v4l2codecs: Add remove buffers helpers

Add helpers function to call VIDIOC_REMOVE_BUFS ioctl.
If the driver support this feature buffers are removed from the queue when:
- the pool when is detached from the decoded.
- the pool is released.
- allocation failed.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/7684>

subprojects/gst-plugins-bad/sys/v4l2codecs/gstv4l2codecallocator.c

@@ -173,6 +173,7 @@ gst_v4l2_codec_allocator_prepare (GstV4l2CodecAllocator * self)
 {
   GstV4l2Decoder *decoder = self->decoder;
   GstPadDirection direction = self->direction;
+  GstV4l2CodecBuffer *buf;
   guint i;
 
   GST_DEBUG_OBJECT (self, "Try to create %d buffers", self->pool_size);
@@ -198,7 +199,16 @@ gst_v4l2_codec_allocator_prepare (GstV4l2CodecAllocator * self)
   return TRUE;
 
 failed:
+  /* If buffer allocation failed remove them all either by
+   * calling delete_buffers IOCTL if the driver support it,
+   * either by using legacy request_buf IOCTL with 0 has parameter */
+  if (gst_v4l2_decoder_has_remove_bufs (decoder)) {
+    while (i-- && (buf = g_queue_pop_tail (&self->pool))) {
+      gst_v4l2_decoder_remove_buffers (decoder, direction, buf->index, 1);
+    }
+  } else {
     gst_v4l2_decoder_request_buffers (decoder, direction, 0);
+  }
   return FALSE;
 }
 
@@ -212,10 +222,16 @@ static void
 gst_v4l2_codec_allocator_dispose (GObject * object)
 {
   GstV4l2CodecAllocator *self = GST_V4L2_CODEC_ALLOCATOR (object);
+  GstV4l2Decoder *decoder = self->decoder;
+  GstPadDirection direction = self->direction;
   GstV4l2CodecBuffer *buf;
 
-  while ((buf = g_queue_pop_head (&self->pool)))
+  while ((buf = g_queue_pop_head (&self->pool))) {
+    if (gst_v4l2_decoder_has_remove_bufs (decoder)) {
+      gst_v4l2_decoder_remove_buffers (decoder, direction, buf->index, 1);
+    }
     gst_v4l2_codec_buffer_free (buf);
+  }
 
   if (self->decoder) {
     gst_v4l2_codec_allocator_detach (self);
@@ -349,10 +365,21 @@ gst_v4l2_codec_allocator_get_pool_size (GstV4l2CodecAllocator * self)
 void
 gst_v4l2_codec_allocator_detach (GstV4l2CodecAllocator * self)
 {
+  GstV4l2Decoder *decoder = self->decoder;
+
   GST_OBJECT_LOCK (self);
   if (!self->detached) {
     self->detached = TRUE;
+    if (!gst_v4l2_decoder_has_remove_bufs (decoder)) {
       gst_v4l2_decoder_request_buffers (self->decoder, self->direction, 0);
+    } else {
+      GstV4l2CodecBuffer *buf;
+
+      while ((buf = g_queue_pop_tail (&self->pool)))
+        gst_v4l2_decoder_remove_buffers (self->decoder, self->direction,
+            buf->index, 1);
+
+    }
   }
   GST_OBJECT_UNLOCK (self);
 }

subprojects/gst-plugins-bad/sys/v4l2codecs/gstv4l2decoder.c

@@ -78,6 +78,7 @@ struct _GstV4l2Decoder
   GstVecDeque *request_pool;
   GstVecDeque *pending_requests;
   guint version;
+  GstVideoInfo *info;
 
   enum v4l2_buf_type src_buf_type;
   enum v4l2_buf_type sink_buf_type;
@@ -90,6 +91,7 @@ struct _GstV4l2Decoder
 
   /* detected features */
   gboolean supports_holding_capture;
+  gboolean supports_remove_buffers;
 };
 
 G_DEFINE_TYPE_WITH_CODE (GstV4l2Decoder, gst_v4l2_decoder, GST_TYPE_OBJECT,
@@ -225,6 +227,11 @@ gst_v4l2_decoder_open (GstV4l2Decoder * self)
     return FALSE;
   }
 
+  if (createbufs.capabilities & V4L2_BUF_CAP_SUPPORTS_REMOVE_BUFS)
+    self->supports_remove_buffers = TRUE;
+  else
+    self->supports_remove_buffers = FALSE;
+
   self->opened = TRUE;
 
   return TRUE;
@@ -550,6 +557,31 @@ gst_v4l2_decoder_enum_src_formats (GstV4l2Decoder * self,
   return caps;
 }
 
+gboolean
+gst_v4l2_decoder_remove_buffers (GstV4l2Decoder * self,
+    GstPadDirection direction, guint index, guint num_buffers)
+{
+  gint ret;
+  struct v4l2_remove_buffers remove_bufs = {
+    .type = direction_to_buffer_type (self, direction),
+    .index = index,
+    .count = num_buffers,
+  };
+
+  if (!self->supports_remove_buffers)
+    return FALSE;
+
+  GST_DEBUG_OBJECT (self, "remove buffers %d from index %d", remove_bufs.count,
+      remove_bufs.index);
+  ret = ioctl (self->video_fd, VIDIOC_REMOVE_BUFS, &remove_bufs);
+  if (ret < 0) {
+    GST_ERROR_OBJECT (self, "VIDIOC_REMOVE_BUF failed: %s", g_strerror (errno));
+    return FALSE;
+  }
+
+  return TRUE;
+}
+
 gboolean
 gst_v4l2_decoder_select_src_format (GstV4l2Decoder * self, GstCaps * caps,
     GstVideoInfo * vinfo, GstVideoInfoDmaDrm * vinfo_drm)
@@ -1233,6 +1265,19 @@ gst_v4l2_decoder_get_render_delay (GstV4l2Decoder * self)
   return self->render_delay;
 }
 
+/**
+ * gst_v4l2_decoder_has_remove_bufs:
+ * @self: a #GstV4l2Decoder pointer
+ *
+ * Returns: TRUE if the video decoder driver allows to remove
+ * buffers from CAPTURE queue.
+ */
+gboolean
+gst_v4l2_decoder_has_remove_bufs (GstV4l2Decoder * self)
+{
+  return self->supports_remove_buffers;
+}
+
 GstV4l2Request *
 gst_v4l2_request_ref (GstV4l2Request * request)
 {

subprojects/gst-plugins-bad/sys/v4l2codecs/gstv4l2decoder.h

@@ -90,6 +90,11 @@ gint              gst_v4l2_decoder_create_buffers (GstV4l2Decoder * self,
                                                    GstPadDirection direction,
 						   guint num_buffers);
 
+gint              gst_v4l2_decoder_remove_buffers (GstV4l2Decoder * self,
+		                                   GstPadDirection direction,
+                                                   guint index,
+						   guint num_buffers);
+
 gboolean          gst_v4l2_decoder_export_buffer (GstV4l2Decoder * self,
                                                   GstPadDirection directon,
                                                   gint index,
@@ -145,6 +150,7 @@ void              gst_v4l2_decoder_set_render_delay (GstV4l2Decoder * self,
 
 guint             gst_v4l2_decoder_get_render_delay (GstV4l2Decoder * self);
 
+gboolean	  gst_v4l2_decoder_has_remove_bufs (GstV4l2Decoder * self);
 
 GstV4l2Request *  gst_v4l2_request_ref (GstV4l2Request * request);