From: Giovanni Campagna <gcampa...@src.gnome.org>

Turn GBM into a swrast loader (providing putimage/getimage backed
by a dumb KMS buffer). This allows to run KMS+DRM GL applications
(such as weston or mutter-wayland) unmodified on cards that don't
have any client side HW acceleration component but that can do
modeset (examples include simpledrm and qxl)
---
 src/egl/drivers/dri2/platform_drm.c | 162 +++++++++++++++++++++++++----
 src/gbm/backends/dri/gbm_dri.c      | 202 +++++++++++++++++++++++++++++++-----
 src/gbm/backends/dri/gbm_driint.h   |  35 ++++++-
 src/gbm/main/gbm.h                  |   3 +
 4 files changed, 354 insertions(+), 48 deletions(-)

diff --git a/src/egl/drivers/dri2/platform_drm.c 
b/src/egl/drivers/dri2/platform_drm.c
index 6227bc9..6a0dcd3 100644
--- a/src/egl/drivers/dri2/platform_drm.c
+++ b/src/egl/drivers/dri2/platform_drm.c
@@ -44,6 +44,7 @@ lock_front_buffer(struct gbm_surface *_surf)
 {
    struct gbm_dri_surface *surf = (struct gbm_dri_surface *) _surf;
    struct dri2_egl_surface *dri2_surf = surf->dri_private;
+   struct gbm_dri_device *device = (struct gbm_dri_device *) _surf->gbm;
    struct gbm_bo *bo;
 
    if (dri2_surf->current == NULL) {
@@ -52,8 +53,11 @@ lock_front_buffer(struct gbm_surface *_surf)
    }
 
    bo = dri2_surf->current->bo;
-   dri2_surf->current->locked = 1;
-   dri2_surf->current = NULL;
+
+   if (device->dri2) {
+      dri2_surf->current->locked = 1;
+      dri2_surf->current = NULL;
+   }
 
    return bo;
 }
@@ -122,14 +126,27 @@ dri2_drm_create_surface(_EGLDriver *drv, _EGLDisplay 
*disp, EGLint type,
       goto cleanup_surf;
    }
 
-   dri2_surf->dri_drawable =
-      (*dri2_dpy->dri2->createNewDrawable) (dri2_dpy->dri_screen,
-                                           dri2_conf->dri_double_config,
-                                           dri2_surf->gbm_surf);
+   if (dri2_dpy->dri2) {
+      dri2_surf->dri_drawable =
+         (*dri2_dpy->dri2->createNewDrawable) (dri2_dpy->dri_screen,
+                                               dri2_conf->dri_double_config,
+                                               dri2_surf->gbm_surf);
 
-   if (dri2_surf->dri_drawable == NULL) {
-      _eglError(EGL_BAD_ALLOC, "dri2->createNewDrawable");
-      goto cleanup_surf;
+      if (dri2_surf->dri_drawable == NULL) {
+         _eglError(EGL_BAD_ALLOC, "dri2->createNewDrawable");
+         goto cleanup_surf;
+      }
+   } else {
+      assert (dri2_dpy->swrast != NULL);
+      dri2_surf->dri_drawable =
+         (*dri2_dpy->swrast->createNewDrawable) (dri2_dpy->dri_screen,
+                                                 dri2_conf->dri_double_config,
+                                                 dri2_surf->gbm_surf);
+
+      if (dri2_surf->dri_drawable == NULL) {
+         _eglError(EGL_BAD_ALLOC, "swrast->createNewDrawable");
+         goto cleanup_surf;
+      }
    }
 
    return &dri2_surf->base;
@@ -221,6 +238,28 @@ get_back_bo(struct dri2_egl_surface *dri2_surf)
    return 0;
 }
 
+static int
+get_swrast_front_bo(struct dri2_egl_surface *dri2_surf)
+{
+   struct dri2_egl_display *dri2_dpy =
+      dri2_egl_display(dri2_surf->base.Resource.Display);
+   struct gbm_dri_surface *surf = dri2_surf->gbm_surf;
+
+   if (dri2_surf->current == NULL) {
+      assert (!dri2_surf->color_buffers[0].locked);
+      dri2_surf->current = &dri2_surf->color_buffers[0];
+   }
+
+   if (dri2_surf->current->bo == NULL)
+      dri2_surf->current->bo = gbm_bo_create(&dri2_dpy->gbm_dri->base.base,
+                                             surf->base.width, 
surf->base.height,
+                                             surf->base.format, 
surf->base.flags);
+   if (dri2_surf->current->bo == NULL)
+      return -1;
+
+   return 0;
+}
+
 static void
 back_bo_to_dri_buffer(struct dri2_egl_surface *dri2_surf, __DRIbuffer *buffer)
 {
@@ -374,19 +413,23 @@ dri2_drm_swap_buffers(_EGLDriver *drv, _EGLDisplay *disp, 
_EGLSurface *draw)
    struct dri2_egl_surface *dri2_surf = dri2_egl_surface(draw);
    int i;
 
