linux-kernel - Re: [RFCv4] timerfd: add TFD_NOTIFY_CLOCK

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Message-ID: <AANLkTinZioShsr3O0Z=xaEQ-S=JBCgs_SS_LdsBnNhZ2@mail.gmail.com>
Date:	Thu, 10 Mar 2011 01:36:18 +0100
From:	Kay Sievers <kay.sievers@...y.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Alexander Shishkin <virtuoso@...nd.org>,
	linux-kernel@...r.kernel.org, Ken MacLeod <ken@...sko.slc.ut.us>,
	Shaun Reich <predator106@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Feng Tang <feng.tang@...el.com>,
	Michael Tokarev <mjt@....msk.ru>,
	Marcelo Tosatti <mtosatti@...hat.com>,
	John Stultz <johnstul@...ibm.com>,
	Chris Friesen <chris.friesen@...band.com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Artem Bityutskiy <dedekind1@...il.com>,
	Davide Libenzi <davidel@...ilserver.org>,
	linux-fsdevel@...r.kernel.org, linux-api@...r.kernel.org,
	Michael Kerrisk <mtk.manpages@...il.com>
Subject: Re: [RFCv4] timerfd: add TFD_NOTIFY_CLOCK_SET to watch for clock changes

On Thu, Mar 10, 2011 at 01:25, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Wed,  9 Mar 2011 16:36:51 +0200
> Alexander Shishkin <virtuoso@...nd.org> wrote:
>
>> Changes since v3:
>>  - changed timerfd_settime() semantics (see below)
>> Changes since v2:
>>  - replaced sysfs interface with a syscall
>>  - added sysctl/procfs handle to set a limit to the number of users
>>  - fixed issues pointed out by Greg.
>> Changes since v1:
>>  - updated against 2.6.36-rc1,
>>  - added notification/filtering options,
>>  - added Documentation/ABI/sysfs-kernel-time-notify interface description.

> It would be helpful to know if the identified users of this feature
> actually find it useful and adequate.  I guess the most common
> application is the 1,001 desktop clock widgets.  Do you have any
> feedback from any of the owners of those?

We want it for systemd, to provide cron-like functionality but without
the need to stupidly wake up every minute and check the system time
for possible jumps.

It also sounds useful for a generic resume (after system suspend)
notification for applications, which isn't really possible today.

Kay
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