[pushed] Prelimit number of bytes to read in "vFile:pread:"

[Gary Benson]

Pedro Alves wrote:
> On 08/19/2015 11:41 AM, Gary Benson wrote:
> > Pedro Alves wrote:
> > > The fact that Gary's chunk size limiting patch made things much
> > > faster on the nios2 board is still mysterious to me.  I'd expect
> > > the slowness to be latency bound, given the request/response
> > > nature of the RSP, but then I'd expect that more chunking would
> > > slow things down, not speed it up.
> > 
> > I think I figured this out...
> > 
> > While handling "vFile:pread:" packets, gdbserver would read the
> > number of bytes requested regardless of whether this would fit
> > into the reply packet.  gdbserver would then return a packet's
> > worth of data and discard the remainder.  When accessing large
> > binaries GDB (via BFD) routinely makes large "vFile:pread:"
> > requests, resulting in gdbserver allocating large unnecessary
> > buffers and reading some portions of the file many times over.
> > 
> > This commit causes gdbserver to limit the number of bytes to be
> > read to a sensible maximum prior to allocating buffers and reading
> > data.
> > 
> > Built and regtested on RHEL 6.6 x86_64.
> > 
> > May I push this to HEAD and to the branch?
> 
> OK.

Pushed to both.

Thanks,
Gary

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