linux-kernel - Re: [PATCH] virtio-blk: allow toggling host cache between writeback and writethrough

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Message-ID: <87boj4ps9o.fsf@rustcorp.com.au>
Date:	Wed, 25 Jul 2012 10:32:27 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Sasha Levin <levinsasha928@...il.com>,
	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH] virtio-blk: allow toggling host cache between writeback and writethrough

On Thu, 05 Jul 2012 09:02:23 +0200, Sasha Levin <levinsasha928@...il.com> wrote:
> On Thu, 2012-07-05 at 08:47 +0200, Paolo Bonzini wrote:
> > Il 04/07/2012 23:11, Sasha Levin ha scritto:
> > > There are two things going on here:
> > >  1. Rename VIRTIO_BLK_F_FLUSH to VIRTIO_BLK_F_WCE
> > >  2. Add a new VIRTIO_BLK_F_CONFIG_WCE
> > > 
> > > I'm concerned that the first change is going to break compilation for
> > > any code that included linux/virtio-blk.h and used VIRTIO_BLK_F_FLUSH.
> > 
> > That would be nlkt, right? :)
> 
> nlkt, lguest, and probably others.
> 
> linux/virtio_blk.h is a public kernel header, which is supposed to be
> used from userspace - so I assume many others who implemented virtio-blk
> for any reason took advantage of that header.

BTW, I have patched this myself now:

From: Rusty Russell <rusty@...tcorp.com.au>
Subject: virtio-blk: return VIRTIO_BLK_F_FLUSH to header.

This got renamed and clarified, but let's not break any userspace out there.

Signed-off-by: Rusty Russell <rusty@...tcorp.com.au>
---
 include/linux/virtio_blk.h |    5 +++++
 1 file changed, 5 insertions(+)

diff --git a/include/linux/virtio_blk.h b/include/linux/virtio_blk.h
--- a/include/linux/virtio_blk.h
+++ b/include/linux/virtio_blk.h
@@ -41,6 +41,11 @@
 #define VIRTIO_BLK_F_TOPOLOGY	10	/* Topology information is available */
 #define VIRTIO_BLK_F_CONFIG_WCE	11	/* Writeback mode available in config */
 
+#ifndef __KERNEL__
+/* Old (deprecated) name for VIRTIO_BLK_F_WCE. */
+#define VIRTIO_BLK_F_FLUSH VIRTIO_BLK_F_WCE
+#endif
+
 #define VIRTIO_BLK_ID_BYTES	20	/* ID string length */
 
 struct virtio_blk_config {
--
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