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Re: [Xen-devel] booting from HVM (?pv?)



On 06/25/2013 11:57 AM, AL13N wrote:
On 06/25/2013 11:47 AM, AL13N wrote:
On Mon, Jun 24, 2013 at 9:21 PM, AL13N <alien@xxxxxxxx> wrote:
Hi,

I'm the Mageia XEN packager and during QA, we stumbled into a problem.

in fact, we wanted to test Mageia 3 installation on a HVM.

so, we had a sparse image and a iso file:

[ 'file:/opt/testhvm.img,sda,w',
'file:/opt/mageialive.iso,hdb:cdrom,r'
]

the live booted, and was able to install to disk, but it never seemed
to
boot
after the install... (for some reason)

in the end, this "worked" when we changed to:

[ 'file:/opt/testhvm.img,xvda,w', 'file:/opt/testhvm.img,sda,w' ]

apparently 'xvda' to get grub to boot the kernel; and 'sda' so that it
could
start...

My HVM Linux config files have 'hda' instead of 'sda' -- can you try
that instead?

Normally what happens is that qemu begins by exposing the hda device
to the guest, to boot via grub; but when the Xen PV drivers in the
Linux kernel come up, they write to a magic port which causes the
physical hda device to disappear.  I *think* then that the Xen PV
drivers actually take over that major/minor, so that further reads and
writes to the hda go through the PV protocol instead.

All of this might get mixed up if you're using sda instead.

   -George



well, hda is what we tried first, but we couldn't see the disk from the
live system with hda. only sda seemed to work for that...

When you say, "we couldn't see the disk from the live system", you're
talking about booting from the live CD?

If post-install you try 'hda' and it boots (after changing the grub and
/etc/fstab if necessary), then I would suspect that there's a problem
with your live CD kernel.  Do you use a different kernel image, and/or
are the modules for the Xen PV devices not included?

what i mean is:

1st try was using hda en hdb:cdrom with an iso and boot=dc

Hmm, I think we normally use hdc for the cdrom instead of hdb. hda and hdb would be on the same controller, I think; so it's probably not possible to unplug hda without also unplugging hdb. In that case, having the PV drivers loaded could actually make things worse: if they successfully unplug hda, then they lose the cdrom; if they don't, then the PV drivers may be in a weird state where they've grabbed the hda device but aren't able to provide access to the disk anymore.


this booted from the livecd, but the disk was not visible, even though
xenblk_front was loaded (does hvm use a different module for emulation?
there were some ide modules loaded as well).

this is one thing we wanted to get right when having Mageia to be
xen-ready (ie: installable on HVM from iso)

Absolutely -- I'm just exploring configuration / guest kernel setups that can be tweaked, particularly since at the moment we're pretty much locked down for 4.3, so any changes won't be in a public release until 4.4 in (probably) 6 months' time.


We'll try using hda postinstall...


PS: one weird thing that i saw in the log files, was a message about
stripping tap from device, which was odd, since file:/... was specified
and not tap:aio:... (and Mageia 3 doesn't have a specific -xen kernel, nor
a blktap-dkms...)

If you could post the exact message, we could find out where the warning was coming from and see if it's something to worry about.

 -George

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