linux-kernel - Re: [PATCH 02/15] hyperv: Add a function to detect hv

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Message-ID: <20161202064805.GA19267@kroah.com>
Date:   Fri, 2 Dec 2016 07:48:05 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     KY Srinivasan <kys@...rosoft.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
        "olaf@...fle.de" <olaf@...fle.de>,
        "apw@...onical.com" <apw@...onical.com>,
        "vkuznets@...hat.com" <vkuznets@...hat.com>,
        "jasowang@...hat.com" <jasowang@...hat.com>,
        "leann.ogasawara@...onical.com" <leann.ogasawara@...onical.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>
Subject: Re: [PATCH 02/15] hyperv: Add a function to detect hv_device

On Fri, Dec 02, 2016 at 06:02:29AM +0000, KY Srinivasan wrote:
> 
> 
> > -----Original Message-----
> > From: Greg KH [mailto:gregkh@...uxfoundation.org]
> > Sent: Thursday, December 1, 2016 12:36 PM
> > To: KY Srinivasan <kys@...rosoft.com>
> > Cc: linux-kernel@...r.kernel.org; devel@...uxdriverproject.org;
> > olaf@...fle.de; apw@...onical.com; vkuznets@...hat.com;
> > jasowang@...hat.com; leann.ogasawara@...onical.com; Haiyang Zhang
> > <haiyangz@...rosoft.com>
> > Subject: Re: [PATCH 02/15] hyperv: Add a function to detect hv_device

Ugh, please fix your email client...

> > 
> > On Thu, Dec 01, 2016 at 09:28:39AM -0800, kys@...hange.microsoft.com
> > wrote:
> > > From: Haiyang Zhang <haiyangz@...rosoft.com>
> > >
> > > Signed-off-by: Haiyang Zhang <haiyangz@...rosoft.com>
> > > Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> > > ---
> > >  drivers/hv/vmbus_drv.c |    6 ++++++
> > >  include/linux/hyperv.h |    2 ++
> > >  2 files changed, 8 insertions(+), 0 deletions(-)
> > >
> > > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> > > index 0276d2e..1730ac0 100644
> > > --- a/drivers/hv/vmbus_drv.c
> > > +++ b/drivers/hv/vmbus_drv.c
> > > @@ -692,6 +692,12 @@ struct onmessage_work_context {
> > >  	struct hv_message msg;
> > >  };
> > >
> > > +bool device_is_hyperv(struct device *dev)
> > > +{
> > > +	return dev->release == vmbus_device_release;
> > > +}
> > > +EXPORT_SYMBOL_GPL(device_is_hyperv);
> > 
> > Wait, eek, no!  That's NOT how you determine a device type, if you
> > really even ever need to do that.
> > 
> > Why are you needing this?  You should always "just know" what type of
> > device a struct device * is, that's what we rely on in the driver model.
> > Otherwise things get messy very very quickly.
> > 
> > Sorry, I can't take this without a ton of justification, and even then,
> > you need to do this correctly (and no, I'm not going to tell you how to
> > do that as I don't like it being done...)
> > 
> Greg,
> 
> To support SR-IOV, netvsc registers for all netdev events. For netdev events related to the
> VF interface, we need to do some special processing. And so, we need to determine
> if the device that is generating the netdev event is Hyper-V device or not
> (passed through the PCI pass through driver). Is this justification sufficient.
> As you have observed, currently there is no user of this API and that is because netvsc
> will be the user. To avoid cross-tree dependency, we wanted to get this functionality in first
> before submitting the netvsc patch.

See, you do have some text for a changelog!

{grumble...}

No, I don't think this is a good justification, where are you going to
put this "check" into the networking stack?  Your driver should only be
binding to devices of this "type" anyway, so by that logic, it already
"knows" that the device is of this type.

In other words, why do you need this and PCI or USB doesn't?  Why is
hyperv "special"?

greg k-h