datapath: conntrack: Support conntrack zone limit

datapath: conntrack: Support conntrack zone limit

Upstream commit:
    commit 11efd5cb04a184eea4f57b68ea63dddd463158d1
    Author: Yi-Hung Wei <yihung.wei@gmail.com>
    Date:   Thu May 24 17:56:43 2018 -0700

    openvswitch: Support conntrack zone limit

    Currently, nf_conntrack_max is used to limit the maximum number of
    conntrack entries in the conntrack table for every network namespace.
    For the VMs and containers that reside in the same namespace,
    they share the same conntrack table, and the total # of conntrack entries
    for all the VMs and containers are limited by nf_conntrack_max.  In this
    case, if one of the VM/container abuses the usage the conntrack entries,
    it blocks the others from committing valid conntrack entries into the
    conntrack table.  Even if we can possibly put the VM in different network
    namespace, the current nf_conntrack_max configuration is kind of rigid
    that we cannot limit different VM/container to have different # conntrack
    entries.

    To address the aforementioned issue, this patch proposes to have a
    fine-grained mechanism that could further limit the # of conntrack entries
    per-zone.  For example, we can designate different zone to different VM,
    and set conntrack limit to each zone.  By providing this isolation, a
    mis-behaved VM only consumes the conntrack entries in its own zone, and
    it will not influence other well-behaved VMs.  Moreover, the users can
    set various conntrack limit to different zone based on their preference.

    The proposed implementation utilizes Netfilter's nf_conncount backend
    to count the number of connections in a particular zone.  If the number of
    connection is above a configured limitation, ovs will return ENOMEM to the
    userspace.  If userspace does not configure the zone limit, the limit
    defaults to zero that is no limitation, which is backward compatible to
    the behavior without this patch.

    The following high leve APIs are provided to the userspace:
      - OVS_CT_LIMIT_CMD_SET:
        * set default connection limit for all zones
        * set the connection limit for a particular zone
      - OVS_CT_LIMIT_CMD_DEL:
        * remove the connection limit for a particular zone
      - OVS_CT_LIMIT_CMD_GET:
        * get the default connection limit for all zones
        * get the connection limit for a particular zone

    Signed-off-by: Yi-Hung Wei <yihung.wei@gmail.com>
    Acked-by: Pravin B Shelar <pshelar@ovn.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Yi-Hung Wei <yihung.wei@gmail.com>
Signed-off-by: Justin Pettit <jpettit@ovn.org>