netdev - Re: [patch net-next rfc 00/15] netdevsim: impement proper device model

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Date:   Mon, 15 Apr 2019 12:27:09 -0700
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, mlxsw@...lanox.com
Subject: Re: [patch net-next rfc 00/15] netdevsim: impement proper device
 model

On Sat, 13 Apr 2019 18:20:57 +0200, Jiri Pirko wrote:
> From: Jiri Pirko <jiri@...lanox.com>
> 
> Currently the model of netdevsim is a bit odd in multiple ways.
> 1) devlink instance is not in any way related with actual netdevsim
>    netdevices. Instead, it is created per-namespace.
> 2) multi-port netdevsim device is done using "link" attribute.
> 3) netdevsim bus is there only to have something to bind the netdev to,
>    it really does not act as a bus.

Nope, it's there to expose SR-IOV ops :)

> 4) netdevsim instances are created by "ip link add" which is great for
>    soft devices with no hw backend. The rtnl core allocates netdev and
>    calls into driver holding rtnl mutex. For hw-backed devices, this
>    flow is wrong as it breaks order in which things are done.
> 
> This patchset adjust netdevsim to fix all above.
> 
> In order to support proper devlink and devlink port instances and to be
> able to emulate real devices, there is need to implement bus probe and
> instantiate everything from there. User can specify device id and port
> count to be instantianted. For example:
> 
> echo "10 4" > /sys/bus/netdevsim/new_device

I really don't like the design where ID has to be allocated by user
space.  It's a step back.

I also dislike declaring ports from the start.  In real drivers ports
are never "atomically" registered, they are crated and destroyed one 
by one, and a lot of races/UAFs/bugs lie in those small periods of
time where one netdev got unregistered, but other are still around...

> Then devlink shows this:
> 
> $ devlink dev
> netdevsim/netdevsim10
> 
> $ devlink port
> netdevsim/netdevsim10/0: type eth netdev netdevsim10p1 flavour physical
> netdevsim/netdevsim10/1: type eth netdev netdevsim10p2 flavour physical
> netdevsim/netdevsim10/2: type eth netdev netdevsim10p3 flavour physical
> netdevsim/netdevsim10/3: type eth netdev netdevsim10p4 flavour physical
> 
> Debugfs topology is also adjusted a bit. The rest stays the same as
> before.
> 
> TODO:
> - teach udev to rename netdevsim netdevices similarly to pci netdevices

So we can test udev as well?

> - fix tools/testing/selftests/bpf/test_offload.py to work with new iface

That'd step 0 :)

BTW are you testing all this with the various sysfs/kobject debug
checks?  I don't remember all the deets now, but there were certainly
ordering considerations coming from there.