v4l2codecs: h264: Add API checks

Check that the V4L2 H264 controls' sizes match
our expectation. If not, then probably there's an API
mismatch which will cause errors or decoding corruption.

Also, print a warning if the kernel version is too old.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gst-plugins-bad/-/merge_requests/1624>

sys/v4l2codecs/gstv4l2codech264dec.c

@@ -26,6 +26,12 @@
 #include "gstv4l2codecpool.h"
 #include "linux/v4l2-controls.h"
 
+#define KERNEL_VERSION(a,b,c) (((a) << 16) + ((b) << 8) + (c))
+
+#define V4L2_MIN_KERNEL_VER_MAJOR 5
+#define V4L2_MIN_KERNEL_VER_MINOR 11
+#define V4L2_MIN_KERNEL_VERSION KERNEL_VERSION(V4L2_MIN_KERNEL_VER_MAJOR, V4L2_MIN_KERNEL_VER_MINOR, 0)
+
 GST_DEBUG_CATEGORY_STATIC (v4l2_h264dec_debug);
 #define GST_CAT_DEFAULT v4l2_h264dec_debug
 
@@ -109,10 +115,62 @@ needs_start_codes (GstV4l2CodecH264Dec * self)
 }
 
 
+static gboolean
+gst_v4l2_decoder_h264_api_check (GstV4l2CodecH264Dec * self)
+{
+  guint i, ret_size;
+  /* *INDENT-OFF* */
+  struct
+  {
+    unsigned int id;
+    unsigned int size;
+  } controls[] = {
+    {
+      .id = V4L2_CID_MPEG_VIDEO_H264_SPS,
+      .size = sizeof(struct v4l2_ctrl_h264_sps),
+    }, {
+      .id = V4L2_CID_MPEG_VIDEO_H264_PPS,
+      .size = sizeof(struct v4l2_ctrl_h264_pps),
+    }, {
+      .id = V4L2_CID_MPEG_VIDEO_H264_SCALING_MATRIX,
+      .size = sizeof(struct v4l2_ctrl_h264_scaling_matrix),
+    }, {
+      .id = V4L2_CID_MPEG_VIDEO_H264_DECODE_PARAMS,
+      .size = sizeof(struct v4l2_ctrl_h264_decode_params),
+    }, {
+      .id = V4L2_CID_MPEG_VIDEO_H264_SLICE_PARAMS,
+      .size = sizeof(struct v4l2_ctrl_h264_slice_params),
+    }, {
+      .id = V4L2_CID_MPEG_VIDEO_H264_PRED_WEIGHTS,
+      .size = sizeof(struct v4l2_ctrl_h264_pred_weights),
+    }
+  };
+  /* *INDENT-ON* */
+
+  /*
+   * Compatibility check: make sure the pointer controls are
+   * the right size.
+   */
+  for (i = 0; i < G_N_ELEMENTS (controls); i++) {
+    if (gst_v4l2_decoder_query_control_size (self->decoder, controls[i].id,
+            &ret_size) && ret_size != controls[i].size) {
+      GST_ELEMENT_ERROR (self, RESOURCE, OPEN_READ_WRITE,
+          ("H264 API mismatch!"),
+          ("%d control size mismatch: got %d bytes but %d expected.",
+              controls[i].id, ret_size, controls[i].size));
+      return FALSE;
+    }
+  }
+
+  return TRUE;
+}
+
 static gboolean
 gst_v4l2_codec_h264_dec_open (GstVideoDecoder * decoder)
 {
   GstV4l2CodecH264Dec *self = GST_V4L2_CODEC_H264_DEC (decoder);
+  guint version;
+
   /* *INDENT-OFF* */
   struct v4l2_ext_control control[] = {
     {
@@ -131,6 +189,20 @@ gst_v4l2_codec_h264_dec_open (GstVideoDecoder * decoder)
     return FALSE;
   }
 
