linux-kernel - Re: [RFC PATCH 6/9] livepatch: create per-task consistency model

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Message-ID: <20150218131526.GB8611@treble.redhat.com>
Date:	Wed, 18 Feb 2015 07:15:26 -0600
From:	Josh Poimboeuf <jpoimboe@...hat.com>
To:	Miroslav Benes <mbenes@...e.cz>
Cc:	Seth Jennings <sjenning@...hat.com>, Jiri Kosina <jkosina@...e.cz>,
	Vojtech Pavlik <vojtech@...e.cz>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	live-patching@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 6/9] livepatch: create per-task consistency model

On Wed, Feb 18, 2015 at 01:42:56PM +0100, Miroslav Benes wrote:
> On Tue, 17 Feb 2015, Josh Poimboeuf wrote:
> 
> > On Tue, Feb 17, 2015 at 04:48:39PM +0100, Miroslav Benes wrote:
> > > On Tue, 17 Feb 2015, Josh Poimboeuf wrote:
> > > 
> > > > On Mon, Feb 16, 2015 at 03:19:10PM +0100, Miroslav Benes wrote:
> > 
> > > > > and externs for functions are redundant.
> > > > 
> > > > I agree, but it seems to be the norm in Linux.  I have no idea why.  I'm
> > > > just following the existing convention.
> > > 
> > > Yes, I know. It seems that each author does it differently. You can find 
> > > both forms even in one header file in the kernel. There is no functional 
> > > difference AFAIK (it is not the case for variables of course). So as long 
> > > as we are consistent I do not care. And since we have externs already in 
> > > livepatch.h... you can scratch this remark if you want to :)
> > 
> > Ok.  If there are no objections, let's stick with our existing
> > nonsensical convention for now :-)
> 
> So I was thinking about it again and we should not use bad patterns in our 
> code from the beginning. Externs do not make sense so let's get rid of 
> them everywhere (i.e. in the consistency model and also in livepatch.h). 
> 
> The C specification talks about extern in context of internal and external 
> linkages or in context of inline functions but it does not make any sense 
> to me. Could you look at the specification and tell me if it makes any 
> sense to you, please?

Relevant parts from C11:

	For an identifier declared with the storage-class specifier extern in a
	scope in which a prior declaration of that identifier is visible, if the
	prior declaration specifies internal or external linkage, the linkage of
	the identifier at the later declaration is the same as the linkage
	specified at the prior declaration.  If no prior declaration is visible,
	or if the prior declaration specifies no linkage, then the identifier
	has external linkage.

	If the declaration of an identifier for a function has no storage-class
	specifier, its linkage is determined exactly as if it were declared with
	the storage-class specifier extern .If the declaration of an identifier
	for an object has file scope and no storage-class specifier, its linkage
	is external.

Sounds to me like "extern" is redundant for functions.  I'm fine with
removing it.  Care to work up a patch for livepatch.h?

> 
> Jiri, Vojtech, do you have any opinion about this?
> 
> Miroslav

-- 
Josh
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