-   if (dri2_surf->base.Type == EGL_WINDOW_BIT) {
-      if (dri2_surf->current)
-        _eglError(EGL_BAD_SURFACE, "dri2_swap_buffers");
-      for (i = 0; i < ARRAY_SIZE(dri2_surf->color_buffers); i++)
-         if (dri2_surf->color_buffers[i].age > 0)
-            dri2_surf->color_buffers[i].age++;
-      dri2_surf->current = dri2_surf->back;
-      dri2_surf->current->age = 1;
-      dri2_surf->back = NULL;
-   }
+   if (dri2_dpy->swrast) {
+      (*dri2_dpy->core->swapBuffers)(dri2_surf->dri_drawable);
+   } else {
+      if (dri2_surf->base.Type == EGL_WINDOW_BIT) {
+         if (dri2_surf->current)
+            _eglError(EGL_BAD_SURFACE, "dri2_swap_buffers");
+         for (i = 0; i < ARRAY_SIZE(dri2_surf->color_buffers); i++)
+            if (dri2_surf->color_buffers[i].age > 0)
+               dri2_surf->color_buffers[i].age++;
+         dri2_surf->current = dri2_surf->back;
+         dri2_surf->current->age = 1;
+         dri2_surf->back = NULL;
+      }
 
-   (*dri2_dpy->flush->flush)(dri2_surf->dri_drawable);
-   (*dri2_dpy->flush->invalidate)(dri2_surf->dri_drawable);
+      (*dri2_dpy->flush->flush)(dri2_surf->dri_drawable);
+      (*dri2_dpy->flush->invalidate)(dri2_surf->dri_drawable);
+   }
 
    return EGL_TRUE;
 }
@@ -457,6 +500,74 @@ dri2_drm_authenticate(_EGLDisplay *disp, uint32_t id)
    return drmAuthMagic(dri2_dpy->fd, id);
 }
 
+static void
+swrast_put_image2(__DRIdrawable *driDrawable,
+                  int            op,
+                  int            x,
+                  int            y,
+                  int            width,
+                  int            height,
+                  int            stride,
+                  char          *data,
+                  void          *loaderPrivate)
+{
+   struct dri2_egl_surface *dri2_surf = loaderPrivate;
+   int internal_stride, i;
+   struct gbm_dri_bo *bo;
+
+   if (op != __DRI_SWRAST_IMAGE_OP_DRAW &&
+       op != __DRI_SWRAST_IMAGE_OP_SWAP)
+      return;
+
+   if (get_swrast_front_bo(dri2_surf) < 0)
+      return;
+   bo = gbm_dri_bo(dri2_surf->current->bo);
+   if (bo == NULL)
+      return;
+   if (gbm_dri_bo_map(bo) == NULL)
+      return;
+
+   internal_stride = bo->base.base.stride;
+
+   for (i = 0; i < height; i++) {
+      memcpy(bo->map + (x + i) * internal_stride + y,
+             data + i * stride, stride);
+   }
+
+   gbm_dri_bo_unmap(bo);
+}
+
+static void
+swrast_get_image(__DRIdrawable *driDrawable,
+                 int            x,
+                 int            y,
+                 int            width,
+                 int            height,
+                 char          *data,
+                 void          *loaderPrivate)
+{
+   struct dri2_egl_surface *dri2_surf = loaderPrivate;
+   int internal_stride, stride, i;
+   struct gbm_dri_bo *bo;
+
+   get_swrast_front_bo(dri2_surf);
+   bo = gbm_dri_bo(dri2_surf->current->bo);
+   if (bo == NULL)
+      return;
+   if (gbm_dri_bo_map(bo) == NULL)
+      return;
+
+   internal_stride = bo->base.base.stride;
+   stride = width * 4;
+
+   for (i = 0; i < height; i++) {
+      memcpy(data + i * stride,
+             bo->map + (x + i) * internal_stride + y, stride);
+   }
+
+   gbm_dri_bo_unmap(bo);
+}
+
 static struct dri2_egl_display_vtbl dri2_drm_display_vtbl = {
    .authenticate = dri2_drm_authenticate,
    .create_window_surface = dri2_drm_create_window_surface,
@@ -533,6 +644,7 @@ dri2_initialize_drm(_EGLDriver *drv, _EGLDisplay *disp)
    dri2_dpy->dri2 = dri2_dpy->gbm_dri->dri2;
    dri2_dpy->image = dri2_dpy->gbm_dri->image;
    dri2_dpy->flush = dri2_dpy->gbm_dri->flush;
+   dri2_dpy->swrast = dri2_dpy->gbm_dri->swrast;
    dri2_dpy->driver_configs = dri2_dpy->gbm_dri->driver_configs;
 
