linux-kernel - Re: [PATCH v5] posix timers: allocate timer id per process

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Date:	Tue, 23 Oct 2012 09:52:03 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stanislav Kinsbursky <skinsbursky@...allels.com>
Cc:	peterz@...radead.org, mingo@...hat.com, tglx@...utronix.de,
	devel@...nvz.org, linux-kernel@...r.kernel.org, xemul@...allels.com
Subject: Re: [PATCH v5] posix timers: allocate timer id per process

On Tue, 2012-10-23 at 11:40 +0400, Stanislav Kinsbursky wrote:
> This patch is required CRIU project (www.criu.org).
> To migrate processes with posix timers we have to make sure, that we can
> restore posix timer with proper id.
> Currently, this is not true, because timer ids are allocated globally.
> So, this is precursor patch and it's purpose is make posix timer id to be
> allocated per process.
> 
> Patch replaces global idr with global hash table for posix timers and
> makes timer ids unique not globally, but per process. Next free timer id is
> type of integer and stored on signal struct (posix_timer_id). If free timer id
> reaches negative value on timer creation, it will be dropped to zero and
> -EAGAIN will be returned to user.
> 
> Hash table has 512 slots.
> Key is constructed as follows:
> key = hash_32(hash_32(current->signal) ^ posix_timer_id));
> 
> Note: with this patch, id, returned to user, is not the minimal free
> amymore. It means, that id, returned to user space in loop, listed below, will
> be increasing on each iteration till INT_MAX and then dropped to zero:
> 
> while(1) {
> 	id = timer_create(...);
> 	timer_delete(id);
> }
> 
> Signed-off-by: Stanislav Kinsbursky <skinsbursky@...allels.com>
> 
> ---

SGTM

Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Thanks !


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