+  version = gst_v4l2_decoder_get_version (self->decoder);
+  if (version < V4L2_MIN_KERNEL_VERSION)
+    GST_WARNING_OBJECT (self,
+        "V4L2 API v%u.%u too old, at least v%u.%u required",
+        (version >> 16) & 0xff, (version >> 8) & 0xff,
+        V4L2_MIN_KERNEL_VER_MAJOR, V4L2_MIN_KERNEL_VER_MINOR);
+
+  if (!gst_v4l2_decoder_h264_api_check (self)) {
+    GST_ELEMENT_ERROR (self, RESOURCE, OPEN_READ_WRITE,
+        ("Failed to open H264 decoder"),
+        ("gst_v4l2_decoder_h264_api_check() failed"));
+    return FALSE;
+  }
+
   if (!gst_v4l2_decoder_get_controls (self->decoder, control,
           G_N_ELEMENTS (control))) {
     GST_ELEMENT_ERROR (self, RESOURCE, OPEN_READ_WRITE,

sys/v4l2codecs/gstv4l2decoder.c

@@ -74,6 +74,7 @@ struct _GstV4l2Decoder
   gint video_fd;
   GstQueueArray *request_pool;
   GstQueueArray *pending_requests;
+  guint version;
 
   enum v4l2_buf_type src_buf_type;
   enum v4l2_buf_type sink_buf_type;
@@ -148,6 +149,12 @@ gst_v4l2_decoder_new (GstV4l2CodecDevice * device)
   return gst_object_ref_sink (decoder);
 }
 
+guint
+gst_v4l2_decoder_get_version (GstV4l2Decoder * self)
+{
+  return self->version;
+}
+
 gboolean
 gst_v4l2_decoder_open (GstV4l2Decoder * self)
 {
@@ -176,6 +183,8 @@ gst_v4l2_decoder_open (GstV4l2Decoder * self)
     return FALSE;
   }
 
+  self->version = querycap.version;
+
   if (querycap.capabilities & V4L2_CAP_DEVICE_CAPS)
     capabilities = querycap.device_caps;
   else
@@ -717,6 +726,29 @@ gst_v4l2_decoder_get_controls (GstV4l2Decoder * self,
   return TRUE;
 }
 
+gboolean
+gst_v4l2_decoder_query_control_size (GstV4l2Decoder * self,
+    unsigned int control_id, unsigned int *control_size)
+{
+  gint ret;
+  struct v4l2_query_ext_ctrl control = {
+    .id = control_id,
+  };
+
+  *control_size = 0;
+
+  ret = ioctl (self->video_fd, VIDIOC_QUERY_EXT_CTRL, &control);
+  if (ret < 0)
+    /*
+     * It's not an error if a control is not supported by this driver.
+     * Return false but don't print any error.
+     */
+    return FALSE;
+
+  *control_size = control.elem_size;
+  return TRUE;
+}
+
 void
 gst_v4l2_decoder_install_properties (GObjectClass * gobject_class,
     gint prop_offset, GstV4l2CodecDevice * device)

sys/v4l2codecs/gstv4l2decoder.h

@@ -35,6 +35,8 @@ typedef struct _GstV4l2Request GstV4l2Request;
 
 GstV4l2Decoder *  gst_v4l2_decoder_new (GstV4l2CodecDevice * device);
 
+guint             gst_v4l2_decoder_get_version (GstV4l2Decoder * self);
+
 gboolean          gst_v4l2_decoder_open (GstV4l2Decoder * decoder);
 
 gboolean          gst_v4l2_decoder_close (GstV4l2Decoder * decoder);
@@ -81,6 +83,10 @@ gboolean          gst_v4l2_decoder_get_controls (GstV4l2Decoder * self,
                                                  struct v4l2_ext_control * control,
                                                  guint count);
 
+gboolean          gst_v4l2_decoder_query_control_size (GstV4l2Decoder * self,
+                                                 unsigned int control_id,
+						 unsigned int *control_size);
+
 void              gst_v4l2_decoder_install_properties (GObjectClass * gobject_class,
                                                        gint prop_offset,
                                                        GstV4l2CodecDevice * device);