linux-kernel - Re: [PATCH v3 15/15] Drivers: hv: Add modules to expose /dev/mshv to VMMs running on Hyper-V

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Message-ID: <2023092646-version-series-a7b5@gregkh>
Date:   Tue, 26 Sep 2023 10:03:31 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Wei Liu <wei.liu@...nel.org>
Cc:     Nuno Das Neves <nunodasneves@...ux.microsoft.com>,
        linux-hyperv@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arch@...r.kernel.org, patches@...ts.linux.dev,
        mikelley@...rosoft.com, kys@...rosoft.com, haiyangz@...rosoft.com,
        decui@...rosoft.com, apais@...ux.microsoft.com,
        Tianyu.Lan@...rosoft.com, ssengar@...ux.microsoft.com,
        mukeshrathor@...rosoft.com, stanislav.kinsburskiy@...il.com,
        jinankjain@...ux.microsoft.com, vkuznets@...hat.com,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, hpa@...or.com, will@...nel.org,
        catalin.marinas@....com
Subject: Re: [PATCH v3 15/15] Drivers: hv: Add modules to expose /dev/mshv to
 VMMs running on Hyper-V

On Tue, Sep 26, 2023 at 07:00:51AM +0000, Wei Liu wrote:
> On Tue, Sep 26, 2023 at 08:31:03AM +0200, Greg KH wrote:
> > On Tue, Sep 26, 2023 at 05:54:34AM +0000, Wei Liu wrote:
> > > On Tue, Sep 26, 2023 at 06:52:46AM +0200, Greg KH wrote:
> > > > On Mon, Sep 25, 2023 at 05:07:24PM -0700, Nuno Das Neves wrote:
> > > > > On 9/23/2023 12:58 AM, Greg KH wrote:
> > > > > > Also, drivers should never call pr_*() calls, always use the proper
> > > > > > dev_*() calls instead.
> > > > > > 
> > > > > 
> > > > > We only use struct device in one place in this driver, I think that is the
> > > > > only place it makes sense to use dev_*() over pr_*() calls.
> > > > 
> > > > Then the driver needs to be fixed to use struct device properly so that
> > > > you do have access to it when you want to print messages.  That's a
> > > > valid reason to pass around your device structure when needed.
> > > 
> > > Greg, ACRN and Nitro drivers do not pass around the device structure.
> > > Instead, they rely on a global struct device. We can follow the same.
> > 
> > A single global struct device is wrong, please don't do that.
> > 
> > Don't copy bad design patterns from other drivers, be better :)
> > 
> 
> If we're working with real devices like network cards or graphics cards
> I would agree -- it is easy to imagine that we have several cards of the
> same model in the system -- but in real world there won't be two
> hypervisor instances running on the same hardware.
> 
> We can stash the struct device inside some private data fields, but that
> doesn't change the fact that we're still having one instance of the
> structure. Is this what you want? Or do you have something else in mind?

You have a real device, it's how userspace interacts with your
subsystem.  Please use that, it is dynamically created and handled and
is the correct representation here.

thanks,

greg k-h