Re: [PATCH v4 0/8] Live update: tap and vhost

[Peter Xu <peterx@redhat.com>]

On Thu, Jan 29, 2026 at 04:58:41PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> On 28.01.26 23:39, Ben Chaney wrote:
> > Tap and vhost devices can be preserved during cpr-transfer using
> > traditional live migration methods, wherein the management layer
> > creates new interfaces for the target and fiddles with 'ip link'
> > to deactivate the old interface and activate the new.
> > 
> > However, CPR can simply send the file descriptors to new QEMU,
> > with no special management actions required.  The user enables
> > this behavior by specifing '-netdev tap,cpr=on'.  The default
> > is cpr=off.
> > 
> > Signed-off-by: Ben Chaney <bchaney@akamai.com>
> Hi!
> 
> I'd like to note again, that I'mvworking on an alternative solution for live-updating
> virtio-net+TAP, passing FDs through unix domain socket, which:
> 
> 1. Doesn't require second migration channel
> 2. Doesn't use CPR: the whole TAP state, including negotiated parameters
> and opened FD are natively passed as usual migration state structure.
> (look here: https://lore.kernel.org/qemu-devel/20251030203116.870742-7-vsementsov@yandex-team.ru/ )
> 3. Still should be compatible with CPR, and may be used in context of CPR-update
> 
> The latest version was
> 
> [PATCH v9 0/8] virtio-net: live-TAP local migration
> https://lore.kernel.org/qemu-devel/20251030203116.870742-1-vsementsov@yandex-team.ru/
> 
> and I plan to post v10 soon.

Yes, thanks for re-raising this.  If we have similar features being
proposed, we should always discuss whether we should stick with one of them
if that'll work for all.

IIUC Vladimir's solution looks indeed superior in that it has less
constraints, and also works for CPR mode.

Thanks,

-- 
Peter Xu