netdev - Re: [PATCH v2 net-next 3/5] l2tp: remove l2specific_len dependency in l2tp

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Date:   Mon, 15 Jan 2018 19:54:03 +0100
From:   Guillaume Nault <g.nault@...halink.fr>
To:     Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        James Chapman <jchapman@...alix.com>
Subject: Re: [PATCH v2 net-next 3/5] l2tp: remove l2specific_len dependency
 in l2tp_core

On Mon, Jan 15, 2018 at 07:43:18PM +0100, Lorenzo Bianconi wrote:
> > On Sun, Jan 14, 2018 at 03:50:56PM +0100, Lorenzo Bianconi wrote:
> >> --- a/net/l2tp/l2tp_core.h
> >> +++ b/net/l2tp/l2tp_core.h
> >> @@ -302,6 +302,17 @@ static inline void l2tp_session_dec_refcount(struct l2tp_session *session)
> >>               l2tp_session_free(session);
> >>  }
> >>
> >> +static inline int l2tp_get_l2specific_len(struct l2tp_session *session)
> >> +{
> >> +     switch (session->l2specific_type) {
> >> +     case L2TP_L2SPECTYPE_NONE:
> >> +             return 0;
> >> +     case L2TP_L2SPECTYPE_DEFAULT:
> >> +     default:
> >> +             return 4;
> >> +     }
> >> +}
> >>
> > The data path only compares ->l2specific_type to L2SPECTYPE_DEFAULT and
> > treats any other value as L2SPECTYPE_NONE. Therefore, we should keep
> > this logic here and return 0 for unknown types.
> 
> The data path only compares l2specific_type to L2SPECTYPE_DEFAULT
> since in the other supported case (L2SPECTYPE_NONE) there is no action
> required. Moreover L2SPECTYPE_DEFAULT is default configured value if
> the user does not provide any value for l2specific_type so there are
> no 'unknown' types and I thought L2TP_L2SPECTYPE_DEFAULT was a better
> choice for default value
> 
Yes, but what I meant is that the data patch treats unknow values as
L2SPECTYPE_NONE, while l2tp_get_l2specific_len() now treats them as
L2TP_L2SPECTYPE_DEFAULT. I'd just prefer to avoid that inconsistency;
it makes it easier to reason about the code.

But if you really prefer L2SPECTYPE_DEFAULT, then fine. Unless someone
messes with new l2spec types, we should never reach this case.