linux-kernel - Re: [PATCH 2/2] tty: rework pty count limiting

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Message-ID: <20120102172903.GB19782@suse.de>
Date:	Mon, 2 Jan 2012 09:29:03 -0800
From:	Greg KH <gregkh@...e.de>
To:	Konstantin Khlebnikov <khlebnikov@...nvz.org>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] tty: rework pty count limiting

On Mon, Jan 02, 2012 at 09:23:01PM +0400, Konstantin Khlebnikov wrote:
> After adding devpts multiple-insrances sysctl kernel.pty.max limit pty count for
> each devpts instance independently, while kernel.pty.nr shows total pty count.
> 
> This patch restores sysctl kernel.pty.max as global limit (4096 by default),
> adds pty reseve for main devpts (mounted without "newinstance" argument),
> and new sysctl to tune it: kernel.pty.reserve (1024 by default)
> 
> Also it adds devpts mount option "max=%d" to limit pty count for each devpts
> instance independently. (by default NR_UNIX98_PTY_MAX == 2^20)
> 
> Thus devpts instances in containers cannot eat up all available pty even if we didn't
> set any limits, while with "max" argument we can adjust limits more precisely.
> 
> Plus, now open("/dev/ptmx") return -ENOSPC in case lack of pty indexes,
> this is more informative than -EIO.

That's a userspace api change, why is this going to be allowed?

greg k-h
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