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

[Parav Pandit]

Hi Alex,


> -----Original Message-----
> From: Jiri Pirko <jiri@xxxxxxxxxxx>
> Sent: Friday, August 23, 2019 1:42 PM
> To: Parav Pandit <parav@xxxxxxxxxxxx>
> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>; Jiri Pirko
> <jiri@xxxxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>; Kirti
> Wankhede <kwankhede@xxxxxxxxxx>; Cornelia Huck <cohuck@xxxxxxxxxx>;
> kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; cjia <cjia@xxxxxxxxxx>;
> netdev@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core
> 
> Thu, Aug 22, 2019 at 03:33:30PM CEST, parav@xxxxxxxxxxxx wrote:
> >
> >
> >> -----Original Message-----
> >> From: Jiri Pirko <jiri@xxxxxxxxxxx>
> >> Sent: Thursday, August 22, 2019 5:50 PM
> >> To: Parav Pandit <parav@xxxxxxxxxxxx>
> >> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>; Jiri Pirko
> >> <jiri@xxxxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>; Kirti
> >> Wankhede <kwankhede@xxxxxxxxxx>; Cornelia Huck
> <cohuck@xxxxxxxxxx>;
> >> kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; cjia
> >> <cjia@xxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx
> >> Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core
> >>
> >> Thu, Aug 22, 2019 at 12:04:02PM CEST, parav@xxxxxxxxxxxx wrote:
> >> >
> >> >
> >> >> -----Original Message-----
> >> >> From: Jiri Pirko <jiri@xxxxxxxxxxx>
> >> >> Sent: Thursday, August 22, 2019 3:28 PM
> >> >> To: Parav Pandit <parav@xxxxxxxxxxxx>
> >> >> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>; Jiri Pirko
> >> >> <jiri@xxxxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>; Kirti
> >> >> Wankhede <kwankhede@xxxxxxxxxx>; Cornelia Huck
> >> <cohuck@xxxxxxxxxx>;
> >> >> kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; cjia
> >> >> <cjia@xxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx
> >> >> Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core
> >> >>
> >> >> Thu, Aug 22, 2019 at 11:42:13AM CEST, parav@xxxxxxxxxxxx wrote:
> >> >> >
> >> >> >
> >> >> >> -----Original Message-----
> >> >> >> From: Jiri Pirko <jiri@xxxxxxxxxxx>
> >> >> >> Sent: Thursday, August 22, 2019 2:59 PM
> >> >> >> To: Parav Pandit <parav@xxxxxxxxxxxx>
> >> >> >> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>; Jiri Pirko
> >> >> >> <jiri@xxxxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>;
> >> >> >> Kirti Wankhede <kwankhede@xxxxxxxxxx>; Cornelia Huck
> >> >> <cohuck@xxxxxxxxxx>;
> >> >> >> kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; cjia
> >> >> >> <cjia@xxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx
> >> >> >> Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core
> >> >> >>
> >> >> >> Wed, Aug 21, 2019 at 08:23:17AM CEST, parav@xxxxxxxxxxxx wrote:
> >> >> >> >
> >> >> >> >
> >> >> >> >> -----Original Message-----
> >> >> >> >> From: Alex Williamson <alex.williamson@xxxxxxxxxx>
> >> >> >> >> Sent: Wednesday, August 21, 2019 10:56 AM
> >> >> >> >> To: Parav Pandit <parav@xxxxxxxxxxxx>
> >> >> >> >> Cc: Jiri Pirko <jiri@xxxxxxxxxxxx>; David S . Miller
> >> >> >> >> <davem@xxxxxxxxxxxxx>; Kirti Wankhede
> >> >> >> >> <kwankhede@xxxxxxxxxx>; Cornelia Huck <cohuck@xxxxxxxxxx>;
> >> >> >> >> kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; cjia
> >> >> >> >> <cjia@xxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx
> >> >> >> >> 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?
> 
> Ok.
> 

Can you please confirm this scheme looks good now? I like to get patches started.

> >
> >> >
> >> >
> >> >> 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)...