[BuildStream] Buildbox-casd logs

[Benjamin Schubert <contact benschubert me>]

Hey everyone,

TLDR: I propose to store Buildbox-casd logs in

'XDG_CACHE_HOME/buildstream/buildbox-casd.log' with WARNING severity and

expose the severity through an environment variable.

Now that we are using Buildbox-casd as a local CAS server, there are some

times where we encounter a problem in it and debugging those problems is

hard, since currently, we don't do anything with the its output.

I think we should save Buildbox-casd output. However, contrary to other host

tools we use currently, Buildbox-casd is not in a plugin context, but is a

child to the main BuildStream process. That means we cannot save the output

in a specific element directory.

I therefore would propose to save its output to

'XDG_CONFIG_HOME/buildstream/buildbox-casd.log'. We would always append to

this file, and not erase it.

We might also want to be able to have more logs than just warnings or errors.

I want to therefore introduce a 'BST_BUILDBOXCASD_LOG' environment variable,

that would be used to set the verbosity of those logs, using WARNING as a

default.

Does anyone has any objection around this plan or would like to suggest

better alternatives?

Thanks!

Ben