On 2012-06-03 15:24, Phil Pennock wrote:
On 2012-06-03 at 09:58 -0400, Phil Pennock wrote:
Variable: still not quite sure about exposing this, or if perhaps it
should be an expansion item rather than a variable, so that each time
it's expanded the value is fetched. Er, I'm also blanking on how to
*implement* this with a read()-based API, without switching our entire
SMTP read system to a readmsg()-based system, which I'm *very* reluctant
to do for such a minor feature.
Stevens, Unix Network Programming, volume 1 3rd edition (Stevens,
Fenner, Rudoff), page 215, under "IP_TOS Socket Option":
This option lets us set the type-of-service (TOS) field (which
contains the DSCP and ECN fields, Figure A.1) in the IP header for a
TCP, UDP or SCTP socket. If we call getsockopt for this option, the
current value that would be placed into the DSCP and ECN fields in the
IP header (which defaults to 0) is returned. There is no way to fetch
the value from a received IP datagram.
That last sentence clinches it, there will not be a
$received_initial_dscp or $received_dscp added to Exim.
Seems like a lack in the available interface rather than anything
fundamental, but given how long those bit-positions have been lying around
unused in the ipv4 header I really doubt that many people care.
Should the position be (or become) different in some OS we want
to support we can revisit; as you note an expansion item would
be preferable to a variable (even if a first implementation
could only support the connect-time value, IMHO).
--
Jeremy
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