buffer.c

#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mman.h>
#include <time.h>
#include <unistd.h>

#include "buffer.h"

static void randname(char *buf) {
  struct timespec ts;
  clock_gettime(CLOCK_REALTIME, &ts);
  long r = ts.tv_nsec;
  for (int i = 0; i < 6; ++i) {
    buf[i] = 'A' + (r & 15) + (r & 16) * 2;
    r >>= 5;
  }
}

static int anonymous_shm_open(void) {
  char name[] = "/wooz-XXXXXX";
  int retries = 100;

  do {
    randname(name + strlen(name) - 6);

    --retries;
    // shm_open guarantees that O_CLOEXEC is set
    int fd = shm_open(name, O_RDWR | O_CREAT | O_EXCL, 0600);
    if (fd >= 0) {
      shm_unlink(name);
      return fd;
    }
  } while (retries > 0 && errno == EEXIST);

  return -1;
}

static int create_shm_file(off_t size) {
  int fd = anonymous_shm_open();
  if (fd < 0) {
    return fd;
  }

  if (ftruncate(fd, size) < 0) {
    close(fd);
    return -1;
  }

  return fd;
}

struct wooz_buffer *create_buffer(struct wl_shm *shm, enum wl_shm_format format,
                                  int32_t width, int32_t height,
                                  int32_t stride) {
  size_t size = stride * height;

  int fd = create_shm_file(size);
  if (fd == -1) {
    return NULL;
  }

  void *data = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
  if (data == MAP_FAILED) {
    close(fd);
    return NULL;
  }

  struct wl_shm_pool *pool = wl_shm_create_pool(shm, fd, size);
  struct wl_buffer *wl_buffer =
      wl_shm_pool_create_buffer(pool, 0, width, height, stride, format);
  wl_shm_pool_destroy(pool);

  close(fd);

  struct wooz_buffer *buffer = calloc(1, sizeof(struct wooz_buffer));
  buffer->wl_buffer = wl_buffer;
  buffer->data = data;
  buffer->width = width;
  buffer->height = height;
  buffer->stride = stride;
  buffer->size = size;
  buffer->format = format;
  return buffer;
}

void destroy_buffer(struct wooz_buffer *buffer) {
  if (buffer == NULL) {
    return;
  }
  munmap(buffer->data, buffer->size);
  wl_buffer_destroy(buffer->wl_buffer);
  free(buffer);
}