src/gbm/main/gbm.c

   1 /*
   2  * Copyright © 2011 Intel Corporation
   3  *
   4  * Permission is hereby granted, free of charge, to any person obtaining a
   5  * copy of this software and associated documentation files (the "Software"),
   6  * to deal in the Software without restriction, including without limitation
   7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
   8  * and/or sell copies of the Software, and to permit persons to whom the
   9  * Software is furnished to do so, subject to the following conditions:
  10  *
  11  * The above copyright notice and this permission notice (including the next
  12  * paragraph) shall be included in all copies or substantial portions of the
  13  * Software.
  14  *
  15  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
  16  * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
  17  * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
  18  * NONINFRINGEMENT.  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
  19  * HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
  20  * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
  22  * DEALINGS IN THE SOFTWARE.
  23  *
  24  * Authors:
  25  *    Benjamin Franzke <benjaminfranzke@googlemail.com>
  26  */
  27
  28 #include <stddef.h>
  29 #include <stdio.h>
  30 #include <stdlib.h>
  31 #include <string.h>
  32 #include <stdint.h>
  33
  34 #ifdef MAJOR_IN_MKDEV
  35 #include <sys/mkdev.h>
  36 #endif
  37 #ifdef MAJOR_IN_SYSMACROS
  38 #include <sys/sysmacros.h>
  39 #endif
  40 #include <sys/stat.h>
  41 #include <unistd.h>
  42 #include <errno.h>
  43
  44 #include "gbm.h"
  45 #include "gbmint.h"
  46 #include "backend.h"
  47
  48 /** Returns the file description for the gbm device
  49  *
  50  * \return The fd that the struct gbm_device was created with
  51  */
  52 GBM_EXPORT int
  53 gbm_device_get_fd(struct gbm_device *gbm)
  54 {
  55    return gbm->fd;
  56 }
  57
  58 /** Get the backend name for the given gbm device
  59  *
  60  * \return The backend name string - this belongs to the device and must not
  61  * be freed
  62  */
  63 GBM_EXPORT const char *
  64 gbm_device_get_backend_name(struct gbm_device *gbm)
  65 {
  66    return gbm->name;
  67 }
  68
  69 /** Test if a format is supported for a given set of usage flags.
  70  *
  71  * \param gbm The created buffer manager
  72  * \param format The format to test
  73  * \param usage A bitmask of the usages to test the format against
  74  * \return 1 if the format is supported otherwise 0
  75  *
  76  * \sa enum gbm_bo_flags for the list of flags that the format can be
  77  * tested against
  78  *
  79  * \sa enum gbm_bo_format for the list of formats
  80  */
  81 GBM_EXPORT int
  82 gbm_device_is_format_supported(struct gbm_device *gbm,
  83                                uint32_t format, uint32_t usage)
  84 {
  85    return gbm->is_format_supported(gbm, format, usage);
  86 }
  87
  88 /** Destroy the gbm device and free all resources associated with it.
  89  *
  90  * \param gbm The device created using gbm_create_device()
  91  */
  92 GBM_EXPORT void
  93 gbm_device_destroy(struct gbm_device *gbm)
  94 {
  95    gbm->refcount--;
  96    if (gbm->refcount == 0)
  97       gbm->destroy(gbm);
  98 }
  99
 100 /** Create a gbm device for allocating buffers
 101  *
 102  * The file descriptor passed in is used by the backend to communicate with
 103  * platform for allocating the memory. For allocations using DRI this would be
 104  * the file descriptor returned when opening a device such as \c
 105  * /dev/dri/card0
 106  *
 107  * \param fd The file descriptor for a backend specific device
 108  * \return The newly created struct gbm_device. The resources associated with
 109  * the device should be freed with gbm_device_destroy() when it is no longer
 110  * needed. If the creation of the device failed NULL will be returned.
