netdev - Re: [RFC PATCH 0/2] add ppp_generic ioctl to bridge channels

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Date:   Tue, 17 Nov 2020 12:12:23 +0000
From:   Tom Parkin <tparkin@...alix.com>
To:     Guillaume Nault <gnault@...hat.com>
Cc:     netdev@...r.kernel.org, jchapman@...alix.com
Subject: Re: [RFC PATCH 0/2] add ppp_generic ioctl to bridge channels

On  Sun, Nov 15, 2020 at 12:59:59 +0100, Guillaume Nault wrote:
> On Tue, Nov 10, 2020 at 11:54:07AM +0000, Tom Parkin wrote:
> > On  Mon, Nov 09, 2020 at 23:51:53 +0100, Guillaume Nault wrote:
> > > BTW, shouldn't we have an "UNBRIDGE" command to remove the bridge
> > > between two channels?
> > 
> > I'm not sure of the usecase for it to be honest.  Do you have
> > something specific in mind?
> 
> I don't know if there'd be a real production use case. I proposed it
> because, in my experience, the diffucult part of any new feature is
> the "undo" operation. That's where many race conditions are found.
> 
> Having a way to directly revert a BRIDGE operation might help testing
> the undo path (otherwise it's just triggered as a side effect of
> closing a file descriptor). I personally find that having symmetrical
> "do" and "undo" operations helps me thinking precisely about how to
> manage concurency. But that's probably a matter of preference. And that
> can even be done without exposing the "undo" operation to user space
> (it's just more difficult to test).
> 
> Anyway, that was just a suggestion. I have no strong opinion.

Thanks for clarifying the point -- I agree with you about the "undo"
operation helping to expose race conditions.

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