Re: [dpdk-dev] [PATCH] ethdev: fix setting of MAC address

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

Hi,

On Mon, Dec 18, 2017 at 02:38:55PM +0300, Andrew Rybchenko wrote:
> On 12/18/2017 01:53 PM, Igor Ryzhov wrote:
> > 
> > On Mon, Dec 18, 2017 at 1:35 PM, Andrew Rybchenko
> > <arybchenko@solarflare.com <mailto:arybchenko@solarflare.com>> wrote:
> > 
> >     On 12/14/2017 08:15 PM, Olivier Matz wrote:
> > 
> >         From: Laurent Hardy <laurent.hardy@6wind.com
> >         <mailto:laurent.hardy@6wind.com>>
> > 
> >         When a new mac address is set, it is saved in dev->data->mac_addrs
> >         before the ethdev handler is called.
> > 
> >         First, it is inconsistent with the other ethdev functions
> >         rte_eth_dev_mac_addr_remove() and rte_eth_dev_mac_addr_add().
> > 
> >         Moreover, it prevents the drivers from wrongly comparing the
> >         old address
> >         and the new one, like it's done in i40evf driver:
> > 
> >                 if (is_same_ether_addr(mac_addr, dev->data->mac_addrs))
> >                         return;
> > 
> >         Fixes: 943c2d899a0c ("net/i40e: set VF MAC from VF")
> >         Fixes: 854d8ad4ef68 ("ethdev: add default mac address modifier")
> >         Cc: stable@dpdk.org <mailto:stable@dpdk.org>
> > 
> >         Signed-off-by: Laurent Hardy <laurent.hardy@6wind.com
> >         <mailto:laurent.hardy@6wind.com>>
> >         ---
> >           lib/librte_ether/rte_ethdev.c | 4 ++--
> >           1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> >         diff --git a/lib/librte_ether/rte_ethdev.c
> >         b/lib/librte_ether/rte_ethdev.c
> >         index 4f492e3db..297c02a54 100644
> >         --- a/lib/librte_ether/rte_ethdev.c
> >         +++ b/lib/librte_ether/rte_ethdev.c
> >         @@ -2643,11 +2643,11 @@
> >         rte_eth_dev_default_mac_addr_set(uint16_t port_id, struct
> >         ether_addr *addr)
> >                 dev = &rte_eth_devices[port_id];
> >                 RTE_FUNC_PTR_OR_ERR_RET(*dev->dev_ops->mac_addr_set,
> >         -ENOTSUP);
> >           +     (*dev->dev_ops->mac_addr_set)(dev, addr);
> >         +
> >                 /* Update default address in NIC data structure */
> >                 ether_addr_copy(addr, &dev->data->mac_addrs[0]);
> >           -     (*dev->dev_ops->mac_addr_set)(dev, addr);
> >         -
> >                 return 0;
> >           }
> > 
> > 
> >     NACK, unfortunately it will break net/sfc in one of branches when
> >     a new MAC
> >     is set using restart. It relies on the fact that a new MAC is
> >     already available in
> >     device data.
> > 
> > 
> > Hello Andrew,
> >
> > Don't you think that it's not correct that net/sfc works that way?
> >
> > If we go further, dev->dev_ops->mac_addr_set not only should be called
> before ether_addr_copy.
> > It should  return status code, and in case of error ether_addr_copy
> > shouldn't be
> called at all.
> > Am I wrong?

Yes, I also have the same feeling.

> Current behaviour is convenient. Alternative will require copy of MAC
> address
> to set in device private data and one more copy in the function to rollback
> in
> the case of failure. If there are good reasons to change behaviour, I don't
> mind but PMDs should be reviewed carefully and fixed before the change.

Right. The first version of the patch was just a fix of the i40e code,
which was of course less risky. But we finally decided to to that way
for consistency.

I will review the other PMDs and send a v2 that should not break
them. If you have any guidelines for net/sfc, they will be welcome :)

Thanks for the review.
Olivier