linux-kernel - Re: [RFC PATCH v2] ptp: Add vDSO-style vmclock support

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Message-ID: <9b33c44f-3855-4c7e-925e-2f4af3b0567a@opensynergy.com>
Date: Fri, 5 Jul 2024 10:12:21 +0200
From: Peter Hilber <peter.hilber@...nsynergy.com>
To: David Woodhouse <dwmw2@...radead.org>, linux-kernel@...r.kernel.org,
 virtualization@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
 linux-rtc@...r.kernel.org, "Ridoux, Julien" <ridouxj@...zon.com>,
 virtio-dev@...ts.linux.dev, "Luu, Ryan" <rluu@...zon.com>,
 "Chashper, David" <chashper@...zon.com>
Cc: "Christopher S. Hall" <christopher.s.hall@...el.com>,
 Jason Wang <jasowang@...hat.com>, John Stultz <jstultz@...gle.com>,
 "Michael S. Tsirkin" <mst@...hat.com>, netdev@...r.kernel.org,
 Richard Cochran <richardcochran@...il.com>, Stephen Boyd <sboyd@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, Xuan Zhuo
 <xuanzhuo@...ux.alibaba.com>, Marc Zyngier <maz@...nel.org>,
 Mark Rutland <mark.rutland@....com>,
 Daniel Lezcano <daniel.lezcano@...aro.org>,
 Alessandro Zummo <a.zummo@...ertech.it>,
 Alexandre Belloni <alexandre.belloni@...tlin.com>
Subject: Re: [RFC PATCH v2] ptp: Add vDSO-style vmclock support

On 03.07.24 12:40, David Woodhouse wrote:

[...]

> 
> 
> This is what I currently have for 'struct vmclock_abi' that I'd like to
> persuade you to adopt. I need to tweak it some more, for at least the
> following reasons, as well as any more you can see:
> 
>  • size isn't big enough for 64KiB pages
>  • Should be explicitly little-endian
>  • Does it need esterror as well as maxerror?

I have no opinion about this. I can drop esterror if unwanted.

>  • Why is maxerror in picoseconds? It's the only use of that unit
>  • Where do the clock_status values come from? Do they make sense?
>  • Are signed integers OK? (I think so!).

Signed integers would need to be introduced to Virtio, which so far only
uses explicitly unsigned types: u8, le16 etc.