linux-kernel - Re: [PATCH] virtio-blk: Fix kconfig option

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Message-ID: <20120906101842.GB32325@redhat.com>
Date:	Thu, 6 Sep 2012 13:18:43 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Kent Overstreet <koverstreet@...gle.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] virtio-blk: Fix kconfig option

On Thu, Sep 06, 2012 at 03:02:48AM -0700, Kent Overstreet wrote:
> On Thu, Sep 06, 2012 at 12:49:56PM +0300, Michael S. Tsirkin wrote:
> > On Thu, Sep 06, 2012 at 02:25:12AM -0700, Kent Overstreet wrote:
> > > On Thu, Sep 06, 2012 at 11:44:03AM +0300, Michael S. Tsirkin wrote:
> > > > On Thu, Sep 06, 2012 at 12:41:13AM -0700, Kent Overstreet wrote:
> > > > > On Tue, Sep 04, 2012 at 03:53:53PM +0930, Rusty Russell wrote:
> > > > > > Kent Overstreet <koverstreet@...gle.com> writes:
> > > > > > 
> > > > > > > CONFIG_VIRTIO isn't exposed, everything else is supposed to select it
> > > > > > > instead.
> > > > > > 
> > > > > > This is a slight mis-understanding.  It's supposed to be selected by
> > > > > > the particular driver, probably virtio_pci in your case.
> > > > > 
> > > > > So are you saying virtio-blk depends on virtio-pci? If so, the kconfig
> > > > > should have that.
> > > > > 
> > > > > As is, VIRTIO_BLK just has:
> > > > > 	depends on EXPERIMENTAL && VIRTIO
> > > > > 
> > > > > which is flat out broken.
> > > > 
> > > > I don't think anything is broken.
> > > > Can you show an example of a broken configuration?
> > > 
> > > Do you not understand the difference between depends an selects?
> > > Or did you not read my original mail?
> > > Flip off everything in drivers -> virtio
> > > 
> > > Now go to drivers -> block and try to turn on virtio-blk.
> > > 
> > > It's not listed!
> > 
> > Yes. Because you disabled all virtio backends.
> > It does not make sense to have any frontends.
> 
> How's a user - or even another kernel developer who isn't familiar with
> virtio - supposed to know that?
> 
> I still don't know what exactly a virtio backend is - the term isn't
> even mentioned anywhere that I've seen.
> 
> Whatever it is though virtio-blk should be depending on _that_, not a
> config option that _isn't exposed in the menu_!
> 
> > > Now go back to drivers -> virtio and turn on (randomly) balloon.
> > > 
> > > Go back to drivers -> block, and now you can turn on virtio-blk!
> > > 
> > > Do you see what's wrong with this picture?
> > 
> > Yes. You got unlucky with your random guess.
> > It's a bug in balloon kconfig: it should not
> > select virtio.
> > I sent a patch to fix that yesterday.
> 
> Then it's also a bug in the comments at the top of
> drivers/virtio/Kconfig.
> 
> And besides that, how the _hell_ is a user supposed to know to turn on
> VIRTIO_PCI before VIRTIO_BLK? It's not documented anywhere (if that is
> what's supposed to happen! I still don't know)

Well, what kind of device do you have? Tell us :)
If it's a virtio pci device,
you need to enable virtio-pci and virtio-blk.

> and even if it was
> documented, having one kconfig option depend on something that's exposed
> in a _completely different menu_ is just made of fail.

Fine, but why pick on virtio?
This is extremely common in kconfig.
For example, a ton of network drivers depend
on PCI, it's exactly the same thing.


-- 
MST
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