linux-kernel - Re: [PATCH] TTY: export NR_LDISC and N_* line discipline numbers to user-space

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Message-ID: <20110524133353.GB19488@suse.de>
Date:	Tue, 24 May 2011 06:33:53 -0700
From:	Greg KH <gregkh@...e.de>
To:	Florian Fainelli <ffainelli@...ebox.fr>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Maxime Bizon <mbizon@...ebox.fr>,
	Tilman Schmidt <tilman@...p.cc>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] TTY: export NR_LDISC and N_* line discipline numbers to
 user-space

On Tue, May 24, 2011 at 03:17:23PM +0200, Florian Fainelli wrote:
> Hello,
> 
> On Tuesday 24 May 2011 14:40:44 Greg KH wrote:
> > On Tue, May 24, 2011 at 10:43:03AM +0200, Florian Fainelli wrote:
> > > From: Florian Fainelli <ffainelli@...ebox.fr>
> > > 
> > > Since commit (4564f9e5: consolidate line discipline number definitions)
> > > the patch moved all line discipline number from a per-architecture
> > > termios.h to a shared one: tty.h. However, prior to this consolidation
> > > work, the line discipline numbers were outside of an ifdef
> > > __KERNEL__/endif block so these numbers used to be exported to
> > > user-space.
> > > 
> > > Since such numbers are kernel ABI anyway, and tty.h is already included
> > > for user- space header processing, just move these relevant defines
> > > outside of the ifdef __KERNEL__/endif block in include/linux/tty.h.
> > 
> > Any reason you didn't copy _any_ of the people who signed off on that
> > patch, or the original author of that patch?
> 
> No particular reason but my mistake, fixed that.
> 
> > 
> > Anyway, this is been this way for four years, since the 2.6.21 kernel
> > release.  Since no one has noticed, or complained, since then, how much
> > a problem is this really?
> 
> This is a problem because you may have out of tree drivers using a line 
> discpline number, and you do not want your companion user-space application to 
> have to use a different line discpline number but the one the kernel should 
> provide.
> 
> > 
> > Meaning, why has it taken this long for anyone to notice?
> 
> - long standing user-space applications such as pppd got their N_PPP long ago, 
> and do not have to worry about N_PPP being renumbered so they can just define 
> it in pppd's sources it won't break
> 
> - I started implementing a line discipline driver only a couple of months ago 
> and then realized that such ABI should have been exported

Ok, then it really isn't that important of a change :)

I'll queue it up for the next major merge window after this one, thanks.

greg k-h
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