Paul Brook wrote:
>> Paul Brook wrote:
>>>> A major reason for this deadlock could likely be removed by shutting
>>>> down the tap (if peered) or dropping packets in user space (in case of
>>>> vlan) when a NIC is stopped or otherwise shut down. Currently most (if
>>>> not all) NIC models seem to signal both "queue full" and "RX disabled"
>>>> via !can_receive().
>>> No. A disabled device should return true from can_recieve, then discard
>>> the packets in its receive callback. Failure to do so is a bug in the
>>> device. It looks like the virtio-net device may be buggy.
>> That's not a virtio-only issue. In fact, we ran into this over pcnet,
>> and a quick check of other popular PCI NIC models (except for rtl8139)
>> revealed the same picture: They only report can_receive if their
>> receiver unit is up and ready (some also include the queue state, but
>> that's an "add-on").
>
> If so these are also buggy.
>
>> I think it's clear why: "can_receive" strongly suggests that a suspended
>> receiver should make the model return false. If we want to keep this
>> handler, it should be refactored to something like "queue_full".
>
> I don't see a need to refactor anything. You just need to fix the devices
> that incorrectly return false when their RX engine is disabled.
"can_receive" is a misleading name. NIC model developers will continue
to make mistakes when implementing this function. And I don't think we
want such implementations all around:
static int rtl8139_can_receive(VLANClientState *nc)
{
RTL8139State *s = DO_UPCAST(NICState, nc, nc)->opaque;
int avail;
/* Receive (drop) packets if card is disabled. */
if (!s->clock_enabled)
return 1;
if (!rtl8139_receiver_enabled(s))
return 1;
if (rtl8139_cp_receiver_enabled(s)) {
/* ??? Flow control not implemented in c+ mode.
This is a hack to work around slirp deficiencies anyway. */
return 1;
} else {
avail = MOD2(s->RxBufferSize + s->RxBufPtr - s->RxBufAddr,
s->RxBufferSize);
return (avail == 0 || avail >= 1514);
}
}
Jan
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
