On Wed, Dec 01, 2021 at 12:30:10PM +0100, Florian Westphal wrote:
> Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote:
> > On Tue, Nov 23, 2021 at 02:37:42PM +0100, Florian Westphal wrote:
> > > Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> wrote:
> > > > On Fri, Nov 19, 2021 at 04:28:39PM +0100, Florian Westphal wrote:
> > > > > Because the subtype is only 4 bits in size the exthdr
> > > > > delinearization needs a fixup to remove the binop added by the
> > > > > evaluation step.
> > > >
> > > > By the bitwise operation to take the 4 bits you can infer this refers to
> > > > mptcp, but it might be good to store in the rule userdata area that this
> > > > expression refers to mptcp as a suggestion to userspace when
> > > > delinearizing the rule.
> > >
> > > Why? Userspace has all info: its a tcp option, we have the tcp option
> > > number (mptcp) and a 4 bit field which matches the template field.
> > >
> > > There is no guesswork here.
> >
> > OK, thanks for explaining.
>
> I can add a commet before pushing this out.
Please add a comment and push out this.
> 'tcp option == mptcp' always allows to take those 4 bit to identify
> the next subheader.
>
> The only caveat is that some suboptions have different sizes depending
> on the option length field, this will get more complicated once matching
> on those is added (we will need to take moer dependencies into account).
This might require to extend the dependency infrastructure.
> > > > > One remaining usablility problem is the lack of mnemonics for the
> > > > > subtype, i.e. something like:
> > > > >
> > > > > static const struct symbol_table mptcp_subtype_tbl = {
> > > > > .base = BASE_DECIMAL,
> > > > > .symbols = {
> > > > > SYMBOL("mp-capable", 0),
> > > > > SYMBOL("mp-join", 1),
> > > > > SYMBOL("dss", 2),
> > > > > SYMBOL("add-addr", 3),
> > > > > SYMBOL("remove-addr", 4),
> > > > > SYMBOL("mp-prio", 5),
> > > > > SYMBOL("mp-fail", 6),
> > > > > SYMBOL("mp-fastclose", 7),
> > > > > SYMBOL("mp-tcprst", 8),
> > > > > SYMBOL_LIST_END
> > > > > },
> > > > >
> > > > > ... but this would need addition of yet another data type.
> > > > >
> > > > > Use of implicit/context-dependent symbol table would
> > > > > be preferrable, I will look into this next.
> > > >
> > > > Could you develop your idea?
> > >
> > > No idea, I have not thought about it at all. I do not want
> > > to add a new data type for this.
> > >
> > > One way is to just extend the scanner with even more keywords.
> > > I tought I could annotate the eval context with 'saw mptcp'
> > > and then use that when trying to resolve the symbol expressions.
> > >
> > > No idea if that works and no idea how much hassle that is.
> >
> > You can probably use a string in the parser for these types, then
> > invoke the symbol_table lookup from the parser to fetch the value?
>
> Current solution I'm working on adds a phony integer type, similar
> to the 'hex output' one.
>
> Delinearization needs to do some extra steps to override the integer
> again though.
>
> I will share some draft patches soon.
Sounds good, please consider the typeof path for set/map too.
