Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932637AbaFJUFp (ORCPT ); Tue, 10 Jun 2014 16:05:45 -0400 Received: from mail-ve0-f173.google.com ([209.85.128.173]:36434 "EHLO mail-ve0-f173.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753361AbaFJUFn (ORCPT ); Tue, 10 Jun 2014 16:05:43 -0400 MIME-Version: 1.0 In-Reply-To: References: <20140428212517.200264067@openvz.org> <20140428213301.507657833@openvz.org> <20140610163530.GF2243@moon> From: Andy Lutomirski Date: Tue, 10 Jun 2014 13:05:22 -0700 Message-ID: Subject: Re: [patch 3/3] timerfd: Implement write method To: Michael Kerrisk-manpages Cc: Cyrill Gorcunov , Thomas Gleixner , LKML , Andrew Morton , Andrey Vagin , Pavel Emelyanov , vdavydov@parallels.com, Linux API Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Jun 10, 2014 at 1:03 PM, Michael Kerrisk (man-pages) wrote: > [CC += linux-api@] > > On Tue, Jun 10, 2014 at 6:35 PM, Cyrill Gorcunov wrote: >> On Thu, May 22, 2014 at 06:58:19AM +0900, Thomas Gleixner wrote: >>> > >>> > So what wakes a potential waiter in read/poll? >>> >>> And who is updating timerfd_create(2) ? >> >> Thomas, could you please take a look if the approach below is acceptable? >> If it will be fine I update manpage then. >> --- >> From: Cyrill Gorcunov >> Subject: timerfd: Implement timerfd_ioctl method to restore timerfd_ctx::ticks >> >> The read() of timerfd files allows to fetch the number of timer ticks >> while there is no way to set it back from userspace. >> >> To restore the timer's state as it was at checkpoint moment we need >> a path to bring @ticks back. Initially I thought about writing ticks >> back via write() interface but it seems such API is somehow obscure. >> >> Instead implement timerfd_ioctl() method with TFD_IOC_SET_TICKS >> command which requires CAP_SYS_RESOURCE capability to be able to >> set @ticks into arbitrary value. Note this command doesn't wake >> up readers/waiters and its purpose only to serve C/R needs >> (for same sake I wrapped code with CONFIG_CHECKPOINT_RESTORE). >> Still if needed the ioctl may be extended for new commands >> and CONFIG_CHECKPOINT_RESTORE dropped off. Why does this need CAP_SYS_RESOURCE? --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/