DNS: Add basic support for asynchronous DNS resolving

This patch is a simple implementation for the proposal discussed in
https://mail.openvswitch.org/pipermail/ovs-dev/2017-August/337038.html and
https://mail.openvswitch.org/pipermail/ovs-dev/2017-October/340013.html.

It enables ovs-vswitchd and other utilities to use DNS names when specifying
OpenFlow and OVSDB remotes.

Below are some of the features and limitations of this patch:
    - Resolving is asynchornous in daemon context, avoiding blocking main loop;
    - Resolving is synchronous in general utility context;
    - Both IPv4 and IPv6 are supported;
    - The resolving API is thread-safe;
    - Depends on the unbound library;
    - When multiple ip addresses are returned, only the first one is used;
    - /etc/nsswitch.conf isn't respected as unbound library doesn't look at it;
    - For async-resolving, caller need to retry later; there is no callback.

Signed-off-by: Yifeng Sun <pkusunyifeng@gmail.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>

1 files changed, 3 insertions, 1 deletions

diff --git a/debian/control b/debian/control
index a4c031d85..9ae248f27 100644
--- a/debian/control
+++ b/debian/control
@@ -16,7 +16,8 @@ Build-Depends: graphviz,
                python-all (>= 2.7),
                python-twisted-conch,
                python-zopeinterface,
-               python-six
+               python-six,
+               libunbound-dev
 Standards-Version: 3.9.3
 Homepage: http://openvswitch.org/
 
@@ -307,6 +308,7 @@ Multi-Arch: same
 Depends:
  libopenvswitch (>= ${binary:Version}),
  libssl-dev,
+ libunbound-dev,
  ${misc:Depends}
 Conflicts: openvswitch-dev
 Replaces: openvswitch-dev