al004046@anubis.uji.es said:
> gsfb_mmap(void *v, off_t offset, int prot) {
> 	if (GSFB_BUFFER_SIZE >= (unsigned) offset)
> 	    return NULL; 

I didn't look deeper, but this piece of code is wrong for two
reasons:
1. the comparision is reverted
2. returning NULL doesn't what you expect - probably you get
   the physical page at 0 mapped
   to return an error, use (-1)

best regards
Matthias