linux-kernel - Re: [RFC v2 2/7] tables.h: add linker table support

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Date:	Fri, 19 Feb 2016 22:12:10 +0100
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Luis R. Rodriguez" <mcgrof@...nel.org>, tglx@...utronix.de,
	mingo@...hat.com, bp@...en8.de, x86@...nel.org,
	linux-kernel@...r.kernel.org, luto@...capital.net,
	boris.ostrovsky@...cle.com, rusty@...tcorp.com.au,
	david.vrabel@...rix.com, konrad.wilk@...cle.com, mcb30@...e.org,
	jgross@...e.com, ming.lei@...onical.com,
	gregkh@...uxfoundation.org, arnd@...db.de,
	linux-arch@...r.kernel.org, linux@....linux.org.uk,
	benh@...nel.crashing.org, jbaron@...mai.com, ananth@...ibm.com,
	anil.s.keshavamurthy@...el.com, davem@...emloft.net,
	masami.hiramatsu.pt@...achi.com, andriy.shevchenko@...ux.intel.com,
	dwmw2@...radead.org, xen-devel@...ts.xensource.com
Subject: Re: [RFC v2 2/7] tables.h: add linker table support

On Fri, Feb 19, 2016 at 12:33:27PM -0800, H. Peter Anvin wrote:
> On 02/19/2016 05:45 AM, Luis R. Rodriguez wrote:
> > +/**
> > + * LINKTABLE_RUN_ERR - run each linker table entry func and return error if any
> > + *
> > + * @tbl: linker table
> > + * @func: structure name for the function name we want to call.
> > + * @args...: arguments to pass to func
> > + *
> > + * Example usage:
> > + *
> > + *   unsigned int err = LINKTABLE_RUN_ERR(frobnicator_fns, some_run,);
> > + */
> > +#define LINKTABLE_RUN_ERR(tbl, func, args...)				\
> > +({									\
> > +	size_t i;							\
> > +	int err = 0;							\
> > +	for (i = 0; !err && i < LINKTABLE_SIZE(tbl); i++)		\
> > +		err = (tbl[i]).func (args);				\
> > +		err; \
> > +})
> 
> This is wrong and pointless.  As written it returns the error code of
> the last instance.
> 
> What I suggested for this macro was that we ought to exit the loop on error.
> 
> Furthermore:
> 
> 1. Using an advancing pointer would make more sense than a counter.

OK I'll modify to use LINKTABLE_FOR_EACH and much cleaner and obvious
code to bail on error.

> 2. .func doesn't make any sense -- it ought to be "func"; otherwise you
>     can't call into either a table containing pure function pointers,
>     nor into a field of table *pointed to* by the table; which is
>     likely to be quite common.
> 
>     So the idea is to use something like:
> 
>     /* Array of function pointers */
>     LINKTABLE_RUN_ALL(frobnicator_fns, , arg1, arg2);
> 
>     /* Array of structures */
>     LINKTABLE_RUN_ALL(frobnicator_fns, .some_run, arg1, arg2);
> 
>     /* Array of structure pointers */
>     LINKTABLE_RUN_ALL(frobnicator_fns, ->some_run, arg1, arg2);

Ah that's sexy, thanks. Will amend.

  Luis