Re: [PATCH v2 net-next 1/2] net: dsa: lan9303: Add port_fast_age and port_fdb_dump methods

[Egil Hjelmeland]

On 19. okt. 2017 17:15, David Laight wrote:
> From: Andrew Lunn
> > Sent: 19 October 2017 15:15
> > > > +/* Clear learned (non-static) entry on given port */
> > > > +static void alr_loop_cb_del_port_learned(struct lan9303 *chip, u32 dat0,
> > > > +					 u32 dat1, int portmap, void *ctx)
> > > > +{
> > > > +	int *port = ctx;
> > >
> > > You can get the value directly to make the line below more readable:
> > >
> > >      int port = *(int *)ctx;
> >
> > You have to be a bit careful with this. You often see people
> > submitting patches taking away casts for void * pointers.
> > If they do that here, it should at least not compile...
> >
> > So maybe do it in two steps?
> >
> >     int * pport = ctx;
> >     int port = *pport;
>
> IMHO it is best to define a struct for the 'ctx and then do:
> 	..., void *v_ctx)
> {
> 	foo_ctx *ctx = v_ctx;
> 	int port = ctx->port;
>
> That stops anyone having to double-check that the *(int *)
> is operating on a pointer to an integer of the correct size.

Does casting to a struct pointer require less manual double-check than
to a int-pointer? In neither cases the compiler can protect us, IFAIK.
But on the other hand, a the text "foo_ctx" can searched in the editor.
So in that respect it can somewhat aid to the double-checking.

So I can do that.


> One of the syntax checkers probably ought to generate a warning
> for *(integer_type *)foo since it is often a bug.
>
> 	David

Egil