Add option to disable IPv6

[jembishop]

This PR addresses issue #2825. It adds in a new config option EPICS_PVA_ENABLE_IPV6. The intention of this is to allow completely disabling any IPv6 functionality. Right now, the current behaviour is even if you do not configure any IPv6 addresses , channels with IPv6 are still created. This causes problems as even if you do not intend to use IPv6, as you still must have this functionality in your system to run the PVA client. This is problematic in our case, as we have a containerized setup which doesn't support IPv6, which we encountered when trying to run pvws.

I don't have very much familiarity with the Phoebus codebase so I have some questions moving forward.

• I have disabled creation of IPv6 channels in ClientUDPHandler with this config option. Is there anywhere else in the codebase I should also disable IPv6 relevant things?
• Since the udp_beacon is only IPv6, currently this is just not created with this config option. Should I create it with IPv4, or is it not strictly necessary?
• Should I add in a test for this functionality in the pva/src/test folder?

[kasemir]

Looks good except for comments.

"Since the udp_beacon is only IPv6,"
It's actually IPv6 and IPv4. With IPv6 disabled, you'll need to create it as only-IPv4, not completely remove it. I think I commented on the related lines in the PR

[jembishop]

Thanks @kasemir for reviewing.
I will implement the change to create the beacon as IPv4.
I'm a bit confused, which comments are you refering too? I can't see any comments you made in the PR.

[kasemir]

This is what I see on the github page, comments within the GH 'review':

[jembishop]

Thanks. It looks like you need to submit the review? Your comments are in "Pending".
Just implemented your suggestion now, the beacon is created as IPv4 when IPv6 is disabled.

[kasemir]

Ah, submit, thanks!
Now it's just the "assert" which I'd replace with a log message or exception, since we're not generally using assert in the phoebus sources, that would be one more thing to enable/configure. Log messages and exceptions are fine.

[jembishop]

Hi, I just added some extra code to make this flag work during tests, so you can run the phoebus tests in a non ipv6 environment.

I think this PR should be good to merge now, unless you have some more review comments.

[kasemir]

Great, just waiting for the build test to pass...