Socket sendmsg() porting question
johannes at brilliantservice.co.jp
Wed Aug 3 17:18:39 UTC 2016
Thanks for the reply.
Can I still use the same receiving function for sendmsg/send and tell what
kind of message is coming?
How would I tell if there is an fd attached or not?
Even if I set cmsg_level and cmsg_type it won't let me send it. The problem
is having a zero length attachment on freebsd....
I can't send -1 as fd because that errors to invalid file descriptor.
On Wed, Aug 3, 2016 at 10:12 AM, Alan Somers <asomers at freebsd.org> wrote:
> On Wed, Aug 3, 2016 at 10:54 AM, Lundberg, Johannes
> <johannes at brilliantservice.co.jp> wrote:
> > Hi
> > I'm porting a project to fbsd and I have problem with this part that
> > in linux but not fbsd when fd = -1.
> > https://github.com/Cloudef/wlc/blob/master/src/session/fd.c#L80-L108
> > I get "invalid argument" from sendmsg() when setting CMSG_LEN(0).
> > Anyone have a clue how to correctly do this on fbsd?
> > Thanks!
> > Johannes
> It sounds like you're trying to send an empty cmsg. The error may
> happen because your msg_controllen field is inconsistent with your
> cmsg_len field. You're setting msg_controllen as if there were a full
> cmsg, but then cmsg_len says that there is no cmsg. Or maybe the
> error is because (just guessing) FreeBSD doesn't allow sending empty
> or undefined cmsgs. Notice that cmsg_level and cmsg_type are
> undefined in the case where fd == -1. POSIX doesn't say whether
> sendmsg supports empty cmsgs, but why bother? You could just use send
> instead of sendmsg if you're not sending a file descriptor.
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