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

["Luis R. Rodriguez" <mcgrof@xxxxxxxx>]

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

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