[xfs-masters] Re: [PATCH -mm 4/10][RFC] aio: convert aio_complete to file_endio_t

[David Brownell <david-b@xxxxxxxxxxx>]

On Monday 15 January 2007 5:54 pm, Nate Diller wrote:
> --- a/drivers/usb/gadget/inode.c      2007-01-12 14:42:29.000000000 -0800
> +++ b/drivers/usb/gadget/inode.c      2007-01-12 14:25:34.000000000 -0800
> @@ -559,35 +559,32 @@ static int ep_aio_cancel(struct kiocb *i
>       return value;
>  }
>  
> -static ssize_t ep_aio_read_retry(struct kiocb *iocb)
> +static int ep_aio_read_retry(struct kiocb *iocb)
>  {
>       struct kiocb_priv       *priv = iocb->private;
> -     ssize_t                 len, total;
> -     int                     i;
> +     ssize_t                 total;
> +     int                     i, err = 0;
>  
>       /* we "retry" to get the right mm context for this: */
>  
>       /* copy stuff into user buffers */
>       total = priv->actual;
> -     len = 0;
>       for (i=0; i < priv->nr_segs; i++) {
>               ssize_t this = min((ssize_t)(priv->iv[i].iov_len), total);
>  
>               if (copy_to_user(priv->iv[i].iov_base, priv->buf, this)) {
> -                     if (len == 0)
> -                             len = -EFAULT;
> +                     err = -EFAULT;

Discarding the capability to report partial success, e.g. that the first N
bytes were properly transferred?  I don't see any virtue in that change.
Quite the opposite in fact.

I think you're also expecting that if N bytes were requested, that's always
how many will be received.  That's not true for packetized I/O such as USB
isochronous transfers ... where it's quite legit (and in some cases routine)
for the other end to send packets that are shorter than the maximum allowed.
Sending a zero length packet is not the same as sending no packet at all,
for another example.