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Subject: Re: [PATCH net v4 01/12] net: core: limit nested device depth
From:   Johannes Berg <johannes@sipsolutions.net>
To:     Taehee Yoo <ap420073@gmail.com>
Cc:     David Miller <davem@davemloft.net>,
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Date:   Tue, 01 Oct 2019 09:11:10 +0200
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Hi,

Sorry for the delay.

> These functions are used as a callback function of
> netdev_walk_all_{upper/lower}_dev(). So these return types are needed.

Ah yes, I missed that, sorry.

> Without storing level storing, a walking graph routine is needed only
> once. The routine would work as a nesting depth validator.
> So that the detach routine doesn't need to walk the graph.
> Whereas, in this patch, both attach and detach routine need to
> walk graph. So, storing nesting variable way is slower than without
> storing nesting variable way because of the detach routine's updating
> upper and lower level routine.

Right, that's what I thought.

> But I'm sure that storing nesting variables is useful because other
> modules already using nesting level values.
> Please look at vlan_get_encap_level() and usecases.

Indeed, I noticed that later.

> If we don't provide nesting level variables, they should calculate
> every time when they need it and this way is easier way to get a
> nesting level. There are use-cases of lower_level variable
> in the 11th patch.

Yes, makes sense, agree. One could argue that you only ever need the
"lower_level" stored, not the "upper_level", but I guess that doesn't
really make a difference.

Placing these in a better position in the struct might make sense - a
cursory look suggested that they weren't filling any of the many holes
there, did you pay attention to that or was the placement more or less
random?

johannes