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    SubjectRE: [PATCH v2 0/2] Simplify mtty driver and mdev core
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    > -----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)...

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