RE: [PATCH v3 0/5] Introduce variable length mdev alias

Parav Pandit
2019-09-11T16:40:38Z

> -----Original Message-----
> From: linux-kernel-owner@vger.kernel.org <linux-kernel-
> owner@vger.kernel.org> On Behalf Of Parav Pandit
> Sent: Wednesday, September 11, 2019 10:31 AM
> To: Alex Williamson <alex.williamson@redhat.com>
> Cc: Jiri Pirko <jiri@mellanox.com>; kwankhede@nvidia.com;
> cohuck@redhat.com; davem@davemloft.net; kvm@vger.kernel.org; linux-
> kernel@vger.kernel.org; netdev@vger.kernel.org
> Subject: RE: [PATCH v3 0/5] Introduce variable length mdev alias
>
> Hi Alex,
>
> > -----Original Message-----
> > From: Alex Williamson <alex.williamson@redhat.com>
> > Sent: Wednesday, September 11, 2019 8:56 AM
> > To: Parav Pandit <parav@mellanox.com>
> > Cc: Jiri Pirko <jiri@mellanox.com>; kwankhede@nvidia.com;
> > cohuck@redhat.com; davem@davemloft.net; kvm@vger.kernel.org; linux-
> > kernel@vger.kernel.org; netdev@vger.kernel.org
> > Subject: Re: [PATCH v3 0/5] Introduce variable length mdev alias
> >
> > On Mon, 9 Sep 2019 20:42:32 +0000
> > Parav Pandit <parav@mellanox.com> wrote:
> >
> > > Hi Alex,
> > >
> > > > -----Original Message-----
> > > > From: Parav Pandit <parav@mellanox.com>
> > > > Sent: Sunday, September 1, 2019 11:25 PM
> > > > To: alex.williamson@redhat.com; Jiri Pirko <jiri@mellanox.com>;
> > > > kwankhede@nvidia.com; cohuck@redhat.com; davem@davemloft.net
> > > > Cc: kvm@vger.kernel.org; linux-kernel@vger.kernel.org;
> > > > netdev@vger.kernel.org; Parav Pandit <parav@mellanox.com>
> > > > Subject: [PATCH v3 0/5] Introduce variable length mdev alias
> > > >
> > > > To have consistent naming for the netdevice of a mdev and to have
> > > > consistent naming of the devlink port [1] of a mdev, which is
> > > > formed using phys_port_name of the devlink port, current UUID is
> > > > not usable because UUID is too long.
> > > >
> > > > UUID in string format is 36-characters long and in binary 128-bit.
> > > > Both formats are not able to fit within 15 characters limit of
> > > > netdev
> > name.
> > > >
> > > > It is desired to have mdev device naming consistent using UUID.
> > > > So that widely used user space framework such as ovs [2] can make
> > > > use of mdev representor in similar way as PCIe SR-IOV VF and PF
> > representors.
> > > >
> > > > Hence,
> > > > (a) mdev alias is created which is derived using sha1 from the
> > > > mdev
> > name.
> > > > (b) Vendor driver describes how long an alias should be for the
> > > > child mdev created for a given parent.
> > > > (c) Mdev aliases are unique at system level.
> > > > (d) alias is created optionally whenever parent requested.
> > > > This ensures that non networking mdev parents can function without
> > > > alias creation overhead.
> > > >
> > > > This design is discussed at [3].
> > > >
> > > > An example systemd/udev extension will have,
> > > >
> > > > 1. netdev name created using mdev alias available in sysfs.
> > > >
> > > > mdev UUID=83b8f4f2-509f-382f-3c1e-e6bfe0fa1001
> > > > mdev 12 character alias=cd5b146a80a5
> > > >
> > > > netdev name of this mdev = enmcd5b146a80a5 Here en = Ethernet link
> > > > m = mediated device
> > > >
> > > > 2. devlink port phys_port_name created using mdev alias.
> > > > devlink phys_port_name=pcd5b146a80a5
> > > >
> > > > This patchset enables mdev core to maintain unique alias for a mdev.
> > > >
> > > > Patch-1 Introduces mdev alias using sha1.
> > > > Patch-2 Ensures that mdev alias is unique in a system.
> > > > Patch-3 Exposes mdev alias in a sysfs hirerchy, update
> > > > Documentation
> > > > Patch-4 Introduces mdev_alias() API.
> > > > Patch-5 Extends mtty driver to optionally provide alias generation.
> > > > This also enables to test UUID based sha1 collision and trigger
> > > > error handling for duplicate sha1 results.
> > > >
> > > > [1] http://man7.org/linux/man-pages/man8/devlink-port.8.html
> > > > [2] https://docs.openstack.org/os-vif/latest/user/plugins/ovs.html
> > > > [3] https://patchwork.kernel.org/cover/11084231/
> > > >
> > > > ---
> > > > Changelog:
> > > > v2->v3:
> > > > - Addressed comment from Yunsheng Lin
> > > > - Changed strcmp() ==0 to !strcmp()
> > > > - Addressed comment from Cornelia Hunk
> > > > - Merged sysfs Documentation patch with syfs patch
> > > > - Added more description for alias return value
> > >
> > > Did you get a chance review this updated series?
> > > I addressed Cornelia's and yours comment.
> > > I do not think allocating alias memory twice, once for comparison
> > > and once for storing is good idea or moving alias generation logic
> > > inside the mdev_list_lock(). So I didn't address that suggestion of
> Cornelia.
> >
> > Sorry, I'm at LPC this week. I agree, I don't think the double
> > allocation is necessary, I thought the comment was sufficient to
> > clarify null'ing the variable. It's awkward, but seems correct.
> >
> > I'm not sure what we do with this patch series though, has the real
> > consumer of this even been proposed?

Jiri already acked to use mdev_alias() to generate phys_port_name several days back in the discussion we had in [1].
After concluding in the thread [1], I proceed with mdev_alias().
mlx5_core patches are not yet present on netdev mailing list, but we all agree to use it in mdev_alias() in devlink phys_port_name generation.
So we have collective agreement on how to proceed forward.
I wasn't probably clear enough in previous email reply about it, so adding link here.

[1] https://patchwork.kernel.org/cover/11084231/#22838955

> It feels optimistic to include
> > at this point. We've used the sample driver as a placeholder in the
> > past for mdev_uuid(), but we arrived at that via a conversion rather
> > than explicitly adding the API. Please let me know where the consumer
> > patches stand, perhaps it would make more sense for them to go in
> > together rather than risk adding an unused API. Thanks,
> >
> Given that consumer patch series is relatively large (around 15+ patches), I
> was considering to merge this one as pre-series to it.
> Its ok to combine this with consumer patch series.
> But wanted to have it reviewed beforehand, so that churn is less in actual
> consumer series which is more mlx5_core and devlink/netdev centric.
> So if you can add Review-by, it will be easier to combine with consumer
> series.
>
> And if we merge it with consumer series, it will come through Dave Miller's
> tree instead of your tree.
> Would that work for you?