linux-kernel - Re: [patch 20/20] XEN-paravirt: Add Xen virtual block device driver.

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Message-ID: <C1CFD49A.7286%Keir.Fraser@cl.cam.ac.uk>
Date:	Sun, 14 Jan 2007 12:37:46 +0000
From:	Keir Fraser <Keir.Fraser@...cam.ac.uk>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>,
	Jeremy Fitzhardinge <jeremy@...p.org>
CC:	Andrew Morton <akpm@...l.org>, <virtualization@...ts.osdl.org>,
	<xen-devel@...ts.xensource.com>,
	Chris Wright <chrisw@...s-sol.org>,
	Ian Pratt <ian.pratt@...source.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [patch 20/20] XEN-paravirt: Add Xen virtual block device
 driver.

On 14/1/07 11:05 am, "Jan Engelhardt" <jengelh@...ux01.gwdg.de> wrote:

>> The block device frontend driver allows the kernel to access block
>> devices exported exported by a virtual machine containing a physical
>> block device driver.
> 
> Is this significantly different from ubd/hostfs that it actually warrants a
> reinvention?

It is certainly unlike hostfs because hostfs provides file-level access to
host storage, not block-level. It's unlike both ubd and hostfs in that both
of those (I believe) make significant use of the syscall interface (and so
assume they run in a process on a Linux host). Also our driver appears to be
lower level, pushing more responsibility for features like CoW into the VMM.
Arguably that's a more generically reusable and flexible strategy although
it requires more VMM run-time support (which a Xen system provides).

>> + (void)xenbus_switch_state(info->xbdev, XenbusStateConnected);
> 
> Cast remove, if xenbus_switch_state does not have __must_check.
> Also elsewhere.

Okay, we should certainly follow the general rule here.

 Thanks,
 Keir

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