Re: Is initramfs' /dev supposed to show exposed targets at Guest Boot Time?

["John L. Poole" <jlpoole56@xxxxxxxxx>]

On 1/29/2021 2:51 AM, Andy Smith wrote:
> Hi John,
>
> This looks like a xen-users question, not a xen-devel one, so I'm
> redirecting it there. Please reply on-list there.
>
> Especially if 9as it appears) you did get the guest to boot, and
> your issue is it drops to an (initramfs) prompt.
>
> I'm not sure the device will actually appear as sda3 inside the
> guest. What does "cat /proc/partitions" say form the guest's
> (initramfs) prompt?
>
> You are complicating things by trying to use LVM inside a guest.
> While that works fine, start simpler with just a simple block device
> in the guest. Export /dev/vg0/aresboot from host as xvda in guest,
> e.g.:
>
> disk = [ 'phy:/dev/vg0/aresserver,xvda,rw',
>           'phy:/dev/vg0/aresswap,xvdb,rw' ]
>
> Cheers,
> Andy
>
> On Thu, Jan 28, 2021 at 08:11:48PM -0800, John L. Poole wrote:
> > Greetings,
> >
> > I try to run Xen on low energy platforms.  I've previously been here about
> > an Intal Atom which died
> > just after the 3 year warranty expired.  So I'm trying AMD's laptop Ryzen.
> > I think I've been using Xen
> > for 8 years.
> >
> > I have Debian (Linux snuc 4.19.0-13-amd64 #1 SMP Debian 4.19.160-2
> > (2020-11-28) x86_64 GNU/Linux)
> > running on a new SimplyNuC:  Aspen PN50 R7 4800U with a AMD Ryzen™ 4000
> > Renoir mobile processor.
> >
> > (I tried to run Xen from the factory installed Ubuntu and ran into the same
> > problem below, so I
> > thought I ought to use Debian in case Ubuntu had a shortcoming re: lvm)
> >
> > I created volumes with lvm, i.e. /dev/vg0/aresboot, /dev/vg0/aresswap,
> > /dev/vg0/aresserver
> > which are to be exposed to the Gentoo environment as sda1, sda2, and sda3.
> > My Gentoo
> > /etc/fstab accordingly has sda1,2, & 3 specified.  My problem occurs, I
> > think, before my Gentoo
> > kernel even has a chance to perform its initialization.
> >
> > I am trying to create a Gentoo VM and successfully built a kernel and
> > initramfs in a chrooted
> > environment within /dev/vg0/aresserver.  I've successfully done this before
> > on
> > other platforms; however, my attempt now is on this tiny, but powerful and
> > efficient, SimplyNUC.
> >
> > And, I think this may be my first time using LVM partitions exclusively
> > rather than standard fsdisk partitions.
> >
> > When I try to "xl create ares.conf -c", the Gentoo kernel is unable to see
> > the labeled "sda3"
> > [target is Debian's /dev/vg0/aresserver].
> >
> > I'm not new Xen and have not had this kind of problem before, but I also
> > don't think I staged
> > my guests completely on lvm partitions.  I'm thinking there is a problem
> > between the
> > Xen Kernel code and Gentoo's kernel and I think the problem may be on the
> > Gentoo side.
> >
> > The version of lvm on Debian is: 2.03.02(2)
> > The version of lvm [lvm2] on Gentoo is: 2.02.187-r2
> >
> > (Would a lvm 2.02 be unable to read a 2.03??)
> >
> > My question now is: when my Gentoo initramfs can't find the partition and I
> > enter its shell, should I
> > be seeing the exposed partition, e.g. "sda3", under /dev?  I think so.
> >
> > None of the names I specify, e.g. "sda3", appear under the /dev listing (see
> > pastebin below).
> >
> > A sample configuration for the disk (just 1 target used to debug this
> > problem) is:
> >
> > disk = ['format=raw, vdev=sda3, access=rw,
> > target=/dev/mapper/vg0-aresserver']
> >
> > I have tried specifying root as "sda3" -- the name that the target should
> > appear as in the guest
> > environment as well as the full path from the Dom0 environment (above).
> >
> > I'm guessing my problem is an initramfs and/or kernel issue in Gentoo: being
> > unable to
> > read an lvm partition.  Note, when I compiled, I used genkernel as follows:
> >
> >       genkernel --menuconfig --lvm --mdadm all
> >
> > and my xen configuration has:
> >
> >       root=/dev/vg0/aresserver dolvm  domdadm
> >
> > (root=/dev/sda3 and root=sda3 do not work either)
> >
> > Before I approach Gentoo developers, I wanted to learn from the Xen gurus
> > that my assumption that the
> > initramfs /dev listing is the correct assay to determine if initramfs and/or
> > the kernel are
> > able to see the Debian lvm partitions.
> >
> > Here is a pastebin of my create session and listing of /dev from within
> > initramfs shell: https://pastebin.com/juybx5gU
> >
> > So, should I be seeing "sda3" when I list /dev?
> >
> > Thank you.
> > --
> > Email Rider
> >
> > John Laurence Poole
Hi Andy,

Answer to your question:

     rescueshell / # cat /proc/partitions
     rescueshell / #

Since writing, I've learned of problems on the Gentoo side with lvm [lvm2].

Specifically, the Gentoo lvm2 package maintainer warns:
*[**lvm2-2.03 ] Needs LOTS of testing, broke boot on my laptop in early 
attempts,
maybe needs matching genkernel work?*

https://packages.gentoo.org/packages/sys-fs/lvm2

In my original posting, I've noted Debian is running lvm 2.03.02(2)
whereas my Gentoo guest is has lvm 2.02.187-r2  and I used genkernel.

Another recent posting on the Gentoo forums reports a similar
problem where the author "can't mount the root partition when booting.":

https://forums.gentoo.org/viewtopic-t-1128130-highlight-lvm2.html?sid=30c4ec50ca3e7d53f56cc098d7c0acb2

I guess lvm and Gentoo and Xen is asking too much at this time, I'll have to
retreat and not use lvm for the base system.

Thank you,

John