Re: [PATCH net-next 2/5] vxlan: support fdb and learning in COLLECT_METADATA mode

From: Roopa Prabhu <redacted>

Vxlan COLLECT_METADATA mode today solves the per-vni netdev
scalability problem in l3 networks. It expects all forwarding
information to be present in dst_metadata. This patch series
enhances collect metadata mode to include the case where only
vni is present in dst_metadata, and the vxlan driver can then use
the rest of the forwarding information datbase to make forwarding
decisions. There is no change to default COLLECT_METADATA
behaviour. These changes only apply to COLLECT_METADATA when
used with the bridging use-case with a special dst_metadata
tunnel info flag (eg: where vxlan device is part of a bridge).
For all this to work, the vxlan driver will need to now support a
single fdb table hashed by mac + vni. This series essentially makes
this happen.

use-case and workflow:
vxlan collect metadata device participates in bridging vlan
to vn-segments. Bridge driver above the vxlan device,
sends the vni corresponding to the vlan in the dst_metadata.
vxlan driver will lookup forwarding database with (mac + vni)
for the required remote destination information to forward the
packet.

Changes introduced by this patch:
    - allow learning and forwarding database state in vxlan netdev in
      COLLECT_METADATA mode. Current behaviour is not changed
      by default. tunnel info flag IP_TUNNEL_INFO_BRIDGE is used
      to support the new bridge friendly mode.
    - A single fdb table hashed by (mac, vni) to allow fdb entries with
      multiple vnis in the same fdb table
    - rx path already has the vni
    - tx path expects a vni in the packet with dst_metadata
    - prior to this series, fdb remote_dsts carried remote vni and
      the vxlan device carrying the fdb table represented the
      source vni. With the vxlan device now representing multiple vnis,
      this patch adds a src vni attribute to the fdb entry. The remote
      vni already uses NDA_VNI attribute. This patch introduces
      NDA_SRC_VNI netlink attribute to represent the src vni in a multi
      vni fdb table.

iproute2 example (patched and pruned iproute2 output to just show
relevant fdb entries):
example shows same host mac learnt on two vni's.

before (netdev per vni):
$bridge fdb show | grep "00:02:00:00:00:03"
00:02:00:00:00:03 dev vxlan1001 dst 12.0.0.8 self
00:02:00:00:00:03 dev vxlan1000 dst 12.0.0.8 self

after this patch with collect metadata in bridged mode (single netdev):
$bridge fdb show | grep "00:02:00:00:00:03"
00:02:00:00:00:03 dev vxlan0 src_vni 1001 dst 12.0.0.8 self
00:02:00:00:00:03 dev vxlan0 src_vni 1000 dst 12.0.0.8 self

Signed-off-by: Roopa Prabhu <redacted>
---
 drivers/net/vxlan.c            |  211 +++++++++++++++++++++++++---------------
 include/uapi/linux/neighbour.h |    1 +
 2 files changed, 136 insertions(+), 76 deletions(-)

diff --git a/drivers/net/vxlan.c b/drivers/net/vxlan.c
index 19b1653..b80c405 100644
--- a/drivers/net/vxlan.c
+++ b/drivers/net/vxlan.c

@@ -57,6 +57,8 @@
 
 static const u8 all_zeros_mac[ETH_ALEN + 2];
 
+static u32 fdb_salt __read_mostly;
+
 static int vxlan_sock_add(struct vxlan_dev *vxlan);
 
 /* per-network namespace private data for this module */

@@ -75,6 +77,7 @@ struct vxlan_fdb {
 	struct list_head  remotes;
 	u8		  eth_addr[ETH_ALEN];
 	u16		  state;	/* see ndm_state */
+	__be32		  vni;
 	u8		  flags;	/* see ndm_flags */
 };
 

@@ -302,6 +305,10 @@ static int vxlan_fdb_info(struct sk_buff *skb, struct vxlan_dev *vxlan,
 	if (rdst->remote_vni != vxlan->default_dst.remote_vni &&
 	    nla_put_u32(skb, NDA_VNI, be32_to_cpu(rdst->remote_vni)))
 		goto nla_put_failure;
+	if ((vxlan->flags & VXLAN_F_COLLECT_METADATA) && fdb->vni &&
+	    nla_put_u32(skb, NDA_SRC_VNI,
+			be32_to_cpu(fdb->vni)))
+		goto nla_put_failure;
 	if (rdst->remote_ifindex &&
 	    nla_put_u32(skb, NDA_IFINDEX, rdst->remote_ifindex))
 		goto nla_put_failure;

@@ -400,34 +407,51 @@ static u32 eth_hash(const unsigned char *addr)
 	return hash_64(value, FDB_HASH_BITS);
 }
 
+static u32 eth_vni_hash(const unsigned char *addr, __be32 vni)
+{
+	/* use 1 byte of OUI and 3 bytes of NIC */
+	u32 key = get_unaligned((u32 *)(addr + 2));
+
+	return jhash_2words(key, vni, fdb_salt) & (FDB_HASH_SIZE - 1);