Re: [PATCH 2/2][MCAST] Fix for add_grec(...)

[Yan Zheng]

David Stevens wrote:
> Yan,
>         I think your patch has some problems.
>
> Yan Zheng <yanzheng@xxxxxxxx> wrote on 11/09/2005 03:58:20 AM:
>
>
> > +#if 0
> >    if (!*psf_list) {
> >       if (type == MLD2_ALLOW_NEW_SOURCES ||
> >           type == MLD2_BLOCK_OLD_SOURCES)
> > @@ -1474,12 +1477,15 @@ static struct sk_buff *add_grec(struct s
> >       }
> >       return skb;
> >    }
> > +#endif
>
>
>
>         This code is the only place in the current code where you
> can generate a group header with an empty source list (what it is
> checking for). Your patch has added an add_grhead() for change
> and EXCLUDE records, but it isn't checking mca_crcount or isquery.
> I need to check, but I'm concerned this will create a group header
> in a report for cases where it should not.
ischange implicits mca_crcount has already been ckecked in mld_send_cr(...)
Actually, check mca_crcount directly will get mode change report sent one times less 
than you intend, because mca_crcount has decreased by one before call add_grec(...).


Now We only have MLD2_MODE_IS_INCLUDE left. but "mode is include and source list is empty"
is an impossible event.
> >    pmr = skb ? (struct mld2_report *)skb->h.raw : NULL;
> >
> >    /* EX and TO_EX get a fresh packet, if needed */
> > -   if (truncate) {
> > -      if (pmr && pmr->ngrec &&
> > -          AVAILABLE(skb) < grec_size(pmc, type, gdeleted, sdeleted)) {
> > +   if (truncate || ischange) {
> > +      int min_len;
> > +      min_len   = truncate ? grec_size(pmc, type, gdeleted, sdeleted) : 
>
>
> > +           (sizeof(struct mld2_grec) + sizeof(struct in6_addr));
> > +      if (pmr && pmr->ngrec && AVAILABLE(skb) < min_len) {
> >          if (skb)
> >             mld_sendpack(skb);
> >          skb = mld_newpack(dev, dev->mtu);
>
>
>         This "truncate" code is to handle exclude records that may be
> truncated. It gets a new packet when adding this record and the whole
> thing won't fit in a single packet. This is not appropriate for anything
> but IS_EX and TO_EX, but "ischange" in your patch will be true for
> TO_IN. So, I think this will waste space in a report that could hold
> some of these TO_IN sources.

When type is MLD2_MODE_IS_INCLUDE, min_len is equal to "sizeof(struct mld2_grec) + 
sizeof(struct in6_addr)". it satisfies the comment above. (make sure we have room 
for group header and at least one source.)

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