From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from linux.microsoft.com (linux.microsoft.com [13.77.154.182]) by smtp.subspace.kernel.org (Postfix) with ESMTP id AD6C2405F6 for ; Tue, 26 Sep 2023 21:52:30 +0000 (UTC) Received: from [10.0.0.178] (c-76-135-56-23.hsd1.wa.comcast.net [76.135.56.23]) by linux.microsoft.com (Postfix) with ESMTPSA id 8203520B74C0; Tue, 26 Sep 2023 14:52:29 -0700 (PDT) DKIM-Filter: OpenDKIM Filter v2.11.0 linux.microsoft.com 8203520B74C0 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux.microsoft.com; s=default; t=1695765150; bh=lBG32VN1WPmUQfi9u2u2mI5suzZ9jPlIJsDL8oCoWFk=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=RUOHflWoCL1yJo7QG8SpRsR0JvJ63uqX6NBElJV56MVeITu5dsEGJsz3hwa2VuaUa InGza+C1Ui7v+F6YyVYOVwSOwcC5HN47dcLP61XUtdTvTrZBi8YIFNNoGJ1XXkBNgX 615SLGTwD3n9Y+JYCaIz0XsLp7lT6Lhb/0bwl0R4= Message-ID: <05119cbc-155d-47c5-ab21-e6a08eba5dc4@linux.microsoft.com> Date: Tue, 26 Sep 2023 14:52:36 -0700 Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 15/15] Drivers: hv: Add modules to expose /dev/mshv to VMMs running on Hyper-V Content-Language: en-US To: Greg KH , Wei Liu Cc: linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org, x86@kernel.org, linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, patches@lists.linux.dev, mikelley@microsoft.com, kys@microsoft.com, haiyangz@microsoft.com, decui@microsoft.com, apais@linux.microsoft.com, Tianyu.Lan@microsoft.com, ssengar@linux.microsoft.com, mukeshrathor@microsoft.com, stanislav.kinsburskiy@gmail.com, jinankjain@linux.microsoft.com, vkuznets@redhat.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, hpa@zytor.com, will@kernel.org, catalin.marinas@arm.com References: <1695407915-12216-1-git-send-email-nunodasneves@linux.microsoft.com> <1695407915-12216-16-git-send-email-nunodasneves@linux.microsoft.com> <2023092342-staunch-chafe-1598@gregkh> <2023092630-masculine-clinic-19b6@gregkh> <2023092614-tummy-dwelling-7063@gregkh> <2023092646-version-series-a7b5@gregkh> From: Nuno Das Neves In-Reply-To: <2023092646-version-series-a7b5@gregkh> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 9/26/2023 1:03 AM, Greg KH wrote: > 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. >>>> What is the tangible benefit of using dev_*() over pr_*()? As I said, our use of struct device is very limited compared to all the places we may need to log errors. pr_*() is used by many, many drivers; it seems to be the norm. We can certainly add a pr_fmt to improve the logging. >>>> 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 :) >>> What makes it a bad pattern? It seems to be well-established, and is also used by KVM which this driver is loosely modeled after: https://elixir.bootlin.com/linux/v6.5.5/source/virt/kvm/kvm_main.c#L5128 >> >> 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. > Are you referring to the struct device we get from calling misc_register? If not, please be more specific. How would you suggest we get a reference to that device via e.g. open() or ioctl() without keeping a global reference to it? Thanks, Nuno