Linux framebuffer example

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <linux/fb.h>
#include <sys/mman.h>
struct fb_fix_screeninfo FixedInfo;
struct fb_var_screeninfo OrigVarInfo;
static int FrameBufferFD = -1;
void *FrameBuffer = (void *) -1;
void test(void) {
/* open the framebuffer device */
FrameBufferFD = open("/dev/fb0", O_RDWR);
if (FrameBufferFD < 0) {
fprintf(stderr, "Error opening /dev/fb0/n");
exit(1);
}
/* Get the fixed screen info */
if (ioctl(FrameBufferFD, FBIOGET_FSCREENINFO, &FixedInfo)) {
fprintf(stderr, "error: ioctl(FBIOGET_FSCREENINFO) failed/n");
exit(1);
}
/* get the variable screen info */
if (ioctl(FrameBufferFD, FBIOGET_VSCREENINFO, &OrigVarInfo)) {
fprintf(stderr, "error: ioctl(FBIOGET_VSCREENINFO) failed/n");
exit(1);
}

if (FixedInfo.visual != FB_VISUAL_TRUECOLOR && FixedInfo.visual != FB_VISUAL_DIRECTCOLOR) {
fprintf(stderr, "non-TRUE/DIRECT-COLOR visuals (0x%x) not supported by this demo./n", FixedInfo.visual);
exit(1);
}
/*
* fbdev says the frame buffer is at offset zero, and the mmio region
* is immediately after.
*/
/* mmap the framebuffer into our address space */
FrameBuffer = (void *) mmap(0, /* start */
FixedInfo.smem_len, /* bytes */
PROT_READ | PROT_WRITE, /* prot */
MAP_SHARED, /* flags */
FrameBufferFD, /* fd */
0 /* offset */);
if (FrameBuffer == (void *) - 1) {
fprintf(stderr, "error: unable to mmap framebuffer/n");
exit(1);
}
}
void close(void) {
munmap(FrameBuffer, FixedInfo.smem_len);
close(FrameBufferFD);
}
int main() {
test();
fprintf(stderr, "openFBDEV finish/n");
memset(FrameBuffer, 128, FixedInfo.smem_len);
sleep(5);
close();
fprintf(stderr, "closeFBDEV finish/n");
return 0;
}