[ipv6] RFR: 8223532: Don't try creating IPv4 sockets in NetworkInterface.c if IPv4 is not supported

[Daniel Fuchs]

Hi Arthur,

The idea looks reasonable to me - I believe the changes in
NetworkInterface.c should be OK.

However - I don't think the changes in net_util.c::DEF_JNI_OnLoad
are acceptable.
I'll question whether this is the right place to bail
out. I agree it would be nice to have some diagnostic
that tells us that the native library is non-functioning
because both IPv4 & IPv6 where not available, but I'd rather
have this check at the place where the code actually tries
to e.g. open an IP/TCP socket, and where throwing a regular exception
with a better detailed message is possible, rather than
having the VM fail to start with some cryptic UnsatisfiedLinkError.

best regards,

-- daniel

On 08/05/2019 06:52, Arthur Eubanks wrote:
> Bug: https://bugs.openjdk.java.net/browse/JDK-8223532
> Webrev: http://cr.openjdk.java.net/~aeubanks/8223532/webrev.00/
> 
> There are a couple of functions in 
> src/java.base/unix/native/libnet/NetworkInterface.c which try to create 
> IPv4 sockets, then check if errno is EPROTONOSUPPORT. If errno is 
> EPROTONOSUPPORT, then IPv6 is tried, else it immediately bails.
> 
> We have a kernel that returns EAFNOSUPPORT when IPv4 is disabled and 
> there is an attempt to create an AF_INET socket.
> 
> Rather than adding a check for EAFNOSUPPORT, which seems too specific, 
> just don't bother trying to create an IPv4 socket if IPv4 is not 
> available. This uses ipv4_available(), introduced in 
> http://hg.openjdk.java.net/jdk/jdk/rev/22323f20401b.
> 
> Since previously the code assumed that we have at least IPv4, now when 
> initializing ipv4/6_available(), make sure that at least one of them is 
> available, or else bail. One problem I have with this is that the error 
> message when neither is present is not descriptive:
> Error occurred during initialization of boot layer
> java.lang.UnsatisfiedLinkError: unsupported JNI version 0xFFFFFFFF 
> required by path/to/jdk/build/jdk/lib/libnet.so