Add send2vsock to send systemd journal from a guest to the host

[kzys]

Signed-off-by: Kazuyoshi Kato [email protected]

Issue #, if available:

#276

Description of changes:

This PR is still work-in-progress. Early feedback is welcome!

Basically I want to run journalctl -f | send2vsock as a systemd unit. systemd can forward logs to syslogd, but supporting a remote syslogd location is not supported and using a mini daemon is recommended instead (see systemd/systemd#7170).

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[sipsma]

Think the basic idea here is good, just some more things we'll need to figure out:

1. Users are going to need a way to consume these logs
2. We'll need to make sure that the vsock port used by this doesn't conflict with the vsock ports used internally for apis/stdio.

One initial thought I had was to run this code as a semi-privileged "sidecar" container (we could vend the container definition in some utility library in this repo). That solves both of the above problems pretty cleanly but has a pretty big disadvantage in that we won't be able to get the logs until the container has actually started, which misses a lot of problems that can happen during boot+agent start.

My only other idea is to add parameters to the CreateVM api that define "reserved" vsock streams, which will allow us to reserve port numbers and tell users where to find the unix socket on which they can listen to services from within their VM, such as this journal forwarder. Curious to hear others' thoughts.

[kzys]

I'm going to close the PR for now. We will check the overall performance first instead of just avoid using the console device.