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

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Message-ID: <20090910170538.3df10839@caramujo.chehab.org>
Date:	Thu, 10 Sep 2009 17:05:38 -0300
From:	Mauro Carvalho Chehab <mchehab@...radead.org>
To:	"H. Peter Anvin" <hpa@...or.com>
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

Em Thu, 10 Sep 2009 12:17:28 -0700
"H. Peter Anvin" <hpa@...or.com> escreveu:

> > In the case of the BSD sockets, the patch is not just an userless fix. This is
> > interesting when some applications are ported from other Unix'es and still uses BSD
> > pty's, since several other Unix flavors were defining a higher namespace size.
> > 
> > For example, on zOS Unix, a pty device seems to allow up to 10.000 pty numbers (in the
> > specific case of zOS Unix, they seem to be defined as /dev/[pt]typ[0-9]...) as shown at:
> > 	www.redbooks.ibm.com/redbooks/pdfs/sg245228.pdf
> > 
> 
> Yes, but you have to port the application *anyway* do deal with the
> namespace.

Or create some udev rules for that.

> 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.

Cheers,
Mauro
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