Re: [PATCH 1/4] Vectorize aio_read/aio_write methods

[Badari Pulavarty <pbadari@us.ibm.com>]

On Thu, 2006-05-11 at 11:47 -0700, Andrew Morton wrote:
> Badari Pulavarty <pbadari@us.ibm.com> wrote:
> >
> >  static ssize_t ep_aio_read_retry(struct kiocb *iocb)
> >  {
> >  	struct kiocb_priv	*priv = iocb->private;
> > -	ssize_t			status = priv->actual;
> > +	ssize_t			len, total;
> >  
> >  	/* we "retry" to get the right mm context for this: */
> > -	status = copy_to_user(priv->ubuf, priv->buf, priv->actual);
> > -	if (unlikely(0 != status))
> > -		status = -EFAULT;
> > -	else
> > -		status = priv->actual;
> > +
> > +	/* copy stuff into user buffers */
> > +	total = priv->actual;
> > +	len = 0;
> > +	for (i=0; i < priv->count; i++) {
> > +		ssize_t this = min(priv->iv[i].iov_len, total);
> > +
> > +		if (copy_to_user(priv->iv[i].iov_buf, priv->buf, this))
> > +			break;
> > +
> > +		total -= this;
> > +		len += this;
> > +		if (total <= 0)
> > +			break;
> > +	}
> > +
> > +	if (unlikely(len == 0))
> > +		len = -EFAULT;
> 
> This is still wrong, isn't it?  Or am I looking at the same patch?
> 
> There's no way in which `total' can go negative, so it'd be nicer to just
> test it for equality with zero.  Because if it goes unexpectedly negative,
> we _want_ the kernel to malfunction, rather than mysteriously covering
> things up.
> 
> The final test there should be
> 
> 	if (unlikely(total != 0))
> 
> yes?

No. The original check is correct - we want to return EFAULT if
copy_to_user() failed and we haven't copied anything so far.
If we copied anything so far, we should return, that many bytes.
(like short-io).


Thanks,
Badari