hello, I'm having hard time trying to remember sin6_flowinfo semantics.
RFC2553/2292 are not very clear to me. for example, could someone
answer these questions?
(1) on recvfrom, how sin6_flowinfo should be filled?
(2) on sendto, how will the kernel interpret sin6_flowinfo from the
userland?
(3) any other interface to manipulate traffic class/flow label?
from my personal email archive, there are mixed opinions, and the
discussion did not reflected into 2553/2292.
- Eric's summary: (IPng 6324)
(1) sin6_flowinfo will be filled by ip6->ip6_flow.
(2) sin6_flowinfo will be copied into ip6->ip6_flow.
if you do not want any special behavior, userland programs should
fill it by 0.
(3) nope.
>No, it just means that the naive flow label unaware UDP application
>needs to clear sin6_flowinfo in the address it got from recvfrom
>before it uses that address in a sendto call. That is what we will document
>here at Sun.
- Alexey's summary: (IPng 6334)
(1) sin6_flowinfo will be filled by zero.
(2) sin6_flowinfo must carry traffic class bits only.
(3) setsockopt or ancillary data (but how?).
>The conclusion: sin6_flowinfo mbz in recvfrom(), and may contain
>only class bits in sendto(). It is much more convenient to make with
>setsockopt() or ancillary data.
It seems to me that Eric is more in sync with the current documents,
since there's no standard setsockopt nor ancillary data to manipulate
traffic class/flow label fields.
i'd love to see it clarificed in near future 2553bis/2292bis.
itojun
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