linux-kernel - Re: [PATCHv6 0/7] system time changes notification

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Date:	Wed, 17 Nov 2010 23:29:13 +0200
From:	Alexander Shishkin <virtuoso@...nd.org>
To:	Davide Libenzi <davidel@...ilserver.org>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Kyle Moffett <kyle@...fetthome.net>, Valdis.Kletnieks@...edu,
	LKML <linux-kernel@...r.kernel.org>,
	John Stultz <johnstul@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Kay Sievers <kay.sievers@...y.org>, Greg KH <gregkh@...e.de>,
	Chris Friesen <chris.friesen@...band.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Alexander Shishkin <virtuoso@...nd.org>
Subject: Re: [PATCHv6 0/7] system time changes notification

On Wed, Nov 17, 2010 at 12:42:52PM -0800, Davide Libenzi wrote:
> On Wed, 17 Nov 2010, Alexander Shishkin wrote:
> 
> > > But what you folks really want for this stuff is an extension to
> > > timerfd as you want to be able to poll, right?
> > > 
> > > So what about the following:
> > > 
> > > Add a new flag TDF_NOTIFY_CLOCK_WAS_SET to the timerfd flags. Now this
> > > flag adds the timer to a separate list, which gets woken up when the
> > > clock is set.
> > > 
> > > No new syscall, just a few lines of code in fs/timerfd.c and
> > > clock_was_set().
> > > 
> > > Thoughts ?
> > 
> > Something like this (sans ugliness)?
> 
> Oh, gosh, please.  This is interface-multiplexing-a-palooza.

Thomas made a suggestion, I came up with how it might look like so that
pros and cons are clearer to everyone (or at least me) and can be discussed
on technical grounds. Code talks, sort of. I'm not convinced that a timer
that returns to userspace when the clock changes is such a bad idea, could
you please elaborate?

> It should be decided if the feature makes sense, and then have proper 
> interface, instead of multiplexing unrelated insterfaces.

It is not a question any more.

> This is a sort of system-event-report pattern.  What is wrong with using a 
> netlink-based transport for those kind of things?

What is wrong with eventfd-based implementation that's already there?

Thanks,
--
Alex
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