    dri2_dpy->gbm_dri->lookup_image = dri2_lookup_egl_image;
@@ -542,6 +654,8 @@ dri2_initialize_drm(_EGLDriver *drv, _EGLDisplay *disp)
    dri2_dpy->gbm_dri->flush_front_buffer = dri2_drm_flush_front_buffer;
    dri2_dpy->gbm_dri->get_buffers_with_format = 
dri2_drm_get_buffers_with_format;
    dri2_dpy->gbm_dri->image_get_buffers = dri2_drm_image_get_buffers;
+   dri2_dpy->gbm_dri->swrast_put_image2 = swrast_put_image2;
+   dri2_dpy->gbm_dri->swrast_get_image = swrast_get_image;
 
    dri2_dpy->gbm_dri->base.base.surface_lock_front_buffer = lock_front_buffer;
    dri2_dpy->gbm_dri->base.base.surface_release_buffer = release_buffer;
@@ -572,10 +686,12 @@ dri2_initialize_drm(_EGLDriver *drv, _EGLDisplay *disp)
                       i + 1, EGL_WINDOW_BIT, attr_list, NULL);
    }
 
-   disp->Extensions.EXT_buffer_age = EGL_TRUE;
+   if (dri2_dpy->dri2)
+      disp->Extensions.EXT_buffer_age = EGL_TRUE;
 
 #ifdef HAVE_WAYLAND_PLATFORM
-   disp->Extensions.WL_bind_wayland_display = EGL_TRUE;
+   if (dri2_dpy->image)
+      disp->Extensions.WL_bind_wayland_display = EGL_TRUE;
 #endif
 
    /* we're supporting EGL 1.4 */
diff --git a/src/gbm/backends/dri/gbm_dri.c b/src/gbm/backends/dri/gbm_dri.c
index 347bc99..8896a37 100644
--- a/src/gbm/backends/dri/gbm_dri.c
+++ b/src/gbm/backends/dri/gbm_dri.c
@@ -124,6 +124,74 @@ image_get_buffers(__DRIdrawable *driDrawable,
                                  surf->dri_private, buffer_mask, buffers);
 }
 
+static void
+swrast_get_drawable_info(__DRIdrawable *driDrawable,
+                         int           *x,
+                         int           *y,
+                         int           *width,
+                         int           *height,
+                         void          *loaderPrivate)
+{
+   struct gbm_dri_surface *surf = loaderPrivate;
+
+   *x = 0;
+   *y = 0;
+   *width = surf->base.width;
+   *height = surf->base.height;
+}
+
+static void
+swrast_put_image2(__DRIdrawable *driDrawable,
+                  int            op,
+                  int            x,
+                  int            y,
+                  int            width,
+                  int            height,
+                  int            stride,
+                  char          *data,
+                  void          *loaderPrivate)
+{
+   struct gbm_dri_surface *surf = loaderPrivate;
+   struct gbm_dri_device *dri = gbm_dri_device(surf->base.gbm);
+
+   dri->swrast_put_image2(driDrawable,
+                          op, x, y,
+                          width, height, stride,
+                          data, surf->dri_private);
+}
+
+static void
+swrast_put_image(__DRIdrawable *driDrawable,
+                 int            op,
+                 int            x,
+                 int            y,
+                 int            width,
+                 int            height,
+                 char          *data,
+                 void          *loaderPrivate)
+{
+   return swrast_put_image2(driDrawable, op, x, y, width, height,
+                            width * 4, data, loaderPrivate);
+}
+
+static void
+swrast_get_image(__DRIdrawable *driDrawable,
+                 int            x,
+                 int            y,
+                 int            width,
+                 int            height,
+                 char          *data,
+                 void          *loaderPrivate)
+{
+   struct gbm_dri_surface *surf = loaderPrivate;
+   struct gbm_dri_device *dri = gbm_dri_device(surf->base.gbm);
+
+   dri->swrast_get_image(driDrawable,
+                         x, y,
+                         width, height,
+                         data, surf->dri_private);
+}
+
 static const __DRIuseInvalidateExtension use_invalidate = {
    .base = { __DRI_USE_INVALIDATE, 1 }
 };
@@ -149,11 +217,21 @@ static const __DRIimageLoaderExtension 
image_loader_extension = {
    .flushFrontBuffer    = dri_flush_front_buffer,
 };
 
