Re: QEMU checkpoint/restore without an image?

[Leek, Jim]

Yes, that great, thanks.  I had previously tried
-drive file=dummy.qcow2,if=virtio,format=qcow2

That didn't work, but setting if=none seems to work.  I'll have to research why that is, but I'm off and running now.  Thanks.

Jim

---

From: Peter Maydell <peter.maydell@linaro.org>
Sent: Sunday, June 27, 2021 10:36 AM
To: Leek, Jim <leek2@llnl.gov>
Cc: qemu-discuss@nongnu.org <qemu-discuss@nongnu.org>
Subject: Re: QEMU checkpoint/restore without an image?

 

On Sat, 26 Jun 2021 at 22:41, Leek, Jim <leek2@llnl.gov> wrote:
>
> I'm working with VxWorks, a Real Time Operating System for embedded systems. They recently added QEMU support, and I've been trying to figure it out. (I'm fairly new to all these technologies.) I would like to checkpoint and restart the virtual machine, ie save the RAM and processor state and reload it later from exactly that point.
>
> I read up on snapshots, but those seem to require a disk image in qcow2 format. But my simulation has no disk, the program is loaded directly into RAM and run.

You need a QCOW2 image file, because that is where the data
(RAM contents, etc) is stored. But that image file doesn't
actually have to be used for anything by the system you're
emulating. This blog post I wrote ages ago:
https://urldefense.us/v3/__https://translatedcode.wordpress.com/2015/07/06/tricks-for-debugging-qemu-savevm-snapshots/__;!!G2kpM7uM-TzIFchu!n7zyZ_xSwpfWmZslCAv833b9C--yXWrKWjzVfCV6aidu2EZtV4n_S_DwYD5E-Nk$
suggests that you can create an image with
  qemu-img create -f qcow2 dummy.qcow2 32M
and then add
  -drive if=none,format=qcow2,file=dummy.qcow2
to your command line. (Ignore warnings about the drive being orphaned.)
Hopefully that still works...

-- PMM