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Date:   Wed, 27 Sep 2023 17:17:54 -0700
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Subject: Re: [PATCH v3 15/15] Drivers: hv: Add modules to expose /dev/mshv to
 VMMs running on Hyper-V
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To:     Greg KH <gregkh@linuxfoundation.org>, Wei Liu <wei.liu@kernel.org>
Cc:     linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
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        dave.hansen@linux.intel.com, hpa@zytor.com, will@kernel.org,
        catalin.marinas@arm.com
References: <2023092342-staunch-chafe-1598@gregkh>
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 <ZRPiGk9M3aQr99Y5@liuwe-devbox-debian-v2>
 <2023092757-cupbearer-cancel-b314@gregkh>
From:   Nuno Das Neves <nunodasneves@linux.microsoft.com>
In-Reply-To: <2023092757-cupbearer-cancel-b314@gregkh>
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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