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: <fda2a3dd-b325-4780-bd02-d1fedcaec260@linux.microsoft.com>
Date:   Wed, 27 Sep 2023 17:17:54 -0700
From:   Nuno Das Neves <nunodasneves@...ux.microsoft.com>
To:     Greg KH <gregkh@...uxfoundation.org>, Wei Liu <wei.liu@...nel.org>
Cc:     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 9/27/2023 1:33 AM, Greg KH wrote:
> On Wed, Sep 27, 2023 at 08:04:42AM +0000, Wei Liu wrote:
>> So, the driver is supposed to stash a pointer to struct device in
>> private_data. That's what I alluded to in my previous reply. The core
>> driver framework or the VFS doesn't give us a reference to struct
>> device. We have to do it ourselves.
> 
> Please read Linux Device Drivers, 3rd edition, chapter 3, for how to do
> this properly.  The book is free online.
> 

Thanks, the issue that confused us was how to get the miscdevice.
I eventually found the answer in the misc_register() documentation:

"By default, an open() syscall to the device sets file->private_data to
point to the structure."

That's good - when we create a guest, we will have the miscdevice
in private_data already. Then we can just put it in our per-guest data
structure. That will let us retrieve the device in the other ioctls so 
we can call dev_*().

Thanks,
Nuno