netdev - Re: [RFC net-next 0/6] xdp: make stack perform remove and tests

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Date:   Sat, 25 Nov 2017 17:43:04 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     netdev@...r.kernel.org, oss-drivers@...ronome.com,
        daniel@...earbox.net, jiri@...nulli.us
Subject: Re: [RFC net-next 0/6] xdp: make stack perform remove and tests

On Sat, 25 Nov 2017 17:02:09 -0800, Alexei Starovoitov wrote:
> On Thu, Nov 23, 2017 at 06:36:07PM -0800, Jakub Kicinski wrote:
> > Hi!
> > 
> > The purpose of this series is to add a software model of BPF offloads
> > to make it easier for everyone to test them and make some of the more
> > arcane rules and assumptions more clear.
> > 
> > The series starts with 3 patches aiming to make XDP handling in the
> > drivers less error prone.  Currently driver authors have to remember
> > to free XDP programs if XDP is active during unregister.  With this
> > series the core will disable XDP on its own.  It will take place
> > after close, drivers are not expected to perform reconfiguration
> > when disabling XDP on a downed device.
> > 
> > Next two patches add the software netdev driver.  Last but not least
> > there is a python test which exercises all the corner cases which
> > came to my mind.
> > 
> > Test needs to be run as root.  It will print basic information to
> > stdout, but can also create a more detailed log of all commands
> > when --log option is passed.  Log is in Emacs Org-mode format.
> > 
> >   ./tools/testing/selftests/bpf/test_offload.py --log /tmp/log
> > 
> > Something I'm still battling with, and would appreciate help of
> > wiser people is that occasionally during the test something makes
> > the refcount of init_net drop to 0 :S  I tried to create a simple
> > reproducer, but seems like just running the script in the loop is
> > the easiest way to go...  Could it have something to do with the
> > recent TC work?  The driver is pretty simple and never touches
> > ref counts.  The only slightly unusual thing is that the BPF code
> > sleeps for a bit on remove in the netdev notifier.  
> 
> I like the direction.
> Patch 3 in particular with auto prog_put is a great idea!
> Patch 4 - if you want to do dual gpl+bsd. It's ok and really your call as an author.
> Patch 5 - I'm only not excited about debugfs. Can you do the same with tracepoints?

I would prefer to stick to DebugFS, if you don't mind.  Some of the
knobs are writeable.  I look at DebugFS as a back door.  We throw
standard API commands at the device and want to inspect its internal
state.  And cross check the standard reporting APIs.  As such DebugFS
is completely inappropriate but for API-test-drivers.

On that topic - is there a way to trigger and wait for an rcu barrier
from user space?  Quentin pointed out that selftest is shaky unless run
with RCU debug enabled.  To wait for deletion of programs I need a
barrier :S

> Patch 6 - python 3 is a requirement? or can work with 2.7 ? I don't mind if it's 3+ only.
> Just trying to understand the dependencies.

Am a python noob so I defaulted to version 3 and proceeded to look
things I needed up in the python 3 docs.  Which perhaps resulted in
using more python3 only features than necessary...  

Upon a quick inspection, the only python3 feature I seem to be using 
is the Popen.args member.

> and thanks for adding it to selftests.

Thanks for the comments!