Playing around with /dev/fb0

drawfb.c

#define _GNU_SOURCE

#include <fcntl.h>
#include <linux/fb.h>
#include <stddef.h>
#include <stdio.h>
#include <sys/ioctl.h>
#include <sys/mman.h>

int main() {
    int fd = open("/dev/fb0", O_RDWR);

    struct fb_fix_screeninfo fix_info;
    struct fb_var_screeninfo var_info;
    ioctl(fd, FBIOGET_FSCREENINFO, &fix_info);
    ioctl(fd, FBIOGET_VSCREENINFO, &var_info);
    printf("id = %s\n", fix_info.id);
    printf("smem_start = 0x%lx\n", fix_info.smem_start);
    printf("smem_len = 0x%lx\n", fix_info.smem_len);
    printf("res %dx%d, virtual res %dx%d\n", var_info.xres, var_info.yres, var_info.xres_virtual, var_info.yres_virtual);

    char *mem = mmap(NULL, fix_info.smem_len, PROT_READ | PROT_WRITE, MAP_SHARED, fd, fix_info.smem_start);
    while(1)
        for (size_t i = 0; i < fix_info.smem_len; i ++)
            mem[i] = i;
}