linux-kernel - Re: epoll handling in the alpha port

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Date:	Fri, 2 Feb 2007 06:48:28 +0100
From:	Willy Tarreau <w@....eu>
To:	Mike Frysinger <vapier@...too.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, rth@...ddle.net,
	linux-kernel@...r.kernel.org, alpha@...too.org
Subject: Re: epoll handling in the alpha port

On Fri, Feb 02, 2007 at 12:19:35AM -0500, Mike Frysinger wrote:
> On Friday 02 February 2007, Andrew Morton wrote:
> > It might be to late to fix this - we risk breaking userspace which worked
> > around it.
> 
> we'd be breaking userspace API, but not ABI ... and the largest consumers out 
> there (glibc/uclibc) have not been accounting for this, so we wouldnt be 
> breaking them
> 
> that's how we noticed the issue in Gentoo ... all the epoll calls are 
> automatically declared -ENOSYS stubs in glibc's libc.so
> 
> is there some other large consumer i'm not thinking of ?

Not necessarily some large consumers, but epoll() is quite older than its
kernel inclusion, so there certainly are some apps still using the syscall
without going through libc.

> > It would be safer to add the correct definitions while leaving the old ones
> > in place.
> 
> in the end, either works for me ... i can see linux's pretty hard 'dont break 
> userspace' policy coming into play here

I think it would be reasonable to use the NR_epoll* names first, and to
declare NR_sys_epoll* aliases which will point to NR_epoll*. You would
then add a comment with the date of the change, stating that you keep
them just in case there are some old apps. Then, someone coming on the
comment in 3 or 4 years could reasonably suggest removing those aliases.

Willy

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