Re: [dpdk-dev] [PATCH] ethdev: reserve space in main structs for extension

[Thomas Monjalon <thomas@monjalon.net>]

08/11/2019 04:41, Stephen Hemminger:
> On Thu,  7 Nov 2019 23:15:24 +0100
> Thomas Monjalon <thomas@monjalon.net> wrote:
> 
> > The struct rte_eth_dev and rte_eth_dev_data are supposed
> > to be used internally only, but there is a chance that
> > increasing their size would break ABI for some applications.
> > In order to allow smooth addition of features without breaking
> > ABI compatibility, some space is reserved.
> > 
> > Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
> > ---
> > @@ -764,6 +767,9 @@ struct rte_eth_dev_data {
> > +
> > +	uint64_t reserved_64s[4]; /**< Reserved for future fields */
> > +	void *reserved_ptrs[4]; /**< Reserved for future fields */
> >  } __rte_cache_aligned;
> 
> Void * is 32 bits on 32 bit architectures is that helpful or not?

That's why I reserved separately uint and pointers.
If we need to add a pointer, we decrease the size of the pointer array
to keep the same struct size on all archs.