On Friday 09 July 2010 22:59:06 Daniel Jacobowitz wrote:

> On Fri, Jul 09, 2010 at 10:54:07PM +0400, Vladimir Prus wrote:
> > On Wednesday 07 July 2010 20:29:55 Daniel Jacobowitz wrote:
> > 
> > > > -           if (xfer == 0)
> > > > -             return xfered;
> > > > -           if (xfer < 0)
> > > > -             {
> > > > -               remaining = half;               
> > > > -             }
> > > > -           else
> > > > -             {
> > > > -               /* We have successfully read the first half.  So, the
> > > > -                  error must be in the second half.  Adjust start and
> > > > -                  remaining to point at the second half.  */
> > > > -               xfered += xfer;
> > > > -               start += xfer;
> > > > -               remaining -= xfer;
> > > > -             }
> > > > -           half = remaining/2;
> > > > +           xfree (buffer);
> > > > +           xfered += to_read;
> > > >           }
> > > 
> > > Why do we skip to_read bytes if we succeed at reading zero bytes?
> > > For that matter, what does a return value of zero mean?  It seems like
> > > this would mean the same as -1.
> > 
> > I am not really sure. Per documentation of target_read:
> > 
> >    Return the number of bytes actually transfered, or -1 if the
> >    transfer is not supported or otherwise fails.  Return of a positive
> >    value less than LEN indicates that no further transfer is possible.
> > 
> > So, value of 0 seems to mean 'there are no more bytes that that, honest', 
> > and that we probably don't need to try further. Documentation for
> > to_xfer_partial seem to give such meaning to return of 0.
> 
> I'd suggest treating 0 and -1 the same, for memory.
> 
> > On the
> > other hand, it's not clear what return value of <LEN might mean,
> > and whether we should try to read remaining chunk. What would you suggest?
> 
> A return of less than LEN from xfer_partial doesn't mean anything; you
> just retry.  A return of less than LEN from target_read, though, is
> supposed to mean that there is no point in retrying; the next byte is
> inaccessible or does not exist.
> 
> It doesn't look like memory reads (unlike other partial transfers)
> implement that; usually they just fail.  But we can treat it that way
> anyway.  So <LEN means we got some number of bytes, and then we should
> see what happens after those successful bytes.

Here's a revised version.


Thanks,

-- 
Vladimir Prus
CodeSourcery
vladimir@codesourcery.com
(650) 331-3385 x722