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

Parav Pandit
2019-09-13T23:20:04Z

Hi Alex,

> -----Original Message-----
> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Friday, September 13, 2019 4:33 PM
> 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 Wed, 11 Sep 2019 16:38:49 +0000
> Parav Pandit <parav@mellanox.com> wrote:
>
> > > -----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
>
> Jiri may have agreed to the concept, but without patches on the list proving an
> end to end solution, I think it's too early for us to commit to this by
> preemptively adding it to our API. "Acked" and "collective agreement" seem
> like they overstate something that seems not to have seen the light of day yet.
> Instead I'll say, it looks reasonable, come back when the real consumer has
> actually been proposed upstream and has more buy-in from the community
> and we'll see if it still looks like the right approach from an mdev perspective
> then. Thanks,
>
Ok. I will combine these patches with the actual consumer patches of mdev_alias().
Thanks.

> Alex