GBM device

struct gbm_device {
   /* Hack to make a gbm_device detectable by its first element. */
   struct gbm_device *(*dummy)(int);

   int fd;
   const char *name;
   unsigned int refcount;
   struct stat stat;

   void (*destroy)(struct gbm_device *gbm);
   int (*is_format_supported)(struct gbm_device *gbm,
                              uint32_t format,
                              uint32_t usage);
   int (*get_format_modifier_plane_count)(struct gbm_device *device,
                                          uint32_t format,
                                          uint64_t modifier);

   struct gbm_bo *(*bo_create)(struct gbm_device *gbm,
                               uint32_t width, uint32_t height,
                               uint32_t format,
                               uint32_t usage,
                               const uint64_t *modifiers,
                               const unsigned int count);
   struct gbm_bo *(*bo_import)(struct gbm_device *gbm, uint32_t type,
                               void *buffer, uint32_t usage);
   void *(*bo_map)(struct gbm_bo *bo,
                               uint32_t x, uint32_t y,
                               uint32_t width, uint32_t height,
                               uint32_t flags, uint32_t *stride,
                               void **map_data);
   void (*bo_unmap)(struct gbm_bo *bo, void *map_data);
   int (*bo_write)(struct gbm_bo *bo, const void *buf, size_t data);
   int (*bo_get_fd)(struct gbm_bo *bo);
   int (*bo_get_planes)(struct gbm_bo *bo);
   union gbm_bo_handle (*bo_get_handle)(struct gbm_bo *bo, int plane);
   uint32_t (*bo_get_stride)(struct gbm_bo *bo, int plane);
   uint32_t (*bo_get_offset)(struct gbm_bo *bo, int plane);
   uint64_t (*bo_get_modifier)(struct gbm_bo *bo);
   void (*bo_destroy)(struct gbm_bo *bo);

   struct gbm_surface *(*surface_create)(struct gbm_device *gbm,
                                         uint32_t width, uint32_t height,
                                         uint32_t format, uint32_t flags,
                                         const uint64_t *modifiers,
                                         const unsigned count);
   struct gbm_bo *(*surface_lock_front_buffer)(struct gbm_surface *surface);
   void (*surface_release_buffer)(struct gbm_surface *surface,
                                  struct gbm_bo *bo);
   int (*surface_has_free_buffers)(struct gbm_surface *surface);
   void (*surface_destroy)(struct gbm_surface *surface);
};

GBM surface

struct gbm_surface {
   struct gbm_device *gbm;
   uint32_t width;
   uint32_t height;
   uint32_t format;
   uint32_t flags;
   struct {
      uint64_t *modifiers;
      unsigned count;
   };
};

/**
 * Return whether or not a surface has free (non-locked) buffers
 *
 * Before starting a new frame, the surface must have a buffer
 * available for rendering.  Initially, a gbm surface will have a free
 * buffer, but after one or more buffers have been locked (\sa
 * gbm_surface_lock_front_buffer()), the application must check for a
 * free buffer before rendering.
 *
 * If a surface doesn't have a free buffer, the application must
 * return a buffer to the surface using gbm_surface_release_buffer()
 * and after that, the application can query for free buffers again.
 *
 * \param surf The surface
 * \return 1 if the surface has free buffers, 0 otherwise
 */
GBM_EXPORT int
gbm_surface_has_free_buffers(struct gbm_surface *surf)
{
   return surf->gbm->surface_has_free_buffers(surf);
}