On Thu, 17 Aug 2023 10:10:35 +0100 Donald Hunter wrote:
> > Looks good, but do we also need some extra plumbing to decode extack
> > for classic netlink correctly? Basically shouldn't _decode_extack()
> > also move to proto? Or we can parameterize it? All we really need there
> > is to teach it how much of fixed headers parser needs to skip to get to
> > attributes, really (which, BTW is already kinda buggy for genl families
> > with fixed headers).
>
> I have been working on the assumption that extack responses don't
> include any fixed headers. I have seen extack messages decoded correctly
> for classic netlink, here with RTM_NEWROUTE:
>
> lib.ynl.NlError: Netlink error: Invalid argument
> nl_len = 80 (64) nl_flags = 0x300 nl_type = 2
> error: -22 extack: {'msg': 'Invalid prefix for given prefix length'}
>
> Is there something I am missing?
I'm thinking of extack messages carrying offsets in addition to the
textual error message. NLMSGERR_ATTR_OFFS or NLMSGERR_ATTR_MISS_NEST.
In that case ynl will try to re-parse its own message via
_decode_extack_path() to resolve from the offset to what attribute
was there. See the commit message on a552bfa16:
lib.ynl.NlError: Netlink error: Numerical result out of range
nl_len = 108 (92) nl_flags = 0x300 nl_type = 2
error: -34 extack: {'msg': 'integer out of range',...
'bad-attr': '.ifindex'}
I mean the "bad-attr" thing.
I think it works out of sheer luck here, we happen to skip over
the fixed header because it looks like a 0-length attribute?
