Commit f48da8b14d (xen-netback: fix
unlimited guest Rx internal queue and carrier flapping) introduced a
regression.
The PV frontend in IPXE only places 4 requests on the guest Rx ring.
Since netback required at least (MAX_SKB_FRAGS + 1) slots, IPXE could
not receive any packets.
a) If GSO is not enabled on the VIF, fewer guest Rx slots are required
for the largest possible packet. Calculate the required slots
based on the maximum GSO size or the MTU.
This calculation of the number of required slots relies on
1650d5455b (xen-netback: always fully coalesce guest Rx packets)
which present in 4.0-rc1 and later.
b) Reduce the Rx stall detection to checking for at least one
available Rx request. This is fine since we're predominately
concerned with detecting interfaces which are down and thus have
zero available Rx requests.
Signed-off-by: David Vrabel <david.vrabel@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
1d5d485239