Create directory in the guest to mount --rodir in

[bjackman]

Another case where what I want seems simple enough, but I'm not sure what the behaviour/UX should be.

I don't like using my host rootfs for testing (it changes too much) so I normally boot a minimal guest in virtme-ng and then pass stuff I wanna run in there in via --rodir or --rwdir. I usually just use /mnt as the guest directory for that.

The minor annoyance comes when I wanna pass multiple directories in that way: the target directory needs to exist in the guest but if I've already used /mnt for one directory I can't use it again.

I think the best ways I can see to solve that would be:

1. Just have virtme-init create the target directory unconditionally.
2. Add some optional variant like --rwdir-create/--rodir-create that does this.

Option 1 seems like it might cause some surprise since that's not how mount or /etc/fstab works. If it only created 1 level of directory (mkdir rather than mkdir -p) that might help mitigate the worst sources of confusion. Option 2 seems easiest to reason about but it's kinda annoying to create new "configuration surface" like that. Any other options / other thoughts?

[bjackman]

(Deleted a nonsense comment. I was looking at the old virtme init code instead of virtme_ng_init when I wrote the above. So I got all confused, but I think after all I was right that this isn't supported).

Example command:

 unshare -r vng --verbose --root ~/src/limmat-kernel/mkosi-rootfs/image/ --user root --rwdir=/mnt/kst=$PWD/tools/testing/selftests/kselftest_install --overlay-rwdir=/mnt/kst -- "cd /mnt/kst/mm; ./run_vmtests.sh -t mmap

In this caser init fails with: mount: /mnt/kst: mount point does not exist.