linux-kernel - Re: [RFC PATCH 5/9] ntsync: Introduce NTSYNC_IOC_WAIT

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Date: Wed, 24 Jan 2024 20:52:52 +0100
From: "Arnd Bergmann" <arnd@...db.de>
To: "Elizabeth Figura" <zfigura@...eweavers.com>,
 "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
 linux-kernel@...r.kernel.org, linux-api@...r.kernel.org
Cc: wine-devel@...ehq.org,
 André Almeida <andrealmeid@...lia.com>,
 "Wolfram Sang" <wsa@...nel.org>, "Arkadiusz Hiler" <ahiler@...eweavers.com>,
 "Peter Zijlstra" <peterz@...radead.org>
Subject: Re: [RFC PATCH 5/9] ntsync: Introduce NTSYNC_IOC_WAIT_ANY.

On Wed, Jan 24, 2024, at 19:02, Elizabeth Figura wrote:
> On Wednesday, 24 January 2024 01:56:52 CST Arnd Bergmann wrote:
>> On Wed, Jan 24, 2024, at 01:40, Elizabeth Figura wrote:
>> 
>> > +	if (args->timeout) {
>> > +		struct timespec64 to;
>> > +
>> > +		if (get_timespec64(&to, u64_to_user_ptr(args->timeout)))
>> > +			return -EFAULT;
>> > +		if (!timespec64_valid(&to))
>> > +			return -EINVAL;
>> > +
>> > +		timeout = timespec64_to_ns(&to);
>> > +	}
>> 
>> Have you considered just passing the nanosecond value here?
>> Since you do not appear to write it back, that would avoid
>> the complexities of dealing with timespec layout differences
>> and indirection.
>
> That'd be nicer in general. I think there was some documentation that advised
> using timespec64 for new ioctl interfaces but it may have been outdated or
> misread.

It's probably something I wrote. It depends a bit on
whether you have an absolute or relative timeout. If
the timeout is relative to the current time as I understand
it is here, a 64-bit number seems more logical to me.

For absolute times, I would usually use a __kernel_timespec,
especially if it's CLOCK_REALTIME. In this case you would
also need to specify the time domain.

      Arnd