+static const __DRIswrastLoaderExtension swrast_loader_extension = {
+   .base = { __DRI_SWRAST_LOADER, 2 },
+
+   .getDrawableInfo = swrast_get_drawable_info,
+   .putImage        = swrast_put_image,
+   .getImage        = swrast_get_image,
+   .putImage2       = swrast_put_image2
+};
+
 static const __DRIextension *gbm_dri_screen_extensions[] = {
    &image_lookup_extension.base,
    &use_invalidate.base,
    &dri2_loader_extension.base,
    &image_loader_extension.base,
+   &swrast_loader_extension.base,
    NULL,
 };
 
@@ -175,6 +253,12 @@ static struct dri_extension_match 
gbm_dri_device_extensions[] = {
    { NULL, 0, 0 }
 };
 
+static struct dri_extension_match gbm_swrast_device_extensions[] = {
+   { __DRI_CORE, 1, offsetof(struct gbm_dri_device, core), },
+   { __DRI_SWRAST, 1, offsetof(struct gbm_dri_device, swrast) },
+   { NULL, 0, 0 }
+};
+
 static int
 dri_bind_extensions(struct gbm_dri_device *dri,
                     struct dri_extension_match *matches,
@@ -269,9 +353,11 @@ dri_load_driver(struct gbm_dri_device *dri)
    dri->driver_extensions = extensions;
 
    if (dri_bind_extensions(dri, gbm_dri_device_extensions, extensions) < 0) {
-      dlclose(dri->driver);
-      fprintf(stderr, "failed to bind extensions\n");
-      return -1;
+      if (dri_bind_extensions(dri, gbm_swrast_device_extensions, extensions) < 
0) {
+         dlclose(dri->driver);
+         fprintf(stderr, "failed to bind extensions\n");
+         return -1;
+      }
    }
 
    return 0;
@@ -329,6 +415,39 @@ free_screen:
 }
 
 static int
+dri_screen_create_swrast(struct gbm_dri_device *dri)
+{
+   int ret = 0;
+
+   dri->base.driver_name = "swrast";
+
+   ret = dri_load_driver(dri);
+   if (ret) {
+      fprintf(stderr, "failed to load swrast driver\n");
+      return ret;
+   }
+
+   dri->extensions = gbm_dri_screen_extensions;
+
+   if (dri->swrast == NULL)
+      return -1;
+
+   if (dri->swrast->base.version >= 4) {
+      dri->screen = dri->swrast->createNewScreen2(0, dri->extensions,
+                                                  dri->driver_extensions,
+                                                  &dri->driver_configs, dri);
+   } else {
+      dri->screen = dri->swrast->createNewScreen(0, dri->extensions,
+                                                 &dri->driver_configs, dri);
+   }
+
+   dri->lookup_image = NULL;
+   dri->lookup_user_data = NULL;
+
+   return 0;
+}
+
+static int
 gbm_dri_is_format_supported(struct gbm_device *gbm,
                             uint32_t format,
                             uint32_t usage)
@@ -393,7 +512,7 @@ gbm_dri_bo_destroy(struct gbm_bo *_bo)
    if (bo->image != NULL) {
       dri->image->destroyImage(bo->image);
    } else {
-      munmap(bo->map, bo->size);
+      gbm_dri_bo_unmap(bo);
       memset(&arg, 0, sizeof(arg));
       arg.handle = bo->handle;
       drmIoctl(dri->base.base.fd, DRM_IOCTL_MODE_DESTROY_DUMB, &arg);
@@ -439,7 +558,7 @@ gbm_dri_bo_import(struct gbm_device *gbm,
    int gbm_format;
 
