Re: [dpdk-dev] [PATCH v4 2/2] ethdev: get the supported pools for a port

[Olivier MATZ <olivier.matz@6wind.com>]

On Fri, Sep 29, 2017 at 11:16:20AM +0100, santosh wrote:
> Hi Olivier,
> 
> 
> On Friday 29 September 2017 09:32 AM, Olivier MATZ wrote:
> > On Mon, Sep 25, 2017 at 10:52:31PM +0100, santosh wrote:
> >> Hi Olivier,
> >>
> >>
> >> On Monday 25 September 2017 08:37 AM, Olivier MATZ wrote:
> >>
> >>>> +{
> >>>> +	struct rte_eth_dev *dev;
> >>>> +	const char *tmp;
> >>>> +
> >>>> +	RTE_ETH_VALID_PORTID_OR_ERR_RET(port_id, -ENODEV);
> >>>> +
> >>>> +	if (pool == NULL)
> >>>> +		return -EINVAL;
> >>>> +
> >>>> +	dev = &rte_eth_devices[port_id];
> >>>> +
> >>>> +	if (*dev->dev_ops->pools_ops_supported == NULL) {
> >>>> +		tmp = rte_eal_mbuf_default_mempool_ops();
> >>>> +		if (!strcmp(tmp, pool))
> >>>> +			return 0;
> >>>> +		else
> >>>> +			return -ENOTSUP;
> >>> I don't understand why we are comparing with
> >>> rte_eal_mbuf_default_mempool_ops().
> >>>
> >>> It means that the result of the function would be influenced
> >>> by the parameter given by the user.
> >> But that will be only for ops not supported case and in that case,
> >> function _must_ make sure that if inputted param is _default_ops_name
> >> then function should return ops supported correct info (whether 
> >> returning '0' : Best ops or '1': ops does support 
> >> , this part is arguable.. meaning One can say that default_ops ='handle-name' is best possible handle Or 
> >> one of handle which platform supports).
> >>
> >>> I think that a PMD that does not implement ->pools_ops_supported
> >>> should always return 1 (mempool is supported).
> > I don't agree.
> > The result of this API (mempool ops supported or not by a PMD)
> > should not depend on what user asks for.
> >
> >> Return 1 says: PMD support this ops.. 
> >>
> >> So if ops is not supported and func returns with 1, then which ops application will use?
> >> If that ops is default_ops.. then How application will distinguish when to use default ops or
> >> param ops?.. as because in both cases func will return with value 1.
> >>
> >> The approach in the patch takes care of that condition and func will return -ENOTSUP 
> >> if (ops not support || inputted param not matching with default ops) otherwise will return
> >> 0 or 1.
> >>
> >> At application side; 
> >> For error case: In case of -ENOTSUP, its upto application to use _default_ops or exit.
> >> For good case: 0 or 1 case, func gaurantee that handle is either best handle for pool or pool supports
> >> that handle.. However in your suggestion if ops not supported case returns 1 then application is not 
> >> sure which ops to use.. default_ops Or input ops given to func.
> >>
> >> make sense? 
> > My proposition is:
> >
> > - what a PMD returns does not depend on used parameter:
> >   - 0: best support
> >   - 1: support
> >   - -ENOTSUP: not supported
> >
> > - if a PMD does not implement the _ops_supported() API, assume all pools
> >   are supported (returns 1)
> 
> If API returns 1 for PMD does not implement _ops_supported() case,
> then do we really need -ENOTSUP?

When the PMD explicitly does not support a mempool ops.

Not implementing the API means, like today: "I don't care what
the mempool ops is, so I a priori support all the ones available,
without preference".