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

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Message-ID: <20140521215707.GH12819@moon>
Date:	Thu, 22 May 2014 01:57:07 +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 06:43:08AM +0900, Thomas Gleixner wrote:
> On Tue, 29 Apr 2014, Cyrill Gorcunov wrote:
> > +static ssize_t timerfd_write(struct file *file, const char __user *buf,
> > +			     size_t count, loff_t *ppos)
> > +{
> > +	struct timerfd_ctx *ctx = file->private_data;
> > +	u64 ticks = 0;
> > +
> > +	if (count < sizeof(ticks))
> > +		return -EINVAL;
> > +
> > +	if (get_user(ticks, (u64 __user *) buf))
> > +		return -EFAULT;
> > +
> > +	spin_lock_irq(&ctx->wqh.lock);
> > +	ctx->ticks = ticks;
> 
> So what wakes a potential waiter in read/poll?

Why should it? You mean the scenario when timer is armed then
someone writes nonzero @ticks and we should wake waiters?
The idea was to setup this ticks on timer restore without
waking anyone. If it breaks the logic of timerfd in general,
then sure I need to rework. Hm?
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