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ipv6.7: Document IPV6_RECVPKTINFO 

Notes from Bert Hubert:
    Recently PowerDNS needed to support the getting of the
    original destination address of packets received on ::.
    Following the advice in ipv6(7) generated an error on
    setsockopt().

    Some googling confirmed that setsockopt() with
    IPV6_PKTINFO indeed does not work, but we found that
    IPV6_RECVPKTINFO did.

   Our experiences are detailed in
   http://bert-hubert.blogspot.nl/2012/10/on-binding-datagram-udp-sockets-to-any.html

    Please find attached a quite naive patch to ipv6.7 that at
    least fixes 'my' problem, but does not document if
    IPV6_PKTINFO ever worked as a flag. It does document that
    IPV6_RECVPKTINFO is available since 2.6.13.

    Please let me know if this patch is acceptable, or if you
    want me to dig deeper into the IPV6_PKTINFO situation.

Notes from mtk:
    Drop mention of IPV6_PKTINFO; that's IPV6_2292PKTINFO nowadays
    (and needs to be documented). And, confusingly, there's nowadays
    an IPV6_PKTINFO that is a quite different thig.

    With kernel commit 333fad5364d6b457c8d837f7d05802d2aaf8a961
    (Sep 2005) PV6_PKTINFO disappeared from the
    getsockopt/setsockopt API, and IPV6_2292PKTINFO took its place.
    Meanwhile, IPV6_RECVPKTINFO was added.

    Then kernel commit b24a2516d10751d7ed5afb58420df25370c9dffb
    (Dec 2008) added IPV6_PKTINFO back to the
    getsockopt/getsockopt API, but with what looks to be a
    rather different meaning (it takes a 'struct in6_pktinfo'
    as the third arg).

    This seems consistent (if confusing) with the RFCs:
    http://www.ietf.org/rfc/rfc2292.txt
    http://www.ietf.org/rfc/rfc3542.txt (obsoletes 2292)

    Both of those RFCs define an IPV6_PKTINO sockopt, but the
    former takes an int arg, and the latter takes a
    'struct in6_pktinfo'.

    So, my summary of your patch is that it's correct. (But I think
    that IPV6_RECVPKTINFO is present since 2.6.14, not 2.6.13.)

Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
This commit is contained in:
Bert Hubert 2012-10-21 12:51:33 +02:00 committed by Michael Kerrisk
parent 251da60bbb
commit d796c68d5a
1 changed files with 4 additions and 3 deletions
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7
man7/ipv6.7
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@ -4,7 +4,7 @@
.\" and in case of nontrivial modification author and date .\" and in case of nontrivial modification author and date
.\" of the modification is added to the header. .\" of the modification is added to the header.
.\" $Id: ipv6.7,v 1.3 2000/12/20 18:10:31 ak Exp $ .\" $Id: ipv6.7,v 1.3 2000/12/20 18:10:31 ak Exp $
.TH IPV6 7 2012-05-10 "Linux" "Linux Programmer's Manual" .TH IPV6 7 2012-10-12 "Linux" "Linux Programmer's Manual"
.SH NAME .SH NAME
ipv6 \- Linux IPv6 protocol implementation ipv6 \- Linux IPv6 protocol implementation
.SH SYNOPSIS .SH SYNOPSIS
@ -141,7 +141,7 @@ structure.
.\" FIXME IPV6_CHECKSUM is not documented, and probably should be .\" FIXME IPV6_CHECKSUM is not documented, and probably should be
.\" FIXME IPV6_JOIN_ANYCAST is not documented, and probably should be .\" FIXME IPV6_JOIN_ANYCAST is not documented, and probably should be
.\" FIXME IPV6_LEAVE_ANYCAST is not documented, and probably should be .\" FIXME IPV6_LEAVE_ANYCAST is not documented, and probably should be
.\" FIXME IPV6_RECVPKTINFO is not documented, and probably should be .\" FIXME IPV6_PKTINFO is not documented, and probably should be
.\" FIXME IPV6_2292PKTINFO is not documented, and probably should be .\" FIXME IPV6_2292PKTINFO is not documented, and probably should be
.\" FIXME there are probably many other IPV6_* socket options that .\" FIXME there are probably many other IPV6_* socket options that
.\" should be documented .\" should be documented
@ -183,10 +183,11 @@ in an integer.
Control whether the socket sees multicast packets that it has send itself. Control whether the socket sees multicast packets that it has send itself.
Argument is a pointer to boolean. Argument is a pointer to boolean.
.TP .TP
.B IPV6_PKTINFO .BR IPV6_RECVPKTINFO " (since Linux 2.6.14)"
Set delivery of the Set delivery of the
.B IPV6_PKTINFO .B IPV6_PKTINFO
control message on incoming datagrams. control message on incoming datagrams.
Such control messages contain a struct in6_pktinfo, as per RFC 3542.
Only allowed for Only allowed for
.B SOCK_DGRAM .B SOCK_DGRAM
or or