netdev - Re: [PATCH v7] posix-timers: add clock

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Message-ID: <CAF2d9jjA8iM1AoPUhQPK62tdd7gPnCnt51f_NMhOAs546rU3dA@mail.gmail.com>
Date: Mon, 1 Apr 2024 22:42:47 -0700
From: Mahesh Bandewar (महेश बंडेवार) <maheshb@...gle.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: Sagi Maimon <maimon.sagi@...il.com>, richardcochran@...il.com, luto@...nel.org, 
	mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com, x86@...nel.org, 
	hpa@...or.com, arnd@...db.de, geert@...ux-m68k.org, peterz@...radead.org, 
	hannes@...xchg.org, sohil.mehta@...el.com, rick.p.edgecombe@...el.com, 
	nphamcs@...il.com, palmer@...ive.com, keescook@...omium.org, 
	legion@...nel.org, mark.rutland@....com, mszeredi@...hat.com, 
	casey@...aufler-ca.com, reibax@...il.com, davem@...emloft.net, 
	brauner@...nel.org, linux-kernel@...r.kernel.org, linux-api@...r.kernel.org, 
	linux-arch@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH v7] posix-timers: add clock_compare system call

On Mon, Apr 1, 2024 at 1:46 PM Thomas Gleixner <tglx@...utronix.de> wrote:
>
> Sagi!
>
> On Thu, Mar 28 2024 at 17:40, Sagi Maimon wrote:
> > On Sat, Mar 23, 2024 at 2:38 AM Thomas Gleixner <tglx@...utronix.de> wrote:
> >> On top this needs an analyis whether any of the gettimex64()
> >> implementations does something special instead of invoking the
> >> ptp_read_system_prets() and ptp_read_system_postts() helpers as close as
> >> possible to the PCH readout, but that's not rocket science either. It's
> >> just 21 callbacks to look at.
> >>
> > I like your suggestion, thanks!
> > it is what our user space needs from the kernel and with minimum kernel changes.
> > I will write it, test it and upload it with your permission (it is you
> > idea after all).
>
> You don't need permission. I made a suggestion and when you are doing the
> work I'm not in a position to veto posting it. We have an explicit tag
> for that 'Suggested-by:', which only says that someone suggested it to
> you, but then you went and implemented it, made sure it works etc.
>
> >> It might also require a new set of variant '3' IOTCLS to make that flag
> >> field work, but that's not going to make the change more complex and
> >> it's an exercise left to the experts of that IOCTL interface.
> >>
> > I think that I understand your meaning.
> > There is a backward compatibility problem here.
> >
> > Existing user space application using PTP_SYS_OFFSET_EXTENDED ioctl
> > won't have any problems because of the "extoff->rsv[0] ||
> > extoff->rsv[1] || extoff->rsv[2]" test, but what about all old user
> > space applications using: PTP_SYS_OFFSET ?
>
> So if there is a backwards compability issue with PTP_SYS_OFFSET2, then
> you need to introduce PTP_SYS_OFFSET3. The PTP_SYS_*2 variants were
> introduced to avoid backwards compatibility issues as well, but
> unfortunately that did not address the reserved fields problem for
> PTP_SYS_OFFSET2. PTP_SYS_OFFSET_EXTENDED2 should just work, but maybe
> the PTP maintainers want a full extension to '3'. Either way is fine.
>
https://patchwork.kernel.org/project/netdevbpf/patch/20240104212436.3276057-1-maheshb@google.com/

This was my attempt to solve a similar issue with the new ioctl op to
avoid backward compatibility issues.  Instead of flags I used the
clockid_t in a similar fashion.

Thanks,

> Thanks,
>
>         tglx
>
>