netdev - Force mavtap interfaces up

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Message-ID: <116c870676ecab331ec3c76aaec7bf0f@assyoma.it>
Date:   Mon, 02 May 2022 18:30:10 +0200
From:   Gionatan Danti <g.danti@...yoma.it>
To:     netdev@...r.kernel.org
Subject: Force mavtap interfaces up

Dear list,
I would like to ask if, and how, it is possible to force a macvtap 
interface up even when the underlying physical device has no link 
(reporting NO-CARRIER).

 From my understanding, I can do that via something as "ip link set 
macvtap0 protodown off". And it works, indeed. However, if the 
underlying physical device is plugged & unplugged again, the macvtap0 
interface goes down with it; to restore it, I need to re-run the above 
"protodown off" command.

Does a method exists to always force one or more macvtap interfaces up, 
regardless the physical link status?

Full disclosure: I am trying to use macvtap rather than plain bridge for 
a KVM host and I stumbled across the behavior described above. If the 
physical interface is disconnected, the guests lose connection with each 
other. With a classical bridge setup, disconnecting the physical 
interface only interrupt communication with outer guest/hosts (but 
internal traffic is preserved).

Regards.

-- 
Danti Gionatan
Supporto Tecnico
Assyoma S.r.l. - www.assyoma.it
email: g.danti@...yoma.it - info@...yoma.it
GPG public key ID: FF5F32A8