RFC: Initial vsock stream support

[gkelly]

What does this PR do?

Adds initial vsock stream socket support to glommio. This is just to start a discussion of the approach, and is NOT ready to land.

Motivation

I am working on high-throughput vsock applications running inside of hypervisors and am evaluating glommio as a potential IO framework.

This implementation is based heavily off of the tcp_socket implementation.

Additional Notes

This is a draft PR, it is not yet ready to merge. It is missing the following:

• Decide on how to treat SOCK_DGRAM sockets. I'm open to feedback here, but given how similar a STREAM and DGRAM socket behave under vsock I'm tempted to genericize the pieces across the SOCK_ type.
• All of the missing documentation the linter's unhappy about.
• Make the vsock example more complete, it's currently just an echo server to prove it works.
• Tests.
• Benchmarks.

[glommer]

Thanks @gkelly !

I am taking a look at this now

[glommer]

I don't have a lot of comments, to be honest - aside from the lack of documentations on public functions that I am sure you will fix eventually.

The implementation is quite straightforward, and I think the abstraction is the right one (having a generic socket type would be overkill IMHO, so a new class for VSock makes sense).

The example application is neat and simple. The only thing that I'd like to see more is testing and benchmarks, but I realize this can get a bit non trivial with vsock and its setup.

What are the milestones you have in mind before considering ready to merge?

[glommer]

Okay, I see now that you did add a bunch of things to the list of milestones - including testing and benchmarks.

You already noticed the docs as well, so the only open comment is on how generic this should be.

I don't have a preference to be honest, on the implementation. In terms of API, I like the direction you are taking with a special case top level class, instead of making the socket type a parameter.

My reason for that is that in practice, almost everything is either a standard tcp or dgram socket. Any approach that parametrizes a socket puts the burden of reasoning on people using the standard socket types.