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Re: [Xen-devel] blk[front|back] does not hand over disk parameters

To: "Adi Kriegisch" <adi@xxxxxxxxxxxxxxx>, "Ian Campbell" <Ian.Campbell@xxxxxxxxxx>
Subject: Re: [Xen-devel] blk[front|back] does not hand over disk parameters
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Mon, 28 Feb 2011 10:55:12 +0000
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>>> On 28.02.11 at 11:06, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> This is not the sort of thing which changes dynamically across the
> lifetime of a device, is it? In which case it seems like the sort of
> information which the backend could communicate to the frontend via
> xenbus at start of day. e.g. take a look at how the sector-size is
> passed through xenbus. 
> 
> It should be trivial to add this in a compatible manner since the
> frontend can just do what it does today if the nodes are missing and the
> backend wouldn't rely on the frontend doing anything useful with the
> information anyway.

Am I right in understanding that these numbers aren't used by
the block layer itself at all, but just get provided to userspace for
whatever optimization it can do? In that case, I can't really see
how passing through these values can really help general
performance (i.e. for apps not paying attention to these values).

Confused, Jan


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