[PATCH] mmap returns EINVAL if len==0
mmap returns EINVAL when len==0,
while old kernel behaviour is to return addr in this case.
Though POSIX requires EINVAL in this case and it was
fixed in mainstream around ~2.6.16, we still
have to keep compatibility for some time with old stupid
apps like rpm which did exactly this and expected success :/
Bug #83938, #74964