adding rsockets support into JDK

[Chris Hegarty]

Lucy,

Thank you for the update. I’m still reviewing, but just on one point
below.

> On 20 Nov 2018, at 04:06, Lu, Yingqi <yingqi.lu at intel.com> wrote:
> 
> Hi Chris,
> 
> Thank you for your quick feedback. I have uploaded version 18 of the patch at http://cr.openjdk.java.net/~ylu/8195160.18/
> 
> In this version, I have changed following items according to your suggestions:
> 
> ...
> 4. In terms of adding -Djava.net.preferIPv4Stack=true for all the tests, I tested couple test cases without the flag and they return error. I think the reason is that Java uses IPv6 by default if kernel supports it. However rsocket does not support IPv4-mapped addresses. That is the reason why the flag is needed. Please let me know if there is anything I miss here though.

Maybe I'm missing something, but if the rsocket implementation on Linux
does not support IPv6 then why not just set the domain to AF_INET in the
code. That is one implication of what is being achieved with
`java.net.preferIPv4Stack `. For example in
src/jdk.net/linux/native/libextnet/LinuxRdmaSocketImpl.c

 JNIEXPORT void JNICALL
 Java_jdk_internal_net_rdma_LinuxRdmaSocketImpl_rdmaSocketCreate(JNIEnv *env, jobject this,
                                            jboolean stream, jobject impl) {
     jobject fdObj, ssObj;
     int fd;
     int type = (stream ? SOCK_STREAM : SOCK_DGRAM);
     int domain = ipv6_available() ? AF_INET6 : AF_INET;  // <<< HERE

     ...
     if ((fd = rs_socket(domain, type, 0)) == -1) {
     ...
 }

Or does IPv6 work ok, just not for IPv4-mapped addresses? I'm trying to
understand if IP protocol-specific configuration should be exposed in
the factories for creating IP protocol-specific sockets and channels,
similar to `DatagramChannel::open​(ProtocolFamily)`.

-Chris.