Re: [tsvwg] A review of draft-ietf-tsvwg-udp-options-12

["C. M. Heard" <[e-mail]>]

On Sun, Jun 13, 2021 at 7:12 PM Joseph Touch <[e-mail]> wrote:

> Finally, regarding FRAG:
> - we need to decide whether we want to support zero-copy (probably a
> better way of putting it than RDMA)
>         if so, then we should also consider whether to allow options after
> non-terminal fragments
>         that would operate on the fragment only (this would help reduce
> the amount of data that needs to be moved
>         to allow zero copy)
>
> - either way
>         - non-terminal fragments MUST use FRAG last
>         - terminal fragments include post-FRAG options that operate on the
> entire reassembled fragment
>
> If we DO NOT support zero-copy, the format would be:
>
>         Nonterminal format, where OPTLEN = 8
>                 KIND/8, OPTLEN/8, FRAGOFFSET/16
>                 FRAGID/32
>
>         Terminal format, where OPTLEN = 10
>                 KIND/8, OPTLEN/8, FRAGOFFSET/16
>                 FRAGID/32
>                 THISFRAGLEN/16
>
>         FRAGOFFSET = where to place the fragment in the reassembled user
> data
>         THISFRAGLEN = length of the terminal fragment, i.e., indicating
> where the post-frag options resume
>
>         (note - this is what we have in the current draft, version -12,
> except it swaps FRAGOFFSET and THISFRAGLEN
>         and omits it from non-terminal fragments)
>
> If we DO support zero-copy and thus want to allow non-terminal fragments
> to have post-fragoption options that operate on each fragment, then we
> would add THISFRAGLEN to the nonterminal format and issue different KIND
> numbers to nonterminal/terminal fragment.
>


I for one would appreciate further discussion of these last points. I admit
that I have failed to grasp Joe's message on the RDMA thread, and I would
appreciate some time to think about it.

Thanks

Mike