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

Miroslav Benes
2015-02-18T13:42:10Z

On Wed, 18 Feb 2015, Josh Poimboeuf wrote:

> 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?

Agreed. I'll do that. Thanks.

Miroslav