>Number:         33676
>Category:       kern
>Synopsis:       socket(2) returns incorrect errno if domain is not supported
>Confidential:   no
>Severity:       non-critical
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Fri Jun 09 14:30:00 +0000 2006
>Originator:     Valeriy E. Ushakov
>Release:        current as of 2006-06-09
>Organization:
>Environment:
>Description:
socket(2) incorrectly sets errno to EPROTONOSUPPORT
if the protocol family is not supported.

To quote http://www.fefe.de/libowfat/changes-0.23.txt

    work around freebsd 5.4 brokenness (if you don't have IPv6 in the
    kernel, socket(PF_INET6,SOCK_STREAM,0) returns EPROTONOSUPPORT
    instead of EPFNOSUPPORT, which basically says "yeah, I know IPv6,
    but TCP?  never heard of it")


SUS says <http://www.opengroup.org/onlinepubs/007908799/xns/socket.html>
that socket(2) should return EAFNOSUPPORT in that case.

There's a complication in that POSIX doesn't have
PF_* values (it uses AF_* instead).  We do have PF_*
so returning EPFNOSUPPORT would be a logical choice,
but as it's != EAFNOSUPPORT, it seems impossible to be
both posixly correct and internally consistent.

>How-To-Repeat:
Try to start in-tree postfix on a custom kernel w/out IPv6 support.
potfix is compiled with IPv6 support enabled, so it checks if IPv6
support is present in the kernel by creating a PF_INET6 socket
it expects EAFNOSUPPORT to indicate lack IPv6 support.
It gets EPROTONOSUPPORT instead and treats it as a fatal error.

>Fix: