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SubjectRe: sendmsg and IP_PKTINFO
On Tuesday February 18, wrote:
> Hello,
> Neil Brown wrote:
> > Note that the in_pktinfo is described as "some information about the
> > incoming packet". In particular ipi_ifindex is "the unique index of
> > the interface the packets was received on".
> >
> > i.e. it is more about the incoming than the outgoing packet.
> Yes, because when set as socket option you can receive
> pktinfo with recvmsg. But IP_PKTINFO can be used also with sendmsg.
> Just forget about interfaces, i.e. use something like this in cmsg:
> .ipi = {
> .ipi_ifindex = 0,
> .ipi_spec_dst = local_ip,
> },

Certainly IP_PKTINFO can be used with sendmsg. The doesn't change the
fact that the documentation clearly says that the information is
information about an incoming packet.

Also, th only documentation I can find does not specify that a value
of 0 means "no specific interface is selected". So while I can see
from the code that what you suggest would work in practice, it would
be nice if this were clearly documented somewhere.


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