 111  */
 112 GBM_EXPORT struct gbm_device *
 113 gbm_create_device(int fd)
 114 {
 115    struct gbm_device *gbm = NULL;
 116    struct stat buf;
 117
 118    if (fd < 0 || fstat(fd, &buf) < 0 || !S_ISCHR(buf.st_mode)) {
 119       errno = EINVAL;
 120       return NULL;
 121    }
 122
 123    gbm = _gbm_create_device(fd);
 124    if (gbm == NULL)
 125       return NULL;
 126
 127    gbm->dummy = gbm_create_device;
 128    gbm->stat = buf;
 129    gbm->refcount = 1;
 130
 131    return gbm;
 132 }
 133
 134 /** Get the width of the buffer object
 135  *
 136  * \param bo The buffer object
 137  * \return The width of the allocated buffer object
 138  *
 139  */
 140 GBM_EXPORT uint32_t
 141 gbm_bo_get_width(struct gbm_bo *bo)
 142 {
 143    return bo->width;
 144 }
 145
 146 /** Get the height of the buffer object
 147  *
 148  * \param bo The buffer object
 149  * \return The height of the allocated buffer object
 150  */
 151 GBM_EXPORT uint32_t
 152 gbm_bo_get_height(struct gbm_bo *bo)
 153 {
 154    return bo->height;
 155 }
 156
 157 /** Get the stride of the buffer object
 158  *
 159  * This is calculated by the backend when it does the allocation in
 160  * gbm_bo_create()
 161  *
 162  * \param bo The buffer object
 163  * \return The stride of the allocated buffer object in bytes
 164  */
 165 GBM_EXPORT uint32_t
 166 gbm_bo_get_stride(struct gbm_bo *bo)
 167 {
 168    return gbm_bo_get_stride_for_plane(bo, 0);
 169 }
 170
 171 /** Get the stride for the given plane
 172  *
 173  * \param bo The buffer object
 174  * \param plane for which you want the stride
 175  *
 176  * \sa gbm_bo_get_stride()
 177  */
 178 GBM_EXPORT uint32_t
 179 gbm_bo_get_stride_for_plane(struct gbm_bo *bo, int plane)
 180 {
 181    return bo->gbm->bo_get_stride(bo, plane);
 182 }
 183
 184 /** Get the format of the buffer object
 185  *
 186  * The format of the pixels in the buffer.
 187  *
 188  * \param bo The buffer object
 189  * \return The format of buffer object, one of the GBM_FORMAT_* codes
 190  */
 191 GBM_EXPORT uint32_t
 192 gbm_bo_get_format(struct gbm_bo *bo)
 193 {
 194    return bo->format;
 195 }
 196
 197 /** Get the bit-per-pixel of the buffer object's format
 198  *
 199  * The bits-per-pixel of the buffer object's format.
 200  *
 201  * Note; The 'in-memory pixel' concept makes no sense for YUV formats
 202  * (pixels are the result of the combination of multiple memory sources:
 203  * Y, Cb & Cr; usually these are even in separate buffers), so YUV
 204  * formats are not supported by this function.
 205  *
 206  * \param bo The buffer object
 207  * \return The number of bits0per-pixel of the buffer object's format.
 208  */
 209 GBM_EXPORT uint32_t
 210 gbm_bo_get_bpp(struct gbm_bo *bo)
 211 {
 212    switch (bo->format) {
 213       default:
 214          return 0;
 215       case GBM_FORMAT_C8:
 216       case GBM_FORMAT_R8:
 217       case GBM_FORMAT_RGB332:
 218       case GBM_FORMAT_BGR233:
 219          return 8;
 220       case GBM_FORMAT_GR88:
 221       case GBM_FORMAT_XRGB4444:
 222       case GBM_FORMAT_XBGR4444:
 223       case GBM_FORMAT_RGBX4444:
 224       case GBM_FORMAT_BGRX4444:
 225       case GBM_FORMAT_ARGB4444:
 226       case GBM_FORMAT_ABGR4444:
 227       case GBM_FORMAT_RGBA4444:
 228       case GBM_FORMAT_BGRA4444:
 229       case GBM_FORMAT_XRGB1555:
 230       case GBM_FORMAT_XBGR1555:
 231       case GBM_FORMAT_RGBX5551:
 232       case GBM_FORMAT_BGRX5551:
 233       case GBM_FORMAT_ARGB1555:
 234       case GBM_FORMAT_ABGR1555:
 235       case GBM_FORMAT_RGBA5551:
 236       case GBM_FORMAT_BGRA5551:
 237       case GBM_FORMAT_RGB565:
 238       case GBM_FORMAT_BGR565:
 239          return 16;
 240       case GBM_FORMAT_RGB888:
 241       case GBM_FORMAT_BGR888:
 242          return 24;
 243       case GBM_FORMAT_XRGB8888:
 244       case GBM_FORMAT_XBGR8888:
 245       case GBM_FORMAT_RGBX8888:
 246       case GBM_FORMAT_BGRX8888:
 247       case GBM_FORMAT_ARGB8888:
 248       case GBM_FORMAT_ABGR8888:
 249       case GBM_FORMAT_RGBA8888:
 250       case GBM_FORMAT_BGRA8888:
 251       case GBM_FORMAT_XRGB2101010:
 252       case GBM_FORMAT_XBGR2101010:
 253       case GBM_FORMAT_RGBX1010102:
 254       case GBM_FORMAT_BGRX1010102:
 255       case GBM_FORMAT_ARGB2101010:
 256       case GBM_FORMAT_ABGR2101010:
 257       case GBM_FORMAT_RGBA1010102:
 258       case GBM_FORMAT_BGRA1010102:
 259          return 32;
 260    }
 261 }
 262
 263 /** Get the offset for the data of the specified plane
 264  *
 265  * Extra planes, and even the first plane, may have an offset from the start of
 266  * the buffer object. This function will provide the offset for the given plane
 267  * to be used in various KMS APIs.
