netdev - Re: [PATCH 1/2] avoid OPEN_MAX in SCM_MAX

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Date:	Tue, 13 Mar 2007 17:55:08 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Benjamin LaHaise <bcrl@...ck.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] avoid OPEN_MAX in SCM_MAX_FD

> I'd actually prefer this as part of the "remove OPEN_MAX" patch.

Ok.  (But now you're going to argue with me about "remove OPEN_MAX",
and you haven't said you have any problem with changing SCM_MAX_FD,
so why make it wait?)

> That said, it actually worries me that you should call "_SC_OPEN_MAX". 
[...]
> For example, I know perfectly well that I should use _SC_PATH_MAX, but a 
> *lot* of code simply doesn't care. In git, I used PATH_MAX, and the reason 
[...]

Ok, fine.  But PATH_MAX is a real constant that has some meaning in the
kernel.  It's perfectly correct to use PATH_MAX as a constant on a system
like Linux that defines it and means what it says.  Conversely, OPEN_MAX
has no useful relationship with anything the kernel is doing at all.

> So, what's the likelihood that this will break some old programs? I 
> realize that modern distributions don't put the kernel headers in their 
> user-visible includes any more, but the breakage is most likely exactly 
> for old programs and older distributions.

Well, I don't know for sure.  It doesn't seem all that likely to me (not
like PATH_MAX), as there has been getdtablesize() since before there was
OPEN_MAX by that name (not to mention before there was Linux).  If things
use OPEN_MAX as a constant for arrays, they're already broken unless they
call setrlimit to constrain themselves.  Getting things fixed has to start
somewhere.

Thanks,
Roland

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