Re: [PATCH v7 3/3] net/virtio: support GUEST ANNOUNCE

["Wang, Xiao W" <xiao.w.wang@intel.com>]

> From: Maxime Coquelin [mailto:maxime.coquelin@redhat.com]
> On 01/09/2018 03:26 PM, Xiao Wang wrote:
> > When live migration is done, for the backup VM, either the virtio
> > frontend or the vhost backend needs to send out gratuitous RARP packet
> > to announce its new network location.
> >
> > This patch enables VIRTIO_NET_F_GUEST_ANNOUNCE feature to support
> live
> > migration scenario where the vhost backend doesn't have the ability to
> > generate RARP packet.
> >
> > Brief introduction of the work flow:
> > 1. QEMU finishes live migration, pokes the backup VM with an interrupt.
> > 2. Virtio interrupt handler reads out the interrupt status value, and
> >     realizes it needs to send out RARP packet to announce its location.
> > 3. Pause device to stop worker thread touching the queues.
> > 4. Inject a RARP packet into a Tx Queue.
> > 5. Ack the interrupt via control queue.
> > 6. Resume device to continue packet processing.
> >
> > Signed-off-by: Xiao Wang <xiao.w.wang@intel.com>
> > ---
> >   drivers/net/virtio/virtio_ethdev.c | 95
> +++++++++++++++++++++++++++++++++++++-
> >   drivers/net/virtio/virtio_ethdev.h |  1 +
> >   drivers/net/virtio/virtqueue.h     | 11 +++++
> >   3 files changed, 105 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/net/virtio/virtio_ethdev.c
> b/drivers/net/virtio/virtio_ethdev.c
> > index e8ff1e449..9606df514 100644
> > --- a/drivers/net/virtio/virtio_ethdev.c
> > +++ b/drivers/net/virtio/virtio_ethdev.c
> > @@ -19,6 +19,8 @@
> >   #include <rte_pci.h>
> >   #include <rte_bus_pci.h>
> >   #include <rte_ether.h>
> > +#include <rte_ip.h>
> > +#include <rte_arp.h>
> >   #include <rte_common.h>
> >   #include <rte_errno.h>
> >   #include <rte_cpuflags.h>
> > @@ -78,6 +80,11 @@ static int virtio_dev_queue_stats_mapping_set(
> >   	uint8_t stat_idx,
> >   	uint8_t is_rx);
> >
> > +static int make_rarp_packet(struct rte_mbuf *rarp_mbuf,
> > +		const struct ether_addr *mac);
> > +static void virtio_notify_peers(struct rte_eth_dev *dev);
> > +static void virtio_ack_link_announce(struct rte_eth_dev *dev);
> > +
> >   /*
> >    * The set of PCI devices this driver supports
> >    */
> > @@ -1272,9 +1279,89 @@ virtio_inject_pkts(struct rte_eth_dev *dev, struct
> rte_mbuf **tx_pkts,
> >   	return ret;
> >   }
> >
> > +#define RARP_PKT_SIZE	64
> > +static int
> > +make_rarp_packet(struct rte_mbuf *rarp_mbuf, const struct ether_addr
> *mac)
> > +{
> > +	struct ether_hdr *eth_hdr;
> > +	struct arp_hdr *rarp;
> > +
> > +	if (rarp_mbuf->buf_len < RARP_PKT_SIZE) {
> > +		PMD_DRV_LOG(ERR, "mbuf size too small %u (< %d)",
> > +				rarp_mbuf->buf_len, RARP_PKT_SIZE);
> > +		return -1;
> > +	}
> > +
> > +	/* Ethernet header. */
> > +	eth_hdr = rte_pktmbuf_mtod(rarp_mbuf, struct ether_hdr *);
> > +	memset(eth_hdr->d_addr.addr_bytes, 0xff, ETHER_ADDR_LEN);
> > +	ether_addr_copy(mac, &eth_hdr->s_addr);
> > +	eth_hdr->ether_type = htons(ETHER_TYPE_RARP);
> > +
> > +	/* RARP header. */
> > +	rarp = (struct arp_hdr *)(eth_hdr + 1);
> > +	rarp->arp_hrd = htons(ARP_HRD_ETHER);
> > +	rarp->arp_pro = htons(ETHER_TYPE_IPv4);
> > +	rarp->arp_hln = ETHER_ADDR_LEN;
> > +	rarp->arp_pln = 4;
> > +	rarp->arp_op  = htons(ARP_OP_REVREQUEST);
> > +
> > +	ether_addr_copy(mac, &rarp->arp_data.arp_sha);
> > +	ether_addr_copy(mac, &rarp->arp_data.arp_tha);
> > +	memset(&rarp->arp_data.arp_sip, 0x00, 4);
> > +	memset(&rarp->arp_data.arp_tip, 0x00, 4);
> > +
> > +	rarp_mbuf->data_len = RARP_PKT_SIZE;
> > +	rarp_mbuf->pkt_len = RARP_PKT_SIZE;
> > +
> > +	return 0;
> > +}
> 
> Do you think it could make sense to have this function in a lib, as
> vhost user lib does exactly the same?
> 
> I don't know if it could be useful to others than vhost/virtio though.

Hi Thomas,

Do you think it's worth adding a new helper for ARP in lib/librte_net/?
Currently we just need a helper to build RARP packet (the above make_rarp_packet)

BRs,
Xiao


> 
> Thanks,
> Maxime