netdev - Re: [PATCH -mm 4/10][RFC] aio: convert aio_complete to file_endio

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Date:	Tue, 16 Jan 2007 01:21:24 -0800
From:	"Nate Diller" <nate.diller@...il.com>
To:	"David Brownell" <david-b@...bell.net>
Cc:	"Nate Diller" <nate@...mi.com>, "Andrew Morton" <akpm@...l.org>,
	"Alan Cox" <alan@...rguk.ukuu.org.uk>,
	"Trond Myklebust" <trond.myklebust@....uio.no>,
	"Benjamin LaHaise" <bcrl@...ck.org>,
	"Alexander Viro" <viro@...iv.linux.org.uk>,
	"Suparna Bhattacharya" <suparna@...ibm.com>,
	"Kenneth W Chen" <kenneth.w.chen@...el.com>,
	"David Brownell" <dbrownell@...rs.sourceforge.net>,
	"Christoph Hellwig" <hch@...radead.org>,
	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	netdev@...r.kernel.org, ocfs2-devel@....oracle.com,
	linux-aio@...ck.org, xfs-masters@....sgi.com
Subject: Re: [PATCH -mm 4/10][RFC] aio: convert aio_complete to file_endio_t

On 1/15/07, David Brownell <david-b@...bell.net> wrote:
> 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.

I will convert this (usb) code to use the standard completion path,
which you will notice *gained* the ability to properly report both an
error and a partial success as part of this patch.  In fact, fixing
this up was my intention when I wrote this patch, and the later patch
was a compromise intended to get this whole bundle out for review in a
timely manner :)

NATE
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