linux-kernel - Re: [patch 3/3] timerfd: Implement write method

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20140522053101.GJ12819@moon>
Date:	Thu, 22 May 2014 09:31:01 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	linux-kernel@...r.kernel.org, shawn@...rchofgit.com,
	akpm@...ux-foundation.org, avagin@...nvz.org, xemul@...allels.com,
	vdavydov@...allels.com
Subject: Re: [patch 3/3] timerfd: Implement write method

On Thu, May 22, 2014 at 08:30:04AM +0900, Thomas Gleixner wrote:
> > 
> > > So what's the semantics of that write function? We really want to have
> > > that agreed on and documented in the man page.
> > 
> > The idea was to provide a way to setup @ticks into (nonzero) value
> > which we get from show_fdinfo output. Then when we restore it
> > we setup the timer and set @ticks to the value it had at dump
> > moment.
> 
> That's not describing the semantics. It's describing what you use it
> for.

That's I've been intending to use it for and as result the semantic
was to write unconditionally. But because I missed polling in first
place now I think such semantic is wrong and write() should be
a complete counterpart of read() method and wake up waiters.

> > > Right now the write will just update the ticks and nothing else. So
> > > what if there is a waiter already? What if there is a timer armed?
> > > 
> > > Can you please describe how checkpoint/restore is going to use all of
> > > this. How is the timer restored and how/when is the reader which was
> > > waiting in read/poll at the time of suspend reattached to it.
> > 
> > Thomas, I see what you mean. Need to think (I must admit I forgot about
> > polling of timerfds :( I were to restore timerfds like this
> > 
> >  - fetch data from fdinfo
> >  - use timer_create/settime to arm it
> >  - write @ticks then
> 
> That's clear to me.
> 
> So again you have to answer the questions:
> 
>    Do we just allow the write unconditionally?
>    Do we care about waking readers/pollers?
>  
> Whatever the answer is, it needs to be documented coherently in the
> changelog, in the code and in the man page.

"Yes" to both questions I think. Thomas I'll return with a new patchset,
testcase and man update.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/