v4l2codecs: Replace VIDIOC_REQBUFS calls by VIDIOC_CREATE_BUFS

Use VIDIOC_CREATE_BUFS ioctl to create buffers instead of VIDIOC_REQBUFS
because it allows to create buffers also while streaming.
To prepare the introduction of VIDIOC_REMOVE_BUFFERS create
the buffers one per one instead of a range of them. This way
it can, in the futur, fill the holes.
gst_v4l2_decoder_request_buffers() is stil used to remove all
the buffers of the queue.

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

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

@@ -173,21 +173,25 @@ gst_v4l2_codec_allocator_prepare (GstV4l2CodecAllocator * self)
 {
   GstV4l2Decoder *decoder = self->decoder;
   GstPadDirection direction = self->direction;
-  gint ret;
   guint i;
 
-  ret = gst_v4l2_decoder_request_buffers (decoder, direction, self->pool_size);
-  if (ret < self->pool_size) {
-    if (ret >= 0)
+  GST_DEBUG_OBJECT (self, "Try to create %d buffers", self->pool_size);
+
+  /* Allocate buffers one by one to avoid fragmentation issue and
+   * use the possible holes in v4l2 queue array */
+  for (i = 0; i < self->pool_size; i++) {
+    GstV4l2CodecBuffer *buf;
+    gint index = gst_v4l2_decoder_create_buffers (decoder, direction, 1);
+    if (index < 0) {
       GST_ERROR_OBJECT (self,
           "%i buffer was needed, but only %i could be allocated",
-          self->pool_size, ret);
-    goto failed;
-  }
+          self->pool_size, i);
+      goto failed;
+    }
 
-  for (i = 0; i < self->pool_size; i++) {
-    GstV4l2CodecBuffer *buf = gst_v4l2_codec_buffer_new (GST_ALLOCATOR (self),
-        decoder, direction, i);
+    buf =
+        gst_v4l2_codec_buffer_new (GST_ALLOCATOR (self), decoder, direction,
+        index);
     g_queue_push_tail (&self->pool, buf);
   }
 

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

@@ -659,14 +659,43 @@ gst_v4l2_decoder_request_buffers (GstV4l2Decoder * self,
     return ret;
   }
 
+  return reqbufs.count;
+}
+
+gint
+gst_v4l2_decoder_create_buffers (GstV4l2Decoder * self,
+    GstPadDirection direction, guint num_buffers)
+{
+  gint ret;
+  struct v4l2_create_buffers createbufs = {
+    .count = num_buffers,
+    .memory = V4L2_MEMORY_MMAP,
+    .format.type = direction_to_buffer_type (self, direction),
+  };
+
+  GST_DEBUG_OBJECT (self, "Creating %u buffers", num_buffers);
+
+  ret = ioctl (self->video_fd, VIDIOC_G_FMT, &createbufs.format);
+  if (ret < 0) {
+    GST_ERROR_OBJECT (self, "VIDIOC_G_FMT failed: %s", g_strerror (errno));
+    return ret;
+  }
+
+  ret = ioctl (self->video_fd, VIDIOC_CREATE_BUFS, &createbufs);
+  if (ret < 0) {
+    GST_ERROR_OBJECT (self, "VIDIOC_CREATE_BUFS failed: %s",
+        g_strerror (errno));
+    return ret;
+  }
+
   if (direction == GST_PAD_SINK) {
-    if (reqbufs.capabilities & V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF)
+    if (createbufs.capabilities & V4L2_BUF_CAP_SUPPORTS_M2M_HOLD_CAPTURE_BUF)
       self->supports_holding_capture = TRUE;
     else
       self->supports_holding_capture = FALSE;
   }
 
-  return reqbufs.count;
+  return createbufs.index;
 }
 
 gboolean

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

@@ -86,6 +86,10 @@ gint              gst_v4l2_decoder_request_buffers (GstV4l2Decoder * self,
                                                     GstPadDirection direction,
                                                     guint num_buffers);
 
+gint              gst_v4l2_decoder_create_buffers (GstV4l2Decoder * self,
+                                                   GstPadDirection direction,
+						   guint num_buffers);
+
 gboolean          gst_v4l2_decoder_export_buffer (GstV4l2Decoder * self,
                                                   GstPadDirection directon,
                                                   gint index,