 268  *
 269  * \param bo The buffer object
 270  * \return The offset
 271  */
 272 GBM_EXPORT uint32_t
 273 gbm_bo_get_offset(struct gbm_bo *bo, int plane)
 274 {
 275    return bo->gbm->bo_get_offset(bo, plane);
 276 }
 277
 278 /** Get the gbm device used to create the buffer object
 279  *
 280  * \param bo The buffer object
 281  * \return Returns the gbm device with which the buffer object was created
 282  */
 283 GBM_EXPORT struct gbm_device *
 284 gbm_bo_get_device(struct gbm_bo *bo)
 285 {
 286         return bo->gbm;
 287 }
 288
 289 /** Get the handle of the buffer object
 290  *
 291  * This is stored in the platform generic union gbm_bo_handle type. However
 292  * the format of this handle is platform specific.
 293  *
 294  * \param bo The buffer object
 295  * \return Returns the handle of the allocated buffer object
 296  */
 297 GBM_EXPORT union gbm_bo_handle
 298 gbm_bo_get_handle(struct gbm_bo *bo)
 299 {
 300    return bo->handle;
 301 }
 302
 303 /** Get a DMA-BUF file descriptor for the buffer object
 304  *
 305  * This function creates a DMA-BUF (also known as PRIME) file descriptor
 306  * handle for the buffer object.  Each call to gbm_bo_get_fd() returns a new
 307  * file descriptor and the caller is responsible for closing the file
 308  * descriptor.
 309
 310  * \param bo The buffer object
 311  * \return Returns a file descriptor referring to the underlying buffer or -1
 312  * if an error occurs.
 313  */
 314 GBM_EXPORT int
 315 gbm_bo_get_fd(struct gbm_bo *bo)
 316 {
 317    return bo->gbm->bo_get_fd(bo);
 318 }
 319
 320 /** Get the number of planes for the given bo.
 321  *
 322  * \param bo The buffer object
 323  * \return The number of planes
 324  */
 325 GBM_EXPORT int
 326 gbm_bo_get_plane_count(struct gbm_bo *bo)
 327 {
 328    return bo->gbm->bo_get_planes(bo);
 329 }
 330
 331 /** Get the handle for the specified plane of the buffer object
 332  *
 333  * This function gets the handle for any plane associated with the BO. When
 334  * dealing with multi-planar formats, or formats which might have implicit
 335  * planes based on different underlying hardware it is necessary for the client
 336  * to be able to get this information to pass to the DRM.
 337  *
 338  * \param bo The buffer object
 339  * \param plane the plane to get a handle for
 340  *
 341  * \sa gbm_bo_get_handle()
 342  */
 343 GBM_EXPORT union gbm_bo_handle
 344 gbm_bo_get_handle_for_plane(struct gbm_bo *bo, int plane)
 345 {
 346    return bo->gbm->bo_get_handle(bo, plane);
 347 }
 348
 349 /**
 350  * Get the chosen modifier for the buffer object
 351  *
 352  * This function returns the modifier that was chosen for the object. These
 353  * properties may be generic, or platform/implementation dependent.
