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From:   Parav Pandit <parav@mellanox.com>
To:     Alex Williamson <alex.williamson@redhat.com>
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Subject: RE: [PATCH 0/4] Introduce variable length mdev alias
Thread-Topic: [PATCH 0/4] Introduce variable length mdev alias
Thread-Index: AQHVXE6oE0YRBz0PMky+S05YIDBwe6cO90UwgABPfgCAAASicA==
Date:   Tue, 27 Aug 2019 18:11:32 +0000
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> -----Original Message-----
> From: Alex Williamson <alex.williamson@redhat.com>
> Sent: Tuesday, August 27, 2019 11:19 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 0/4] Introduce variable length mdev alias
>=20
> On Tue, 27 Aug 2019 13:11:17 +0000
> Parav Pandit <parav@mellanox.com> wrote:
>=20
> > Hi Alex, Cornelia,
> >
> > > -----Original Message-----
> > > From: kvm-owner@vger.kernel.org <kvm-owner@vger.kernel.org> On
> > > Behalf Of Parav Pandit
> > > Sent: Tuesday, August 27, 2019 2:11 AM
> > > 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 0/4] 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=3D83b8f4f2-509f-382f-3c1e-e6bfe0fa1001
> > > mdev 12 character alias=3Dcd5b146a80a5
> > >
> > > netdev name of this mdev =3D enmcd5b146a80a5 Here en =3D Ethernet lin=
k m
> > > =3D mediated device
> > >
> > > 2. devlink port phys_port_name created using mdev alias.
> > > devlink phys_port_name=3Dpcd5b146a80a5
> > >
> > > 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.
> > > Patch-4 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.
> > >
> > > In future when networking driver wants to use mdev alias,
> > > mdev_alias() API will be added to derive devlink port name.
> > >
> > Now that majority of above patches looks in shape and I addressed all
> > comments, In next v1 post, I was considering to include mdev_alias()
> > and have example use in mtty driver.
> >
> > This way, subsequent series of mlx5_core who intents to use
> > mdev_alias() API makes it easy to review and merge through Dave M,
> > netdev tree. Is that ok with you?
>=20
> What would be the timing for the mlx5_core use case?  Can we coordinate
> within the same development cycle?  I wouldn't want someone to come
> clean up the sample driver and remove the API ;)  Thanks,
>=20
We targeted it for 5.4. mdev_alias was the only known user interface issue,=
 which is resolved.
Some more internal reviews are in progress.
It might be tight for 5.4, if not 5.4, it should happen in 5.5.

I agree, that is why I was holding up to be part of this series.
Since its very small API, even if there is any merge conflict, it is easy t=
o resolve.
If this change can be merged through netdev tree, its better to include it =
as part of mlx5_core's mdev series.
So both options are fine, a direction from you is better to have.