RE: [PATCH v2 0/2] Simplify mtty driver and mdev core

[Parav Pandit <parav@mellanox.com>]

> -----Original Message-----
> From: Jiri Pirko <jiri@resnulli.us>
> Sent: Thursday, August 22, 2019 5:50 PM
> To: Parav Pandit <parav@mellanox.com>
> Cc: Alex Williamson <alex.williamson@redhat.com>; Jiri Pirko
> <jiri@mellanox.com>; David S . Miller <davem@davemloft.net>; Kirti
> Wankhede <kwankhede@nvidia.com>; Cornelia Huck <cohuck@redhat.com>;
> kvm@vger.kernel.org; linux-kernel@vger.kernel.org; cjia <cjia@nvidia.com>;
> netdev@vger.kernel.org
> Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core
> 
> Thu, Aug 22, 2019 at 12:04:02PM CEST, parav@mellanox.com wrote:
> >
> >
> >> -----Original Message-----
> >> From: Jiri Pirko <jiri@resnulli.us>
> >> Sent: Thursday, August 22, 2019 3:28 PM
> >> To: Parav Pandit <parav@mellanox.com>
> >> Cc: Alex Williamson <alex.williamson@redhat.com>; Jiri Pirko
> >> <jiri@mellanox.com>; David S . Miller <davem@davemloft.net>; Kirti
> >> Wankhede <kwankhede@nvidia.com>; Cornelia Huck
> <cohuck@redhat.com>;
> >> kvm@vger.kernel.org; linux-kernel@vger.kernel.org; cjia
> >> <cjia@nvidia.com>; netdev@vger.kernel.org
> >> Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core
> >>
> >> Thu, Aug 22, 2019 at 11:42:13AM CEST, parav@mellanox.com wrote:
> >> >
> >> >
> >> >> -----Original Message-----
> >> >> From: Jiri Pirko <jiri@resnulli.us>
> >> >> Sent: Thursday, August 22, 2019 2:59 PM
> >> >> To: Parav Pandit <parav@mellanox.com>
> >> >> Cc: Alex Williamson <alex.williamson@redhat.com>; Jiri Pirko
> >> >> <jiri@mellanox.com>; David S . Miller <davem@davemloft.net>; Kirti
> >> >> Wankhede <kwankhede@nvidia.com>; Cornelia Huck
> >> <cohuck@redhat.com>;
> >> >> kvm@vger.kernel.org; linux-kernel@vger.kernel.org; cjia
> >> >> <cjia@nvidia.com>; netdev@vger.kernel.org
> >> >> Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core
> >> >>
> >> >> Wed, Aug 21, 2019 at 08:23:17AM CEST, parav@mellanox.com wrote:
> >> >> >
> >> >> >
> >> >> >> -----Original Message-----
> >> >> >> From: Alex Williamson <alex.williamson@redhat.com>
> >> >> >> Sent: Wednesday, August 21, 2019 10:56 AM
> >> >> >> To: Parav Pandit <parav@mellanox.com>
> >> >> >> Cc: Jiri Pirko <jiri@mellanox.com>; David S . Miller
> >> >> >> <davem@davemloft.net>; Kirti Wankhede <kwankhede@nvidia.com>;
> >> >> >> Cornelia Huck <cohuck@redhat.com>; kvm@vger.kernel.org;
> >> >> >> linux-kernel@vger.kernel.org; cjia <cjia@nvidia.com>;
> >> >> >> netdev@vger.kernel.org
> >> >> >> Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core
> >> >> >>
> >> >> >> > > > > Just an example of the alias, not proposing how it's set.
> >> >> >> > > > > In fact, proposing that the user does not set it,
> >> >> >> > > > > mdev-core provides one
> >> >> >> > > automatically.
> >> >> >> > > > >
> >> >> >> > > > > > > Since there seems to be some prefix overhead, as I
> >> >> >> > > > > > > ask about above in how many characters we actually
> >> >> >> > > > > > > have to work with in IFNAMESZ, maybe we start with
> >> >> >> > > > > > > 8 characters (matching your "index" namespace) and
> >> >> >> > > > > > > expand as necessary for
> >> >> disambiguation.
> >> >> >> > > > > > > If we can eliminate overhead in IFNAMESZ, let's start with
> 12.
> >> >> >> > > > > > > Thanks,
> >> >> >> > > > > > >
> >> >> >> > > > > > If user is going to choose the alias, why does it
> >> >> >> > > > > > have to be limited to
> >> >> >> sha1?
> >> >> >> > > > > > Or you just told it as an example?
> >> >> >> > > > > >
> >> >> >> > > > > > It can be an alpha-numeric string.
> >> >> >> > > > >
> >> >> >> > > > > No, I'm proposing a different solution where mdev-core
> >> >> >> > > > > creates an alias based on an abbreviated sha1.  The
> >> >> >> > > > > user does not provide the
> >> >> >> alias.
> >> >> >> > > > >
> >> >> >> > > > > > Instead of mdev imposing number of characters on the
> >> >> >> > > > > > alias, it should be best
> >> >> >> > > > > left to the user.
> >> >> >> > > > > > Because in future if netdev improves on the naming
> >> >> >> > > > > > scheme, mdev will be
> >> >> >> > > > > limiting it, which is not right.