 354  *
 355  * \param bo The buffer object
 356  * \return Returns the selected modifier (chosen by the implementation) for the
 357  * BO.
 358  * \sa gbm_bo_create_with_modifiers() where possible modifiers are set
 359  * \sa gbm_surface_create_with_modifiers() where possible modifiers are set
 360  * \sa define DRM_FORMAT_MOD_* in drm_fourcc.h for possible modifiers
 361  */
 362 GBM_EXPORT uint64_t
 363 gbm_bo_get_modifier(struct gbm_bo *bo)
 364 {
 365    return bo->gbm->bo_get_modifier(bo);
 366 }
 367
 368 /** Write data into the buffer object
 369  *
 370  * If the buffer object was created with the GBM_BO_USE_WRITE flag,
 371  * this function can be used to write data into the buffer object.  The
 372  * data is copied directly into the object and it's the responsibility
 373  * of the caller to make sure the data represents valid pixel data,
 374  * according to the width, height, stride and format of the buffer object.
 375  *
 376  * \param bo The buffer object
 377  * \param buf The data to write
 378  * \param count The number of bytes to write
 379  * \return Returns 0 on success, otherwise -1 is returned an errno set
 380  */
 381 GBM_EXPORT int
 382 gbm_bo_write(struct gbm_bo *bo, const void *buf, size_t count)
 383 {
 384    return bo->gbm->bo_write(bo, buf, count);
 385 }
 386
 387 /** Set the user data associated with a buffer object
 388  *
 389  * \param bo The buffer object
 390  * \param data The data to associate to the buffer object
 391  * \param destroy_user_data A callback (which may be %NULL) that will be
 392  * called prior to the buffer destruction
 393  */
 394 GBM_EXPORT void
 395 gbm_bo_set_user_data(struct gbm_bo *bo, void *data,
 396                      void (*destroy_user_data)(struct gbm_bo *, void *))
 397 {
 398    bo->user_data = data;
 399    bo->destroy_user_data = destroy_user_data;
 400 }
 401
 402 /** Get the user data associated with a buffer object
 403  *
 404  * \param bo The buffer object
 405  * \return Returns the user data associated with the buffer object or %NULL
 406  * if no data was associated with it
 407  *
 408  * \sa gbm_bo_set_user_data()
 409  */
 410 GBM_EXPORT void *
 411 gbm_bo_get_user_data(struct gbm_bo *bo)
 412 {
 413    return bo->user_data;
 414 }
 415
 416 /**
 417  * Destroys the given buffer object and frees all resources associated with
 418  * it.
 419  *
 420  * \param bo The buffer object
 421  */
 422 GBM_EXPORT void
 423 gbm_bo_destroy(struct gbm_bo *bo)
 424 {
 425    if (bo->destroy_user_data)
 426       bo->destroy_user_data(bo, bo->user_data);
 427
 428    bo->gbm->bo_destroy(bo);
 429 }
 430
 431 /**
 432  * Allocate a buffer object for the given dimensions
 433  *
 434  * \param gbm The gbm device returned from gbm_create_device()
 435  * \param width The width for the buffer
 436  * \param height The height for the buffer
 437  * \param format The format to use for the buffer
 438  * \param usage The union of the usage flags for this buffer
 439  *
 440  * \return A newly allocated buffer that should be freed with gbm_bo_destroy()
 441  * when no longer needed. If an error occurs during allocation %NULL will be
 442  * returned and errno set.
 443  *
 444  * \sa enum gbm_bo_format for the list of formats
 445  * \sa enum gbm_bo_flags for the list of usage flags
 446  */
 447 GBM_EXPORT struct gbm_bo *
 448 gbm_bo_create(struct gbm_device *gbm,
 449               uint32_t width, uint32_t height,
 450               uint32_t format, uint32_t usage)
 451 {
 452    if (width == 0 || height == 0) {
 453       errno = EINVAL;
 454       return NULL;
 455    }
 456
 457    return gbm->bo_create(gbm, width, height, format, usage, NULL, 0);
 458 }
 459
 460 GBM_EXPORT struct gbm_bo *
 461 gbm_bo_create_with_modifiers(struct gbm_device *gbm,
 462                              uint32_t width, uint32_t height,
 463                              uint32_t format,
 464                              const uint64_t *modifiers,
 465                              const unsigned int count)
 466 {
 467    if (width == 0 || height == 0) {
 468       errno = EINVAL;
 469       return NULL;
 470    }
 471
 472    if ((count && !modifiers) || (modifiers && !count)) {
 473       errno = EINVAL;
 474       return NULL;
 475    }
 476
 477    return gbm->bo_create(gbm, width, height, format, 0, modifiers, count);
 478 }
 479 /**
 480  * Create a gbm buffer object from an foreign object
 481  *
 482  * This function imports a foreign object and creates a new gbm bo for it.
