• Paul Durrant's avatar
    xen-netback: support dynamic unbind/bind · 9476654b
    Paul Durrant authored
    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: default avatarPaul Durrant <pdurrant@amazon.com>
    Reviewed-by: default avatarWei Liu <wei.liu@kernel.org>
    Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
    9476654b
interface.c 20.6 KB