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SubjectRe: [PATCH net-next] xen-netback: support dynamic unbind/bind
From: Paul Durrant <>
Date: Mon, 23 Dec 2019 09:59:23 +0000

> By re-attaching RX, TX, and CTL rings during connect() rather than
> assuming they are freshly allocated (i.e. assuming the counters are zero),
> and avoiding forcing state to Closed in netback_remove() it is possible
> for vif instances to be unbound and re-bound from and to (respectively) a
> running guest.
> Dynamic unbind/bind is a highly useful feature for a backend module as it
> allows it to be unloaded and re-loaded (i.e. updated) without requiring
> domUs to be halted.
> This has been tested by running iperf as a server in the test VM and
> then running a client against it in a continuous loop, whilst also
> running:
> while true;
> do echo vif-$DOMID-$VIF >unbind;
> echo down;
> rmmod xen-netback;
> echo unloaded;
> modprobe xen-netback;
> cd $(pwd);
> brctl addif xenbr0 vif$DOMID.$VIF;
> ip link set vif$DOMID.$VIF up;
> echo up;
> sleep 5;
> done
> in dom0 from /sys/bus/xen-backend/drivers/vif to continuously unbind,
> unload, re-load, re-bind and re-plumb the backend.
> Clearly a performance drop was seen but no TCP connection resets were
> observed during this test and moreover a parallel SSH connection into the
> guest remained perfectly usable throughout.
> Signed-off-by: Paul Durrant <>

Applied, thank you.

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