Re: [tcpdump] After setjmp/longjmp update

[Denis Ovsienko via tcpdump-workers <tcpdump-workers () lists tcpdump org>]

> --- Begin Message ---
>
>
> From: Denis Ovsienko <denis () ovsienko info>
>
> Date: Tue, 8 Sep 2020 05:40:35 +0100
>
> On Mon, 7 Sep 2020 17:26:28 +0200
> Francois-Xavier Le Bail <devel.fx.lebail () orange fr> wrote:
>
> > On 07/09/2020 16:43, Denis Ovsienko via tcpdump-workers wrote:
> > > On Sat, 5 Sep 2020 18:20:42 +0200
> > > Thank you for posting a detailed explanation and making the first
> > > round of changes. I am looking into the logic of this work. As soon
> > > as it feels I can tell the right instances of ND_TCHECK() to remove
> > > from the wrong ones, I am going to convert some more code manually
> > > if that's OK.  
> >
> > That's OK, just try to avoid those like:
> >
> > ND_TCHECK_LEN(e, sizeof(nd_ipv4)) calls followed by a
> > GET_IPADDR_STRING(e) call, same e.
> >
> > ND_TCHECK_4(e) calls followed by a GET_IPADDR_STRING(e) call, same e.
> >
> > ND_TCHECK_LEN(e, sizeof(nd_ipv6)) calls followed by a
> > GET_IP6ADDR_STRING(e) call, same e.
> >
> > ND_TCHECK_16(e) calls followed by a GET_IP6ADDR_STRING(e) call, same
> > e.
> >
> > (I am working to remove them)
>
> My commit is in the master branch, I tried not to touch the patterns
> above and to make only the changes that are obviously safe.
>
> Regarding the loss of ability to skip the link layer header on a
> pseudo-return via longjmp(), is there a formal definition (or at least
> a workable convention) of a link layer header? For example,
> ether_if_print() can return one value for ordinary Ethernet and another
> for ordinary Ethernet inside Arista Ethernet.
>
> I do not understand yet if it would be right in theory to increment
> ndo_ll_hdr_len each time a decoder has retrieved another complete link
> layer header and is about to dig deeper, and how hard in practice it
> would be to do that in all DLT printers. Maybe it could be a simpler
> problem to solve if the current DLT printer functions were setting
> ndo_ll_hdr_len to a sensible DLT-specific value just once before a full
> decode, not after.
>
> Does it make sense?
>
> -- 
>     Denis Ovsienko
>
> --- End Message ---
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