allocators: Add DMABuf synchronization

When doing CPU Access, some architecture may require caches to be
synchronize before use. Otherwise, some visual artifact may be
visible, as the CPU modification may still resides in cache.

https://bugzilla.gnome.org/show_bug.cgi?id=794216

configure.ac

@@ -486,6 +486,9 @@ esac
 dnl Check for mmap (needed by allocators library)
 AC_CHECK_FUNC([mmap], [AC_DEFINE(HAVE_MMAP, 1, [Defined if mmap is supported])])
 
+dnl Check for DMABuf synchronization ioctl (needed for DMABuf CPU access)
+AC_CHECK_HEADERS([linux/dma-buf.h], [])
+
 dnl *** plug-ins to include ***
 
 dnl these are all the gst plug-ins, compilable without additional libs

gst-libs/gst/allocators/gstdmabuf.c

@@ -34,16 +34,67 @@
  * Since: 1.2
  */
 
-#ifdef HAVE_MMAP
-#include <sys/mman.h>
-#include <unistd.h>
+#ifdef HAVE_LINUX_DMA_BUF_H
+#include <sys/ioctl.h>
+#include <linux/dma-buf.h>
 #endif
 
 GST_DEBUG_CATEGORY_STATIC (dmabuf_debug);
 #define GST_CAT_DEFAULT dmabuf_debug
 
 G_DEFINE_TYPE (GstDmaBufAllocator, gst_dmabuf_allocator, GST_TYPE_FD_ALLOCATOR);
 
+static gpointer
+gst_dmabuf_mem_map (GstMemory * gmem, GstMapInfo * info, gsize maxsize)
+{
+  GstAllocator *allocator = gmem->allocator;
+#ifdef HAVE_LINUX_DMA_BUF_H
+  struct dma_buf_sync sync = { DMA_BUF_SYNC_START };
+  gpointer ret;
+
+  if (info->flags & GST_MAP_READ)
+    sync.flags |= DMA_BUF_SYNC_READ;
+
+  if (info->flags & GST_MAP_WRITE)
+    sync.flags |= DMA_BUF_SYNC_WRITE;
+#endif
+
+  ret = allocator->mem_map (gmem, maxsize, info->flags);
+
+#ifdef HAVE_LINUX_DMA_BUF_H
+  if (ret) {
+    if (ioctl (gst_fd_memory_get_fd (gmem), DMA_BUF_IOCTL_SYNC, &sync) < 0)
+      GST_WARNING_OBJECT (allocator, "Failed to synchronize DMABuf: %s (%i)",
+          g_strerror (errno), errno);
+  }
+#endif
+
+  return ret;
+}
+
+static void
+gst_dmabuf_mem_unmap (GstMemory * gmem, GstMapInfo * info)
+{
+  GstAllocator *allocator = gmem->allocator;
+#ifdef HAVE_LINUX_DMA_BUF_H
+  struct dma_buf_sync sync = { DMA_BUF_SYNC_END };
+
+  if (info->flags & GST_MAP_READ)
+    sync.flags |= DMA_BUF_SYNC_READ;
+
+  if (info->flags & GST_MAP_WRITE)
+    sync.flags |= DMA_BUF_SYNC_WRITE;
+
+  if (ioctl (gst_fd_memory_get_fd (gmem), DMA_BUF_IOCTL_SYNC, &sync) < 0)
+    GST_WARNING_OBJECT (allocator, "Failed to synchronize DMABuf: %s (%i)",
+        g_strerror (errno), errno);
+#else
+  GST_WARNING_OBJECT (allocator, "Using DMABuf without synchronization.");
+#endif
+
+  allocator->mem_unmap (gmem);
+}
+
 static void
 gst_dmabuf_allocator_class_init (GstDmaBufAllocatorClass * klass)
 {
@@ -55,6 +106,8 @@ gst_dmabuf_allocator_init (GstDmaBufAllocator * allocator)
   GstAllocator *alloc = GST_ALLOCATOR_CAST (allocator);
 
   alloc->mem_type = GST_ALLOCATOR_DMABUF;
+  alloc->mem_map_full = gst_dmabuf_mem_map;
+  alloc->mem_unmap_full = gst_dmabuf_mem_unmap;
 }
 
 /**

meson.build

@@ -79,6 +79,7 @@ check_headers = [
   ['HAVE_UNISTD_H', 'unistd.h'],
   ['HAVE_WINSOCK2_H', 'winsock2.h'],
   ['HAVE_XMMINTRIN_H', 'xmmintrin.h'],
+  ['HAVE_LINUX_DMA_BUF_H', 'linux/dma-buf.h'],
 ]
 foreach h : check_headers
   if cc.has_header(h.get(1))