> >> >> >> > > > > > So not restricting alias size seems right to me.
> >> >> >> > > > > > User configuring mdev for networking devices in a
> >> >> >> > > > > > given kernel knows what
> >> >> >> > > > > user is doing.
> >> >> >> > > > > > So user can choose alias name size as it finds suitable.
> >> >> >> > > > >
> >> >> >> > > > > That's not what I'm proposing, please read again.
> >> >> >> > > > > Thanks,
> >> >> >> > > >
> >> >> >> > > > I understood your point. But mdev doesn't know how user
> >> >> >> > > > is going to use
> >> >> >> > > udev/systemd to name the netdev.
> >> >> >> > > > So even if mdev chose to pick 12 characters, it could
> >> >> >> > > > result in
> >> collision.
> >> >> >> > > > Hence the proposal to provide the alias by the user, as
> >> >> >> > > > user know the best
> >> >> >> > > policy for its use case in the environment its using.
> >> >> >> > > > So 12 character sha1 method will still work by user.
> >> >> >> > >
> >> >> >> > > Haven't you already provided examples where certain drivers
> >> >> >> > > or subsystems have unique netdev prefixes?  If mdev
> >> >> >> > > provides a unique alias within the subsystem, couldn't we
> >> >> >> > > simply define a netdev prefix for the mdev subsystem and
> >> >> >> > > avoid all other collisions?  I'm not in favor of the user
> >> >> >> > > providing both a uuid and an alias/instance.  Thanks,
> >> >> >> > >
> >> >> >> > For a given prefix, say ens2f0, can two UUID->sha1 first 9
> >> >> >> > characters have
> >> >> >> collision?
> >> >> >>
> >> >> >> I think it would be a mistake to waste so many chars on a
> >> >> >> prefix, but
> >> >> >> 9 characters of sha1 likely wouldn't have a collision before we
> >> >> >> have 10s of thousands of devices.  Thanks,
> >> >> >>
> >> >> >> Alex
> >> >> >
> >> >> >Jiri, Dave,
> >> >> >Are you ok with it for devlink/netdev part?
> >> >> >Mdev core will create an alias from a UUID.
> >> >> >
> >> >> >This will be supplied during devlink port attr set such as,
> >> >> >
> >> >> >devlink_port_attrs_mdev_set(struct devlink_port *port, const char
> >> >> >*mdev_alias);
> >> >> >
> >> >> >This alias is used to generate representor netdev's phys_port_name.
> >> >> >This alias from the mdev device's sysfs will be used by the
> >> >> >udev/systemd to
> >> >> generate predicable netdev's name.
> >> >> >Example: enm<mdev_alias_first_12_chars>
> >> >>
> >> >> What happens in unlikely case of 2 UUIDs collide?
> >> >>
> >> >Since users sees two devices with same phys_port_name, user should
> >> >destroy
> >> recently created mdev and recreate mdev with different UUID?
> >>
> >> Driver should make sure phys port name wont collide,
> >So when mdev creation is initiated, mdev core calculates the alias and if there
> is any other mdev with same alias exist, it returns -EEXIST error before
> progressing further.
> >This way user will get to know upfront in event of collision before the mdev
> device gets created.
> >How about that?
> 
> Sounds fine to me. Now the question is how many chars do we want to have.
> 
12 characters from Alex's suggestion similar to git?

> >
> >
> >> in this case that it does
> >> not provide 2 same attrs for 2 different ports.
> >> Hmm, so the order of creation matters. That is not good.
> >>
> >> >>
> >> >> >I took Ethernet mdev as an example.
> >> >> >New prefix 'm' stands for mediated device.
> >> >> >Remaining 12 characters are first 12 chars of the mdev alias.
> >> >>
> >> >> Does this resolve the identification of devlink port representor?
> >> >Not sure if I understood your question correctly, attemping to answer
> below.
> >> >phys_port_name of devlink port is defined by the first 12 characters
> >> >of mdev
> >> alias.
> >> >> I assume you want to use the same 12(or so) chars, don't you?
> >> >Mdev's netdev will also use the same mdev alias from the sysfs to
> >> >rename
> >> netdev name from ethX to enm<mdev_alias>, where en=Etherenet,
> m=mdev.
> >> >
> >> >So yes, same 12 characters are use for mdev's netdev and mdev
> >> >devlink port's
> >> phys_port_name.
> >> >
> >> >Is that what are you asking?
> >>
> >> Yes. Then you have 3 chars to handle the rest of the name (pci, pf)...