caps
otherwise.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>

src/v4l2.c

@@ -32,6 +32,27 @@
 #include "utils.h"
 #include "v4l2.h"
 
+int v4l2_query_capabilities(int video_fd, unsigned int *capabilities)
+{
+	struct v4l2_capability capability;
+	int rc;
+
+	memset(&capability, 0, sizeof(capability));
+
+	rc = ioctl(video_fd, VIDIOC_QUERYCAP, &capability);
+	if (rc < 0)
+		return -1;
+
+	if (capabilities != NULL) {
+		if ((capability.capabilities & V4L2_CAP_DEVICE_CAPS) != 0)
+			*capabilities = capability.device_caps;
+		else
+			*capabilities = capability.capabilities;
+	}
+
+	return 0;
+}
+
 bool v4l2_find_format(int video_fd, unsigned int type, unsigned int pixelformat)
 {
 	struct v4l2_fmtdesc fmtdesc;

src/v4l2.h

@@ -29,6 +29,7 @@
 
 #define SOURCE_SIZE_MAX						(1024 * 1024)
 
+int v4l2_query_capabilities(int video_fd, unsigned int *capabilities);
 bool v4l2_find_format(int video_fd, unsigned int type,
 		      unsigned int pixelformat);
 int v4l2_set_format(int video_fd, unsigned int type, unsigned int pixelformat,