RE: [PATCH v2 1/3] eventdev/eth_rx: add params set/get APIs

["Naga Harish K, S V" <s.v.naga.harish.k@intel.com>]

> -----Original Message-----
> From: Jerin Jacob <jerinjacobk@gmail.com>
> Sent: Saturday, January 28, 2023 4:24 PM
> To: Naga Harish K, S V <s.v.naga.harish.k@intel.com>
> Cc: jerinj@marvell.com; Carrillo, Erik G <erik.g.carrillo@intel.com>; Gujjar,
> Abhinandan S <abhinandan.gujjar@intel.com>; dev@dpdk.org;
> Jayatheerthan, Jay <jay.jayatheerthan@intel.com>
> Subject: Re: [PATCH v2 1/3] eventdev/eth_rx: add params set/get APIs
> 
> On Wed, Jan 25, 2023 at 10:02 PM Naga Harish K, S V
> <s.v.naga.harish.k@intel.com> wrote:
> >
> >
> >
> > > -----Original Message-----
> > > From: Jerin Jacob <jerinjacobk@gmail.com>
> 
> > > > > >
> > > > > > > > +        */
> > > > > > > > +       uint32_t rsvd[15];
> > > > > > > > +       /**< Reserved fields for future use */
> > > > > > >
> > > > > > > Introduce rte_event_eth_rx_adapter_runtime_params_init() to
> > > make
> > > > > > > sure rsvd is zero.
> > > > > > >
> > > > > >
> > > > > > The reserved fields are not used by the adapter or application.
> > > > > > Not sure Is it necessary to Introduce a new API to clear reserved
> fields.
> > > > >
> > > > > When adapter starts using new fileds(when we add new fieds in
> > > > > future), the old applicaiton which is not using
> > > > > rte_event_eth_rx_adapter_runtime_params_init() may have junk
> > > > > value and then adapter implementation will behave bad.
> > > > >
> > > > >
> > > >
> > > > does it mean, the application doesn't re-compile for the new DPDK?
> > >
> > > Yes. No need recompile if ABI not breaking.
> > >
> > > > When some of the reserved fields are used in the future, the
> > > > application
> > > also may need to be recompiled along with DPDK right?
> > > > As the application also may need to use the newly consumed
> > > > reserved
> > > fields?
> > >
> > > The problematic case is:
> > >
> > > Adapter implementation of 23.07(Assuming there is change params)
> > > field needs to work with application of 23.03.
> > > rte_event_eth_rx_adapter_runtime_params_init() will sove that.
> > >
> >
> > As rte_event_eth_rx_adapter_runtime_params_init() initializes only
> reserved fields to zero,  it may not solve the issue in this case.
> 
> rte_event_eth_rx_adapter_runtime_params_init() needs to zero all fields,
> not just reserved field.
> The application calling sequence  is
> 
> struct my_config c;
> rte_event_eth_rx_adapter_runtime_params_init(&c)
> c.interseted_filed_to_be_updated = val;
> 
Can it be done like 
	struct my_config c = {0};
	c.interseted_filed_to_be_updated = val;
and update Doxygen comments to recommend above usage to reset all fields?
This way,  rte_event_eth_rx_adapter_runtime_params_init() can be avoided.

> Let me share an example and you can tell where is the issue
> 
> 1)Assume parameter structure is 64B and for 22.03 8B are used.
> 2)rte_event_eth_rx_adapter_runtime_params_init() will clear all 64B.
> 3)There is an application written based on 22.03 which using only 8B after
> calling rte_event_eth_rx_adapter_runtime_params_init()
> 4)Assume, in 22.07 another 8B added to structure.
> 5)Now, the application (3) needs to run on 22.07. Since the application is
> calling rte_event_eth_rx_adapter_runtime_params_init()
> and 9 to 15B are zero, the implementation will not go bad.
> 
> > The old application only tries to set/get previous valid fields and the newly
> used fields may still contain junk value.
> > If the application wants to make use of any the newly used params, the
> application changes are required anyway.
> 
> Yes. If application wants to make use of newly added features. No need to
> change if new features are not needed for old application.