[Libguestfs] [PATCH nbdkit] python: Simulate slow extents

[Nir Soffer]

On Wed, Jan 20, 2021 at 10:35 PM Richard W.M. Jones <rjones at redhat.com>
wrote:

> On Wed, Jan 20, 2021 at 09:12:58PM +0200, Nir Soffer wrote:
> > In some situations getting image extents can be slow. Add configuration
> > value to simulate slow extents. This can be useful for testing and
> > optimizing nbd clients.
> >
> > Example usage - simulating 1 seconds delay:
> >
> > qemu-img create -f raw test.img 10g
> >
> > ./nbdkit -f -v python ./plugins/python/examples/file.py \
> >     file=test.img extents_delay=1 2>&1 | grep 'python: extents'
>
> Sorry, I meant to send you a follow-up email about using the delay
> filter for this testing, and didn't get around to it.  It is possible
> to do this already by putting the delay filter over and controlling
> the extents delay.  Something like:
>
>   ./nbdkit -f -v --filter=delay \
>       python ./plugins/python/examples/file.py \
>       file=test.img delay-extents=1
>

Nice


>
> ---
>
> What is the purpose of yield() here?
>

This returns a generator that will return one
item in the caller. Could be also:

    return [(offset, count, 0)]


>
> > +def extents(h, count, offset, flags):
> > +    time.sleep(extents_delay)
> > +    yield (offset, count, 0)
>
> Rich.
>
> --
> Richard Jones, Virtualization Group, Red Hat
> http://people.redhat.com/~rjones
> Read my programming and virtualization blog: http://rwmj.wordpress.com
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>
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