 483  * This enabled using the foreign object with a display API such as KMS.
 484  * Currently three types of foreign objects are supported, indicated by the type
 485  * argument:
 486  *
 487  *   GBM_BO_IMPORT_WL_BUFFER
 488  *   GBM_BO_IMPORT_EGL_IMAGE
 489  *   GBM_BO_IMPORT_FD
 490  *
 491  * The gbm bo shares the underlying pixels but its life-time is
 492  * independent of the foreign object.
 493  *
 494  * \param gbm The gbm device returned from gbm_create_device()
 495  * \param type The type of object we're importing
 496  * \param buffer Pointer to the external object
 497  * \param usage The union of the usage flags for this buffer
 498  *
 499  * \return A newly allocated buffer object that should be freed with
 500  * gbm_bo_destroy() when no longer needed. On error, %NULL is returned
 501  * and errno is set.
 502  *
 503  * \sa enum gbm_bo_flags for the list of usage flags
 504  */
 505 GBM_EXPORT struct gbm_bo *
 506 gbm_bo_import(struct gbm_device *gbm,
 507               uint32_t type, void *buffer, uint32_t usage)
 508 {
 509    return gbm->bo_import(gbm, type, buffer, usage);
 510 }
 511
 512 /**
 513  * Map a region of a gbm buffer object for cpu access
 514  *
 515  * This function maps a region of a gbm bo for cpu read and/or write
 516  * access.
 517  *
 518  * \param bo The buffer object
 519  * \param x The X (top left origin) starting position of the mapped region for
 520  * the buffer
 521  * \param y The Y (top left origin) starting position of the mapped region for
 522  * the buffer
 523  * \param width The width of the mapped region for the buffer
 524  * \param height The height of the mapped region for the buffer
 525  * \param flags The union of the GBM_BO_TRANSFER_* flags for this buffer
 526  * \param stride Ptr for returned stride in bytes of the mapped region
 527  * \param map_data Returned opaque ptr for the mapped region
 528  *
 529  * \return Address of the mapped buffer that should be unmapped with
 530  * gbm_bo_unmap() when no longer needed. On error, %NULL is returned
 531  * and errno is set.
 532  *
 533  * \sa enum gbm_bo_transfer_flags for the list of flags
 534  */
 535 GBM_EXPORT void *
 536 gbm_bo_map(struct gbm_bo *bo,
 537               uint32_t x, uint32_t y,
 538               uint32_t width, uint32_t height,
 539               uint32_t flags, uint32_t *stride, void **map_data)
 540 {
 541    if (!bo || width == 0 || height == 0 || !stride || !map_data) {
 542       errno = EINVAL;
 543       return NULL;
 544    }
 545
 546    return bo->gbm->bo_map(bo, x, y, width, height,
 547                           flags, stride, map_data);
 548 }
 549
 550 /**
 551  * Unmap a previously mapped region of a gbm buffer object
 552  *
 553  * This function unmaps a region of a gbm bo for cpu read and/or write
 554  * access.
 555  *
 556  * \param bo The buffer object
 557  * \param map_data opaque ptr returned from prior gbm_bo_map
 558  */
 559 GBM_EXPORT void
 560 gbm_bo_unmap(struct gbm_bo *bo, void *map_data)
 561 {
 562    bo->gbm->bo_unmap(bo, map_data);
 563 }
 564
 565 /**
 566  * Allocate a surface object
 567  *
 568  * \param gbm The gbm device returned from gbm_create_device()
 569  * \param width The width for the surface
 570  * \param height The height for the surface
 571  * \param format The format to use for the surface
 572  *
 573  * \return A newly allocated surface that should be freed with
 574  * gbm_surface_destroy() when no longer needed. If an error occurs
 575  * during allocation %NULL will be returned.
