+ Ray for ABI
<snip>
>
> On Wed, Oct 28, 2020 at 02:28:43PM +0000, Akhil Goyal wrote:
> >
> > Hi Konstantin,
> >
> > > > > Hi Tech board members,
> > > > >
> > > > > I have a doubt about the ABI breakage in below addition of field.
> > > > > Could you please comment.
> > > > >
> > > > > > /** The data structure associated with each crypto device. */
> > > > > > struct rte_cryptodev {
> > > > > > dequeue_pkt_burst_t dequeue_burst; @@ -867,6 +922,10
> @@
> > > > > > struct rte_cryptodev {
> > > > > > __extension__
> > > > > > uint8_t attached : 1;
> > > > > > /**< Flag indicating the device is attached */
> > > > > > +
> > > > > > + struct rte_cryptodev_enq_cb_rcu *enq_cbs;
> > > > > > + /**< User application callback for pre enqueue processing */
> > > > > > +
> > > > > > } __rte_cache_aligned;
> > > > >
> > > > > Here rte_cryptodevs is defined in stable API list in map file
> > > > > which is a pointer To all rte_cryptodev and the above change is
> > > > > changing the size of the
> > > structure.
> > >
> > > While this patch adds new fields into rte_cryptodev structure, it
> > > doesn't change the size of it.
> > > struct rte_cryptodev is cache line aligned, so it's current size:
> > > 128B for 64-bit systems, and 64B(/128B) for 32-bit systems.
> > > So for 64-bit we have 47B implicitly reserved, and for 32-bit we
> > > have 19B reserved.
> > > That's enough to add two pointers without changing size of this struct.
> > >
> >
> > The structure is cache aligned, and if the cache line size in 32Byte
> > and the compilation is done on 64bit machine, then we will be left
> > with 15Bytes which is not sufficient for 2 pointers.
> > Do we have such systems? Am I missing something?
> >
>
> I don't think we support any such systems, so unless someone can point out
> a specific case where we need to support 32-byte CLs, I'd tend towards
> ignoring this as a non-issue.
Agree. I have not come across 32B cache line.
>
> > The reason I brought this into techboard is to have a consensus on
> > such change As rte_cryptodev is a very popular and stable structure.
> > Any changes to it may Have impacts which one person cannot judge all use
> cases.
> >
>
> Haven't been tracking this discussion much, but from what I read here, this
> doesn't look like an ABI break and should be ok.
If we are filling the holes in the cache line with new fields, it should not be
an ABI break.
>
> Regards,
> /Bruce
