ch-remote: Fix crash when run with no subcommand

[arachsys]

ch-remote crashes when run with --api-socket but no subcommand:

$ target/release/ch-remote --api-socket /tmp/api
thread 'main' panicked at src/bin/ch-remote.rs:509:14:
internal error: entered unreachable code

Use clap::Command::subcommand_required(true) to yield a more friendly error in this case.

[arachsys]

Locally, I added arg_required_else_help(true) to both cloud-hypervisor and ch-remote for better interactive convenience, but I didn't propose it in this patch as I'm not sure how you feel about that behaviour vs a 'missing subcommand' error from ch-remote?

[rbradford]

Thank you so much for finding this and working on a fix. I think I .arg_required_else_help() makes sense for ch-remote and the cloud-hypervisor binary (probably also the vhost daemons that are in tree.) Running cloud-hypervisor with no arguments isn't useful (expect perhaps in the dbus case? @brkp ?).

[arachsys]

Thank you so much for finding this and working on a fix. I think I .arg_required_else_help() makes sense for ch-remote and the cloud-hypervisor binary (probably also the vhost daemons that are in tree.) Running cloud-hypervisor with no arguments isn't useful (expect perhaps in the dbus case? @brkp ?).

Great, thanks! Very happy to update to add arg_required_else_help() in each place as well. I hadn't spotted vhost_user_*/src/main.rs, but looking at them, they do each have a backend argument that's required, so emitting help when run 'bare' does sound more helpful for them too.

[arachsys]

Looks like the x86-64 (garm-jammy-amd, musl) test failed because of wget timing out. (There were quite a few strange network problems on GitHub last night: I saw some other CI stuff failing randomly on checkouts too.) I'm not sure if there's a way I can trigger it to re-run?

[brkp]

Running cloud-hypervisor with no arguments isn't useful (expect perhaps in the dbus case?).

Yeah, this applies to the D-Bus API as well, it is not started if no relevant arguments are passed to cloud-hypervisor.