    /* Required for query image WIDTH & HEIGHT */
-   if (dri->image->base.version < 4) {
+   if (dri->image == NULL || dri->image->base.version < 4) {
       errno = ENOSYS;
       return NULL;
    }
@@ -563,16 +682,16 @@ create_dumb(struct gbm_device *gbm,
 {
    struct gbm_dri_device *dri = gbm_dri_device(gbm);
    struct drm_mode_create_dumb create_arg;
-   struct drm_mode_map_dumb map_arg;
    struct gbm_dri_bo *bo;
    struct drm_mode_destroy_dumb destroy_arg;
    int ret;
+   int is_cursor, is_scanout;
 
-   if (!(usage & GBM_BO_USE_CURSOR)) {
-      errno = EINVAL;
-      return NULL;
-   }
-   if (format != GBM_FORMAT_ARGB8888) {
+   is_cursor = (usage & GBM_BO_USE_CURSOR) != 0 &&
+      format == GBM_FORMAT_ARGB8888;
+   is_scanout = (usage & GBM_BO_USE_SCANOUT) != 0 &&
+      format == GBM_FORMAT_XRGB8888;
+   if (!is_cursor && !is_scanout) {
       errno = EINVAL;
       return NULL;
    }
@@ -598,16 +717,7 @@ create_dumb(struct gbm_device *gbm,
    bo->handle = create_arg.handle;
    bo->size = create_arg.size;
 
-   memset(&map_arg, 0, sizeof(map_arg));
-   map_arg.handle = bo->handle;
-
-   ret = drmIoctl(dri->base.base.fd, DRM_IOCTL_MODE_MAP_DUMB, &map_arg);
-   if (ret)
-      goto destroy_dumb;
-
-   bo->map = mmap(0, bo->size, PROT_WRITE,
-                  MAP_SHARED, dri->base.base.fd, map_arg.offset);
-   if (bo->map == MAP_FAILED)
+   if (gbm_dri_bo_map(bo) == NULL)
       goto destroy_dumb;
 
    return &bo->base.base;
@@ -622,6 +732,40 @@ free_bo:
    return NULL;
 }
 
+static void *
+gbm_dri_real_bo_map(struct gbm_dri_bo *bo)
+{
+   struct drm_mode_map_dumb map_arg;
+   int ret;
+
+   if (bo->image != NULL)
+      return NULL;
+
+   if (bo->map != NULL)
+      return bo->map;
+
+   memset(&map_arg, 0, sizeof(map_arg));
+   map_arg.handle = bo->handle;
+
+   ret = drmIoctl(bo->base.base.gbm->fd, DRM_IOCTL_MODE_MAP_DUMB, &map_arg);
+   if (ret)
+      return NULL;
+
+   bo->map = mmap(0, bo->size, PROT_WRITE,
+                  MAP_SHARED, bo->base.base.gbm->fd, map_arg.offset);
+   if (bo->map == MAP_FAILED)
+      return NULL;
+
+   return bo->map;
+}
+
+static void
+gbm_dri_real_bo_unmap(struct gbm_dri_bo *bo)
+{
+   munmap(bo->map, bo->size);
+   bo->map = NULL;
+}
+
 static struct gbm_bo *
 gbm_dri_bo_create(struct gbm_device *gbm,
                   uint32_t width, uint32_t height,
@@ -632,7 +776,7 @@ gbm_dri_bo_create(struct gbm_device *gbm,
    int dri_format;
    unsigned dri_use = 0;
 
-   if (usage & GBM_BO_USE_WRITE)
+   if (usage & GBM_BO_USE_WRITE || dri->image == NULL)
       return create_dumb(gbm, width, height, format, usage);
 
    bo = calloc(1, sizeof *bo);
@@ -743,7 +887,7 @@ static struct gbm_device *
 dri_device_create(int fd)
 {
    struct gbm_dri_device *dri;
-   int ret;
+   int ret, force_sw;
 
    dri = calloc(1, sizeof *dri);
    if (!dri)
@@ -756,6 +900,8 @@ dri_device_create(int fd)
    dri->base.base.bo_write = gbm_dri_bo_write;
    dri->base.base.bo_get_fd = gbm_dri_bo_get_fd;
    dri->base.base.bo_destroy = gbm_dri_bo_destroy;
+   dri->bo_map = gbm_dri_real_bo_map;
+   dri->bo_unmap = gbm_dri_real_bo_unmap;
    dri->base.base.destroy = dri_destroy;
    dri->base.base.surface_create = gbm_dri_surface_create;
    dri->base.base.surface_destroy = gbm_dri_surface_destroy;
@@ -763,7 +909,15 @@ dri_device_create(int fd)
    dri->base.type = GBM_DRM_DRIVER_TYPE_DRI;
    dri->base.base.name = "drm";
 
