linux-kernel - Re: Issues with "x86, um: switch to generic fork/vfork/clone" commit

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Date:	Mon, 21 Jan 2013 02:30:11 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Nicolas Dichtel <nicolas.dichtel@...nd.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Issues with "x86, um: switch to generic fork/vfork/clone" commit

On Sun, Jan 20, 2013 at 05:40:28PM -0800, Linus Torvalds wrote:
> On Sun, Jan 20, 2013 at 5:22 PM, Al Viro <viro@...iv.linux.org.uk> wrote:
> >
> > Anyway, that's a separate story - semctl(2) is going to be ugly, no matter
> > what we do, but the rest of those guys doesn't have to.  How about the
> > following (completely untested):
> 
> Hmm.  Looks like the RightThing(tm) to me.
> 
> The thing that stands out that I question the value of that
> HAVE_SYSCALL_WRAPPERS thing. Is there any reason we don't just make
> all architectures use it? What's the downside? I'm not sure I see the
> point of the non-wrapper version.

Neither do I, to be honest.  It might be saving us a few cycles on
some architectures, but I'd like to see examples of that.  amd64
doesn't seem to be one, at least...

FWIW, there's another bit of ugliness around that area - all these
#define __SC_BLAH3, etc., all of the same form.  This stuff begs for
something like
#define __MAP1(m,t,a) m(t,a)
#define __MAP2(m,t,a,...) m(t,a) __MAP1(m,__VA_ARGS__)
#define __MAP3(m,t,a,...) m(t,a) __MAP2(m,__VA_ARGS__)
#define __MAP4(m,t,a,...) m(t,a) __MAP3(m,__VA_ARGS__)
#define __MAP5(m,t,a,...) m(t,a) __MAP4(m,__VA_ARGS__)
#define __MAP6(m,t,a,...) m(t,a) __MAP5(m,__VA_ARGS__)
#define __MAP(n,...) __MAP##n(__VA_ARGS__)
with __MAP(x,__SC_DECL,__VA_ARGS__) instead of __SC_DECL##x(__VA_ARGS__)
etc. in users...
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