On 03.02.26 23:47, Peter Xu wrote:
On Tue, Feb 03, 2026 at 02:04:21PM -0600, Mark Kanda wrote:
On 2/3/26 1:46 PM, Chaney, Ben wrote:
Well explained, thank you Vladimir. I wish some day we can move all at
least cpr-transfer users to local-migration and deprecate CPR if ever
possible. The uncertainty to me is cpr-exec, but I really don't know how
much mgmt is adopting cpr-exec.. cpr-reboot also looks pretty special and
may not be relevant.
The core idea (originated from Steve..) is really about fd sharing, and
it's great if we can do it in a cleaner way.
Thanks for the clarification. If that is the case then probably Vladimir's
solution is preferable. I sent some comments on the prerequisite
refactoring patch set. I'll try to review the main set soon.
My understanding is there're some special mgmt (Oracle's?) that may depend
on cpr-exec; I'm not sure how far that went in any downstream deployment.
That should be able to reuse mgmt channels too (relevant to chardev fd
sharing, perhaps?) instead of requiring e.g. all monitor ports to reconnect
to a new QEMU after migration. Said that, I always assumed re-connect is
fine, and most mgmt supports live migration so the mgmt should have that
infrastructure there already. Maybe Ben would know better.
I'm missing a lot of context here as I only became more involved in this project
recently. @Mark Kanda Can you provide any context about Steve's work before
he retired, or Oracle's usage of these features?
We (Oracle) have an internal VM manager which relies on cpr-exec, and would
like to continue supporting it.
IIUC that means QEMU upstream needs to start merging two solutions for not
only migration but also vhost, and maybe more in the future. Or we reject
Vladimir's work, but frankly I think that's indeed superior and less hacky
when without the need of the 2nd channel.
Can we try to reduce the duplicated logics between the two solutions?
For example, is it possible to rebase this series on top of Vladimir's
work, reusing logics as much as possible so that those FDs can also be
preserved via execve() and reused in the after-exec world (likely reused
not during fd open, but instead loadvm)?
I think, rebasing is not necessary, as local-fd migration (this series)
should work together with CPR, and even with CPR-exec. So Oracle can use
cpr-exec,
and simply enable backend-transfer for virtio-net/tap, and it should work, I
remember we discussed this with Steve. I didn't yet tested it, but I'll try to
add a test for such setup.
--
Best regards,
Vladimir
