[libvirt] [PATCH 25/27] fdstream: Suppress use of IO helper for sparse streams

[Daniel P. Berrange]

On Thu, Apr 28, 2016 at 12:05:12PM +0200, Michal Privoznik wrote:
> This is kind of a hacky approach to the following problem, but so
> far I am unable to come up with anything better. On some
> occasions (esp. when dealing with regular files) libvirt_iohelper
> is spawned to prefetch data for us. We will then have a pipe then
> for reading the data from it. This does not fit in our sparse
> stream implementation as one simply doesn't lseek() over a pipe.
> Until this is resolved, let's suppress use of the IO helper and
> read data from FD directly.

This doesn't really fly - the problem is that with regular files,
poll() on the FD will always return ready, even if the read or
write will block in I/O. So by nomt using the iohelper this is
going to cause our main loop to block on I/O for streams.

Regards,
Daniel
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