Re: [PATCH v4 1/3] lib: introduce dispatcher library

[Bruce Richardson <bruce.richardson@intel.com>]

On Tue, Sep 26, 2023 at 11:58:37PM +0530, Jerin Jacob wrote:
> On Mon, Sep 25, 2023 at 12:41 PM Mattias Rönnblom <hofors@lysator.liu.se> wrote:
> >
> > On 2023-09-22 09:38, Mattias Rönnblom wrote:
> >
> > <snip>
> >
> > > +int
> > > +rte_dispatcher_create(uint8_t id, uint8_t event_dev_id)
> > > +{
> >
> >
> > There are two changes I'm considering:
> >
> > 1) Removing the "id" to identify the dispatcher, replacing it with an
> > forward-declared rte_dispatcher struct pointer.
> >
> > struct rte_dispatcher;
> >
> > struct rte_dispatcher *
> > rte_dispatcher_create(uint8_t event_dev_id);
> >
> >
> > The original reason for using an integer id to identify a dispatcher is
> > to make it look like everything else in Eventdev. I find this pattern a
> > little awkward to use - in particular the fact the id is
> > application-allocated (and thus require coordination between different
> > part of the application in case multiple instances are used).
> >
> > 2) Adding a flags field to the create function "for future use". But
> > since the API is experimental, there may not be that much need to
> > attempt to be future-proof?
> >
> > Any thoughts are appreciated.
> 
> IMO, better to have rte_dispatcher_create(struct
> rte_dispatch_create_params *params)
> for better future proofing with specific
> rte_dispatch_crearte_params_init() API(No need to add reserved fields
> in rte_dispatch_create_params  now, may need only for before removing
> experimental status)
> 
> Just 2c.
> 

I don't like using structs in those cases, I'd much rather have a flags
parameter, as flags can be checked for explicit zeros for future proofing,
while a struct cannot be checked for extra space on the end for future
fields added.

Furthermore, if we need to add new parameters to the create function, I
actually believe it is better to add them as explicit parameters rather
than new fields to the struct. Struct fields can be missed by a user just
recompiling, while new function parameters will be flagged by the compiler
to make the user aware of the change. [There would be no change for ABI
compatibility as function versioning would be usable in both cases]

/Bruce