wayland/dma-buf: Add meta_wayland_dma_buf_create_source

Creates a GSource which will call the specified dispatch callback when
all dma-buf file descriptors for the buffer have become readable.

v2:
* Hold a reference to the buffer in the source, to prevent the buffer
  from getting destroyed before the source.
v3:
* Do not use check callback, handle everything in dispatch callback.
  (Dor Askayo)
v4: (Georges Basile Stavracas Neto)
* Define and use MetaWaylandDmaBufSource & MetaWaylandDmaBufSourceDispatch
  types.
* Fix meta_wayland_dma_buf_source_dispatch &
  meta_wayland_dma_buf_source_funcs formatting.
* Use gpointer instead of void*.
* Rename meta_wayland_dma_buf_get_source to
  meta_wayland_dma_buf_create_source. (Carlos Garnacho)
v5:
* Explicitly handle NULL return value. (Jonas Ådahl)
v6:
* Fix style issue per check-style.py.
v7:
* Fix code style harder. (Jonas Ådahl)

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/1880>

src/wayland/meta-wayland-dma-buf.c

@@ -763,6 +763,153 @@ meta_wayland_dma_buf_from_buffer (MetaWaylandBuffer *buffer)
   return buffer->dma_buf.dma_buf;
 }
 
+typedef struct _MetaWaylandDmaBufSource
+{
+  GSource base;
+
+  MetaWaylandDmaBufSourceDispatch dispatch;
+  MetaWaylandBuffer *buffer;
+  gpointer user_data;
+
+  gpointer fd_tags[META_WAYLAND_DMA_BUF_MAX_FDS];
+} MetaWaylandDmaBufSource;
+
+static gboolean
+meta_wayland_dma_buf_fd_readable (int fd)
+{
+  GPollFD poll_fd;
+
+  poll_fd.fd = fd;
+  poll_fd.events = G_IO_IN;
+  poll_fd.revents = 0;
+
+  if (!g_poll (&poll_fd, 1, 0))
+    return FALSE;
+
+  return (poll_fd.revents & (G_IO_IN | G_IO_NVAL)) != 0;
+}
+
+static gboolean
+meta_wayland_dma_buf_source_dispatch (GSource     *base,
+                                      GSourceFunc  callback,
+                                      gpointer     user_data)
+{
+  MetaWaylandDmaBufSource *source;
+  MetaWaylandDmaBufBuffer *dma_buf;
+  gboolean ready;
+  uint32_t i;
+
+  source = (MetaWaylandDmaBufSource *) base;
+  dma_buf = source->buffer->dma_buf.dma_buf;
+  ready = TRUE;
+
+  for (i = 0; i < META_WAYLAND_DMA_BUF_MAX_FDS; i++)
+    {
+      gpointer fd_tag = source->fd_tags[i];
+
+      if (!fd_tag)
+        continue;
+
+      if (!meta_wayland_dma_buf_fd_readable (dma_buf->fds[i]))
+        {
+          ready = FALSE;
+          continue;
+        }
+
+      g_source_remove_unix_fd (&source->base, fd_tag);
+      source->fd_tags[i] = NULL;
+    }
+
+  if (!ready)
+    return G_SOURCE_CONTINUE;
+
+  source->dispatch (source->buffer, source->user_data);
+
+  return G_SOURCE_REMOVE;
+}
+
+static void
+meta_wayland_dma_buf_source_finalize (GSource *base)
+{
+  MetaWaylandDmaBufSource *source;
+  uint32_t i;
+
+  source = (MetaWaylandDmaBufSource *) base;
+
+  for (i = 0; i < META_WAYLAND_DMA_BUF_MAX_FDS; i++)
+    {
+      gpointer fd_tag = source->fd_tags[i];
+
+      if (fd_tag)
+        {
+          g_source_remove_unix_fd (&source->base, fd_tag);
+          source->fd_tags[i] = NULL;
+        }
+    }
+
+  g_clear_object (&source->buffer);
+}
+
+static GSourceFuncs meta_wayland_dma_buf_source_funcs = {
+  .dispatch = meta_wayland_dma_buf_source_dispatch,
+  .finalize = meta_wayland_dma_buf_source_finalize
+};
+
+/**
+ * meta_wayland_dma_buf_create_source:
+ * @buffer: A #MetaWaylandBuffer object
+ * @dispatch: Callback
+ * @user_data: User data for the callback
+ *
+ * Creates a GSource which will call the specified dispatch callback when all
+ * dma-buf file descriptors for the buffer have become readable.
+ *
+ * Returns: The new GSource (or
+ * %NULL if there are no dma-buf file descriptors, or they were all readable
+ * already)
+ */
+GSource *
+meta_wayland_dma_buf_create_source (MetaWaylandBuffer               *buffer,
+                                    MetaWaylandDmaBufSourceDispatch  dispatch,
+                                    gpointer                         user_data)
+{
+  MetaWaylandDmaBufBuffer *dma_buf;
+  MetaWaylandDmaBufSource *source = NULL;
+  uint32_t i;
+
+  dma_buf = buffer->dma_buf.dma_buf;
+  if (!dma_buf)
+    return NULL;
+
+  for (i = 0; i < META_WAYLAND_DMA_BUF_MAX_FDS; i++)
+    {
+      int fd = dma_buf->fds[i];
+
+      if (fd < 0)
+        break;
+
+      if (meta_wayland_dma_buf_fd_readable (fd))
+        continue;
+
+      if (!source)
+        {
+          source =
+            (MetaWaylandDmaBufSource *) g_source_new (&meta_wayland_dma_buf_source_funcs,
+                                                      sizeof (*source));
+          source->buffer = g_object_ref (buffer);
+          source->dispatch = dispatch;
+          source->user_data = user_data;
+        }
+
+      source->fd_tags[i] = g_source_add_unix_fd (&source->base, fd, G_IO_IN);
+    }
+
+  if (!source)
+    return NULL;
+
+  return &source->base;
+}
+
 static void
 buffer_params_create_common (struct wl_client   *client,
                              struct wl_resource *params_resource,

src/wayland/meta-wayland-dma-buf.h

@@ -57,6 +57,14 @@ meta_wayland_dma_buf_fds_for_wayland_buffer (MetaWaylandBuffer *buffer);
 MetaWaylandDmaBufBuffer *
 meta_wayland_dma_buf_from_buffer (MetaWaylandBuffer *buffer);
 
+typedef void (*MetaWaylandDmaBufSourceDispatch) (MetaWaylandBuffer *buffer,
+                                                 gpointer           user_data);
+
+GSource *
+meta_wayland_dma_buf_create_source (MetaWaylandBuffer               *buffer,
+                                    MetaWaylandDmaBufSourceDispatch  dispatch,
+                                    gpointer                         user_data);
+
 CoglScanout *
 meta_wayland_dma_buf_try_acquire_scanout (MetaWaylandDmaBufBuffer *dma_buf,
                                           CoglOnscreen            *onscreen);