Re: [PATCH v2] usb: ffs: fix regression when quirk_ep_out_aligned_size flag is set

[Al Viro <viro@ZenIV.linux.org.uk>]

On Wed, Oct 08, 2014 at 02:12:18PM -0700, David Cohen wrote:
>  		use_mm(io_data->mm);
>  		for (i = 0; i < io_data->nr_segs; i++) {
> +			size_t len = min_t(size_t, ret - pos,
> +					io_data->iovec[i].iov_len);
> +			if (!len)
> +				break;
>  			if (unlikely(copy_to_user(io_data->iovec[i].iov_base,
> -						 &io_data->buf[pos],
> -						 io_data->iovec[i].iov_len))) {
> +						 &io_data->buf[pos], len))) {
>  				ret = -EFAULT;
>  				break;
>  			}
> -			pos += io_data->iovec[i].iov_len;
> +			pos += len;

Hmm...  This is really asking for something like
	if (copy_to_iter(io_data->buf, ret, <something>) != ret)
		ret = -EFAULT;
with <something> being an iov_iter instead of iovec.  It would be really
nice to have that thing switched to ->read_iter/->write_iter, dropping
->read/->write/->aio_read/->aio_write; I'm not familiar enough with that
code to do it on my own, though, so it would require some help from
maintainers...