 576  *
 577  * \sa enum gbm_bo_format for the list of formats
 578  */
 579 GBM_EXPORT struct gbm_surface *
 580 gbm_surface_create(struct gbm_device *gbm,
 581                    uint32_t width, uint32_t height,
 582                    uint32_t format, uint32_t flags)
 583 {
 584    return gbm->surface_create(gbm, width, height, format, flags, NULL, 0);
 585 }
 586
 587 GBM_EXPORT struct gbm_surface *
 588 gbm_surface_create_with_modifiers(struct gbm_device *gbm,
 589                                   uint32_t width, uint32_t height,
 590                                   uint32_t format,
 591                                   const uint64_t *modifiers,
 592                                   const unsigned int count)
 593 {
 594    if ((count && !modifiers) || (modifiers && !count)) {
 595       errno = EINVAL;
 596       return NULL;
 597    }
 598
 599    return gbm->surface_create(gbm, width, height, format, 0,
 600                               modifiers, count);
 601 }
 602
 603 /**
 604  * Destroys the given surface and frees all resources associated with
 605  * it.
 606  *
 607  * All buffers locked with gbm_surface_lock_front_buffer() should be
 608  * released prior to calling this function.
 609  *
 610  * \param surf The surface
 611  */
 612 GBM_EXPORT void
 613 gbm_surface_destroy(struct gbm_surface *surf)
 614 {
 615    surf->gbm->surface_destroy(surf);
 616 }
 617
 618 /**
 619  * Lock the surface's current front buffer
 620  *
 621  * Lock rendering to the surface's current front buffer until it is
 622  * released with gbm_surface_release_buffer().
 623  *
 624  * This function must be called exactly once after calling
 625  * eglSwapBuffers.  Calling it before any eglSwapBuffer has happened
 626  * on the surface or two or more times after eglSwapBuffers is an
 627  * error.  A new bo representing the new front buffer is returned.  On
 628  * multiple invocations, all the returned bos must be released in
 629  * order to release the actual surface buffer.
 630  *
 631  * \param surf The surface
 632  *
 633  * \return A buffer object that should be released with
 634  * gbm_surface_release_buffer() when no longer needed.  The implementation
 635  * is free to reuse buffers released with gbm_surface_release_buffer() so
 636  * this bo should not be destroyed using gbm_bo_destroy().  If an error
 637  * occurs this function returns %NULL.
 638  */
 639 GBM_EXPORT struct gbm_bo *
 640 gbm_surface_lock_front_buffer(struct gbm_surface *surf)
 641 {
 642    return surf->gbm->surface_lock_front_buffer(surf);
 643 }
 644
 645 /**
 646  * Release a locked buffer obtained with gbm_surface_lock_front_buffer()
 647  *
 648  * Returns the underlying buffer to the gbm surface.  Releasing a bo
 649  * will typically make gbm_surface_has_free_buffer() return 1 and thus
 650  * allow rendering the next frame, but not always. The implementation
 651  * may choose to destroy the bo immediately or reuse it, in which case
 652  * the user data associated with it is unchanged.
 653  *
 654  * \param surf The surface
 655  * \param bo The buffer object
 656  */
 657 GBM_EXPORT void
 658 gbm_surface_release_buffer(struct gbm_surface *surf, struct gbm_bo *bo)
 659 {
 660    surf->gbm->surface_release_buffer(surf, bo);
 661 }
 662
 663 /**
 664  * Return whether or not a surface has free (non-locked) buffers
 665  *
 666  * Before starting a new frame, the surface must have a buffer
 667  * available for rendering.  Initially, a gbm surface will have a free
 668  * buffer, but after one or more buffers have been locked (\sa
 669  * gbm_surface_lock_front_buffer()), the application must check for a
 670  * free buffer before rendering.
 671  *
 672  * If a surface doesn't have a free buffer, the application must
 673  * return a buffer to the surface using gbm_surface_release_buffer()
 674  * and after that, the application can query for free buffers again.
 675  *
 676  * \param surf The surface
 677  * \return 1 if the surface has free buffers, 0 otherwise
 678  */
 679 GBM_EXPORT int
 680 gbm_surface_has_free_buffers(struct gbm_surface *surf)
 681 {
 682    return surf->gbm->surface_has_free_buffers(surf);
 683 }