getfb.c revision 6b2c0e5854625cd0422c12c331dd22a3e3021079 
1// Copyright (c) 2012 The Chromium OS Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5#include <fcntl.h>
6#include <linux/fb.h>
7#include <stdint.h>
8#include <stdio.h>
9#include <stdlib.h>
10#include <sys/mman.h>
11#include <sys/ioctl.h>
12#include <unistd.h>
13
14int main(int argc, char *argv[])
15{
16  const char* device_name = "/dev/fb0";
17  struct fb_var_screeninfo info;
18  uint32_t screen_size = 0;
19  void *ptr = NULL;
20  int fd = -1;
21  FILE *file = NULL;
22  int ret = -1;
23
24  if (argc < 2) {
25    printf("Usage: getfb [filename]\n");
26    printf("Writes the active framebuffer to output file [filename].\n");
27    return 0;
28  }
29
30  // Open the file for reading and writing
31  fd = open(device_name, O_RDONLY);
32  if (fd == -1) {
33    fprintf(stderr, "Cannot open framebuffer device %s\n", device_name);
34    goto exit;
35  }
36  printf("The framebuffer device was opened successfully.\n");
37
38  // Get fixed screen information
39  if (ioctl(fd, FBIOGET_VSCREENINFO, &info) == -1) {
40    fprintf(stderr, "Error reading variable screen information.\n");
41    goto exit;
42  }
43
44  printf("%dx%d, %dbpp\n", info.xres, info.yres, info.bits_per_pixel);
45
46  // Figure out the size of the screen in bytes
47  screen_size = info.xres * info.yres * info.bits_per_pixel / 8;
48
49  // Map the device to memory
50  ptr = mmap(0, screen_size, PROT_READ, MAP_SHARED, fd, 0);
51  if (ptr == MAP_FAILED) {
52    fprintf(stderr, "Error: failed to map framebuffer device to memory.\n");
53    goto exit;
54  }
55  printf("The framebuffer device was mapped to memory successfully.\n");
56
57  // Write it to output file.
58  file = fopen(argv[1], "w");
59  if (!file) {
60    fprintf(stderr, "Could not open file %s for writing.\n", argv[1]);
61    goto exit;
62  }
63
64  if (fwrite(ptr, screen_size, 1, file) < 1) {
65    fprintf(stderr, "Error while writing framebuffer to file.\n");
66    goto exit;
67  }
68
69  ret = 0;
70
71exit:
72  if (file)
73    fclose(file);
74
75  if (ptr != MAP_FAILED && ptr)
76    munmap(ptr, screen_size);
77
78  if (fd >= 0)
79    close(fd);
80
81  return ret;
82}
83