docs: A tip on using rootfs

[bjackman]

With this trick I've been able to use rootfs directories built using mkosi, without needing root on the host system.

I guess people who are running this via Docker etc effectively already have this in place.

[danobi]

What error do you get otherwise? I'm trying to get a sense of whether or not vmtest could automatically do this.

Btw, might be good to hint about building images with mkosi. IMO usually useful to leave an example when leaving hints

[bjackman]

What error do you get otherwise?

In my case the error is: mount: /proc: must be superuser to use mount. I guess this is because the mount is setuid but not to the root user. i did briefly try mounting root with nosuid, it didn't work but that could easily just be I did something wrong or there could be some other similar workarond.

I'm trying to get a sense of whether or not vmtest could automatically do this.

Yeah I was also thinking about this, like maybe there would be some benefit to having vmtest itself remain in the original namespace and just running QEMU in the namespace. It definitely could the question is just about should I think.

I think it would probably have to be configurable, otherwise it could cause pain for someone who wants direct control over the rootfs? I dunno though I might just be creating speculative complexity with that statement.

Btw, might be good to hint about building images with mkosi. IMO usually useful to leave an example when leaving hints

I didn't add it coz a) I don't think I can provide instructions that I'm confident will work on multiple distros and b) I think (?) mkosi is a bit of an overpowered tool for this problem, I am using it because I also want to be able to build the same thing into a disk image complete with bootloader etc for booting on HW.

Anyway, I can definitely dump what I know and an example config :) I'll do it in a separate PR to decouple.

[bjackman]

I'll do it in a separate PR to decouple.

On 2nd thoughts, those tips aren't useful without the user namesapce so no point in decoupling.

I think (?) mkosi is a bit of an overpowered tool for this problem

Yeah, I tried an experiment and it seems an OCI container image works fine for this. I think those are incomplete systems, like I don't think they have a full systemd etc, but I guess that's not an issue for vmtest.

[bjackman]

CC @daandemeyer :), maybe he can provide extra tips / point out potential issues

[danobi]

sweet! great doc

[daandemeyer]

The latest virtiofsd will have uid mapping built in without needing user namespaces. vmtest can use that so you don't have to mess around with namespaces since I vaguely remember reading about vmtest using virtiofsd as a library.

[danobi]

The latest virtiofsd will have uid mapping built in without needing user namespaces. vmtest can use that so you don't have to mess around with namespaces since I vaguely remember reading about vmtest using virtiofsd as a library.

Yep, that's being worked on in #88. Should remember to delete the hint when we merge it