New Gentoo in qemu: Format vda as partition instead of disk

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

Hi,

I'm installing a new gentoo guest on a gentoo host. I want it to be really simple, meaning one partition if I can manage it.

I have an lvm volume on the host as the disk storage. It shows up in the guest as /dev/vda.

It would be awesome if I could simply format that as ext4 and go, rather than formatting it as a separate disk.

The host is UEFI boot, if it's simple to do this with the guest then I'm fine with that. Only then I'll need a separate partition, which blows my whole plan out of the water unless I can allocate another small LVM volume just for that?

Thanks.

NeddySeagoon · Posted: Fri Jan 22, 2016 8:23 pm Post subject:

1clue,

If you format the whole volume, there is nowhere for a partition table.
That upsets BIOS and bootloaders.

With EFI, it might work for booting but you would be stuck with VFAT
VFAT does not support symlinks, *NIX permissions and so on so you could not install *NIX there.

In my KVMs I donate a logical volume from the host as storage for the KVM then use it as a disk.
There is no host file system on the logical volume, so overhead is minimal.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

That's not the answer I was hoping for but it is the one I expected. Thanks.

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

So with a uefi host, is it better to stick with uefi guests too?

szatox · Advocate Joined: 27 Aug 2013 Posts: 3135

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

I might play with this direct linux boot.

I just wish I could have a partition that could be mounted by the host as well as the guest.

And another thing, I thought Gentoo's minimal iso would support virtio drivers by now.

szatox · Advocate Joined: 27 Aug 2013 Posts: 3135

Yes, you can mount it at your host. In fact it's a part of the building process, which means there is no use for minimal iso at all.
You can build everything with your host, copy it into a drive image (yes, yes, just formatted, without partition table), and then _JUST_ boot the VM with
-kernel <path to kernel> [-initrd <path to initramfs>] -drive file=<path to disk image>,cache=none,if=virtio
Heh, gotta get myself together and finally write a script for building this stuff. Preferably a usable one this time, rather than a prototype :lol:

Ah, there is also virtfs available in qemu. Never tried it, but it looks promising in term of your desire to mount some things at guest and host.

NeddySeagoon · Posted: Sat Jan 23, 2016 10:50 am Post subject:

1clue,

At the host, a partitioned logical volume looks like a partitioned drive.
You can mount the individual partitions with the offset= parameter to mount.

You can probably use losetup to scan the host logical volume for partitions, then mount them.
Warning - losetup did not work with GPT last time I tried.
_________________
Regards,

NeddySeagoon

Computer users fall into two groups:-
those that do backups
those that have never had a hard drive fail.

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

Hmm. I'll still need a kernel because one of the guests will be a linux advanced router. Another will be pfSense. They'll be nested.

It occurs to me that since my /usr/src is a separate volume I can share it across vms. Contemplating having portage directories be shared too. I'll need to do some cleanup.

This is really interesting. I've never colored outside the lines with kvm before.

TigerJr · Guru Joined: 19 Jun 2007 Posts: 540

szatox · Advocate Joined: 27 Aug 2013 Posts: 3135

NeddySeagoon · Posted: Sun Jan 24, 2016 10:28 am Post subject:

szatox,

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

My guests will not have the same kernel or the same @world as the host. That's why I have VMs instead of everything on one box.

I love the idea of sharing the large volume bits if I can, but not if I have to have a VM exactly the same as the host. I'm perfectly fine having one /usr/src, I'm perfectly fine with a unified /usr/portage, I'm definitely interested in sharing anything that will always be the same on any up-to-date Gentoo box. I will need to keep each compiled kernel and each @world and USEs separate.

I've been using VMware and Parallels in my job for about 15 years now. I've occasionally used KVM also, both personally and with my job. But I've never used LVM storage for it, and I've never tried anything fancy like what we're talking about here.

I was going to try to set up the host with distcc and have the guests just borrow the host cores, so to speak. Still think that might be a good way to go, all things considered.

This is all pretty heavy stuff for me, I'm going to need to digest it and plan things out. Again.

Thanks.

TigerJr · Guru Joined: 19 Jun 2007 Posts: 540

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

What's the best way to have a partition open r/w in both the host and the guest simultaneously?

VMware just doesn't support this, period. Parallels lets you share drives, folders whatever. Do I need to set up an nfs share or can I do it with something easier and faster?

Thanks.

szatox · Advocate Joined: 27 Aug 2013 Posts: 3135

3 ways:
1) use clustered FS that allows you actively using a single volumes from 2 machines at the same time
2) use file-level protocol like NFS or virtfs
3) dont-do-that-for-anything-of-any-importance-at-all flush buffers at guest before you acess from host, flush buffers at host before you access from guest.

TigerJr · Guru Joined: 19 Jun 2007 Posts: 540

Ant P. · Watchman Joined: 18 Apr 2009 Posts: 6920

1clue · Advocate Joined: 05 Feb 2006 Posts: 2569

The 9p option seems to be what I'm after. Thanks.

Gotta recompile my host kernel for this, and had to do it anyway because of new kernel with things I want.

Thanks again everyone!