-   ret = dri_screen_create(dri);
+   force_sw = getenv("LIBGL_ALWAYS_SOFTWARE") != NULL;
+   if (!force_sw) {
+      ret = dri_screen_create(dri);
+      if (!ret)
+         ret = dri_screen_create_swrast(dri);
+   } else {
+      ret = dri_screen_create_swrast(dri);
+   }
+
    if (ret)
       goto err_dri;
 
diff --git a/src/gbm/backends/dri/gbm_driint.h 
b/src/gbm/backends/dri/gbm_driint.h
index 9c4392d..b163ad6 100644
--- a/src/gbm/backends/dri/gbm_driint.h
+++ b/src/gbm/backends/dri/gbm_driint.h
@@ -36,6 +36,7 @@
 #include "GL/internal/dri_interface.h"
 
 struct gbm_dri_surface;
+struct gbm_dri_bo;
 
 struct gbm_dri_device {
    struct gbm_drm_device base;
@@ -47,6 +48,7 @@ struct gbm_dri_device {
    const __DRIcoreExtension   *core;
    const __DRIdri2Extension   *dri2;
    const __DRIimageExtension  *image;
+   const __DRIswrastExtension *swrast;
    const __DRI2flushExtension *flush;
    const __DRIdri2LoaderExtension *loader;
 
@@ -54,6 +56,9 @@ struct gbm_dri_device {
    const __DRIextension **extensions;
    const __DRIextension **driver_extensions;
 
+   void *(*bo_map)   (struct gbm_dri_bo *bo);
+   void  (*bo_unmap) (struct gbm_dri_bo *bo);
+
    __DRIimage *(*lookup_image)(__DRIscreen *screen, void *image, void *data);
    void *lookup_user_data;
 
@@ -72,6 +77,22 @@ struct gbm_dri_device {
                             void *loaderPrivate,
                             uint32_t buffer_mask,
                             struct __DRIimageList *buffers);
+   void (*swrast_put_image2)(__DRIdrawable *driDrawable,
+                             int            op,
+                             int            x,
+                             int            y,
+                             int            width,
+                             int            height,
+                             int            stride,
+                             char          *data,
+                             void          *loaderPrivate);
+   void (*swrast_get_image)(__DRIdrawable *driDrawable,
+                            int            x,
+                            int            y,
+                            int            width,
+                            int            height,
+                            char          *data,
+                            void          *loaderPrivate);
 
    struct wl_drm *wl_drm;
 };
@@ -81,7 +102,7 @@ struct gbm_dri_bo {
 
    __DRIimage *image;
 
-   /* Only used for cursors */
+   /* Used for cursors and the swrast front BO */
    uint32_t handle, size;
    void *map;
 };
@@ -110,4 +131,16 @@ gbm_dri_surface(struct gbm_surface *surface)
    return (struct gbm_dri_surface *) surface;
 }
 
+static inline void *
+gbm_dri_bo_map(struct gbm_dri_bo *bo)
+{
+   return gbm_dri_device(bo->base.base.gbm)->bo_map(bo);
+}
+
+static inline void
+gbm_dri_bo_unmap(struct gbm_dri_bo *bo)
+{
+   return gbm_dri_device(bo->base.base.gbm)->bo_unmap(bo);
+}
+
 #endif
diff --git a/src/gbm/main/gbm.h b/src/gbm/main/gbm.h
index 374cef8..7b23c26 100644
--- a/src/gbm/main/gbm.h
+++ b/src/gbm/main/gbm.h
@@ -287,6 +287,9 @@ gbm_surface_create(struct gbm_device *gbm,
                    uint32_t width, uint32_t height,
                   uint32_t format, uint32_t flags);
 
+int
+gbm_surface_needs_lock_front_buffer(struct gbm_surface *surface);
+
 struct gbm_bo *
 gbm_surface_lock_front_buffer(struct gbm_surface *surface);
 
-- 
1.9.3

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