Re: [PATCH 06/13] null: fake PMD capabilities

[Michal Miroslaw <mirq-linux@rere.qmqm.pl>]

On Tue, Dec 13, 2016 at 02:37:34PM +0000, Ananyev, Konstantin wrote:
> 
> 
> > -----Original Message-----
> > From: Michal Miroslaw [mailto:mirq-linux@rere.qmqm.pl]
> > Sent: Tuesday, December 13, 2016 2:27 PM
> > To: Ananyev, Konstantin <konstantin.ananyev@intel.com>
> > Cc: dev@dpdk.org
> > Subject: Re: [dpdk-dev] [PATCH 06/13] null: fake PMD capabilities
> > 
> > On Tue, Dec 13, 2016 at 10:48:32AM +0000, Ananyev, Konstantin wrote:
> > > > -----Original Message-----
> > > > From: dev [mailto:dev-bounces@dpdk.org] On Behalf Of Michal Miroslaw
> > > > Sent: Tuesday, December 13, 2016 1:08 AM
> > > > To: dev@dpdk.org
> > > > Subject: [dpdk-dev] [PATCH 06/13] null: fake PMD capabilities
> > > >
> > > > From: Paweł Małachowski <pawel.malachowski@atendesoftware.pl>
> > > >
> > > > Thanks to that change we can use Null PMD for testing purposes.
> > > >
> > > > Signed-off-by: Michał Mirosław <michal.miroslaw@atendesoftware.pl>
> > > > ---
> > > >  drivers/net/null/rte_eth_null.c | 13 ++++++++++++-
> > > >  1 file changed, 12 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/net/null/rte_eth_null.c b/drivers/net/null/rte_eth_null.c
> > > > index 836d982..f32ba2a 100644
> > > > --- a/drivers/net/null/rte_eth_null.c
> > > > +++ b/drivers/net/null/rte_eth_null.c
> > > > @@ -284,6 +284,9 @@ eth_tx_queue_setup(struct rte_eth_dev *dev, uint16_t tx_queue_id,
> > > >  	return 0;
> > > >  }
> > > >
> > > > +static void
> > > > +eth_dev_void_ok(struct rte_eth_dev *dev __rte_unused) { return; }
> > > > +
> > > >
> > > >  static void
> > > >  eth_dev_info(struct rte_eth_dev *dev,
> > > > @@ -304,6 +307,9 @@ eth_dev_info(struct rte_eth_dev *dev,
> > > >  	dev_info->pci_dev = NULL;
> > > >  	dev_info->reta_size = internals->reta_size;
> > > >  	dev_info->flow_type_rss_offloads = internals->flow_type_rss_offloads;
> > > > +	/* We hereby declare we can RX-offload VLAN-s out of thin air and update checksums and VLANs before sinking packets in
> > > > /dev/null */
> > > > +	dev_info->rx_offload_capa = DEV_RX_OFFLOAD_VLAN_STRIP;
> > > > +	dev_info->tx_offload_capa = DEV_TX_OFFLOAD_VLAN_INSERT | DEV_TX_OFFLOAD_IPV4_CKSUM;
> > >
> > > Hmm, how could it be supported if all that null PMD does on TX - just free the packets?
> > > Same question for RX.
> > 
> > You could imagine, that before dropping the packet you insert the tag
> > and calculate the checksum. The observed effect will be the same.
> > 
> > On RX this always indicates lack of VLAN tag. So whether the offload
> > is enabled or not it doesn't matter.
> 
> Of course user can imagine whatever he likes, but what the point to advertise these capabilities,
> when the PMD clearly doesn't have them?
> Again, why these particular ones?

Hmm. I guess we can expand the set. Those were the ones we actually use
(depend on) for testing our code.

This allows to use null PMD for testing in place of real network interface
with those offloads. This patch is to keep users from having to place if's
around their code just to support test scenarios with null PMD.

Best Regards,
Michał Mirosław