linux-kernel - Re: [PATCH v2 17/31] ntsync: Allow waits to use the REALTIME clock.

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Message-ID: <3275980.aeNJFYEL58@camazotz>
Date: Wed, 21 Feb 2024 18:48:01 -0600
From: Elizabeth Figura <zfigura@...eweavers.com>
To: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 Jonathan Corbet <corbet@....net>, shuah <shuah@...nel.org>,
 Arnd Bergmann <arnd@...db.de>
Cc: linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
 wine-devel@...ehq.org,
 André Almeida <andrealmeid@...lia.com>,
 Wolfram Sang <wsa@...nel.org>, Arkadiusz Hiler <ahiler@...eweavers.com>,
 Peter Zijlstra <peterz@...radead.org>, Andy Lutomirski <luto@...nel.org>,
 linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
 Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v2 17/31] ntsync: Allow waits to use the REALTIME clock.

On Tuesday, 20 February 2024 01:01:59 CST Arnd Bergmann wrote:
> On Mon, Feb 19, 2024, at 23:38, Elizabeth Figura wrote:
> > NtWaitForMultipleObjects() can receive a timeout in two forms, relative or
> > absolute. Relative timeouts are unaffected by changes to the system time and do
> > not count down while the system suspends; for absolute timeouts the opposite is
> > true.
> >
> > In order to make the interface and implementation simpler, the ntsync driver
> > only deals in absolute timeouts. However, we need to be able to emulate both
> > behaviours apropos suspension and time adjustment, which is achieved by allowing
> > either the MONOTONIC or REALTIME clock to be used.
> >
> > Signed-off-by: Elizabeth Figura <zfigura@...eweavers.com>
> 
> I understand that there is no practical problem in building
> up the API one patch at a time in the initial merge, but
> it still feels wrong to have an incompatible ABI change in
> the middle of the series:
> 
> > @@ -35,6 +37,8 @@ struct ntsync_wait_args {
> >  	__u32 owner;
> >  	__u32 index;
> >  	__u32 alert;
> > +	__u32 flags;
> > +	__u32 pad;
> >  };
> 
> If this was patch to get merged at any later point, you'd have
> to support both the shorter and the longer structure layout
> with their distinct ioctl command codes.
> 
> If you do a v3 series, maybe just merge this patch into the
> one that introduces the struct ntsync_wait_args. Overall,
> you could probably have fewer but larger patches anyway
> without harming the review process, but other than this
> one that is not a problem.

Oops, yes, that does feel wrong now that you point it out.

I'll squash this in v3, assuming there's a need for one.

--Zeb