linux-kernel - Re: [PATCH] char/tty_io: fix legacy pty name when more than 256 pty devices are requested

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Date:	Thu, 10 Sep 2009 13:35:52 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mauro Carvalho Chehab <mchehab@...radead.org>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Alan Cox <alan@...ux.intel.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Kay Sievers <kay.sievers@...y.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...e.de>
Subject: Re: [PATCH] char/tty_io: fix legacy pty name when more than 256 pty
 devices are requested

On 09/10/2009 01:05 PM, Mauro Carvalho Chehab wrote:
>>
>> Yes, but you have to port the application *anyway* do deal with the
>> namespace.
> 
> Or create some udev rules for that.
> 

udev rules does zero good, because the way the BSD ptys go, the
application itself needs to understand what the naming scheme is.  So it
is an application-by-application slog.

>> BSD tty allocation is done largely by each application,
>> which makes it even worse.  Furthermore, there is the static allocation
>> issue, so unless there is a concrete application which needs this *and*
>> cannot be ported to Unix98 ptys (which is the Right Thing[TM] to do) I
>> think Alan is right.
> 
> The amount of static allocation space can be controlled via pty.legacy_count
> boot parameter. It overrides whatever specified at CONFIG_LEGACY_PTY_COUNT.
> You can even let LEGACY_PTY_COUNT = 0 and enable the actual numbers of needed
> legacy ptys via boot parameter, where needed. So, this is not a problem on a
> real situation.

It still means you are statically allocating a fixed number at boot time.

	-hpa

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