[libvirt] [PATCH 2/2] migration: allow migration to succeed when given destination ip

[Justin Clift]

This fixes a problem where migration fails when a destination
host uses a wrongly configured hostname, that doesn't resolve
correctly.

If we're given the direct IP address of the destination host,
the migration will now use this instead of the resolved host
name, allowing things to work.

Addresses BZ # 615941:

    https://bugzilla.redhat.com/show_bug.cgi?id=615941
---

Please note.  The DEBUG() and DEBUG0() statements in the code below don't
seem to output anywhere.  Left them in for now, in the assumption the problem
is somewhere in my system configuration.

Happy to remove them entirely if that's a better idea.

 src/libvirt.c |   66 +++++++++++++++++++++++++++++++++++++++++++++++++++++++-
 1 files changed, 64 insertions(+), 2 deletions(-)

diff --git a/src/libvirt.c b/src/libvirt.c
index 3ec5724..05e8d76 100644
--- a/src/libvirt.c
+++ b/src/libvirt.c
@@ -39,6 +39,7 @@
 #include "uuid.h"
 #include "util.h"
 #include "memory.h"
+#include "network.h"
 
 #ifndef WITH_DRIVER_MODULES
 # ifdef WITH_TEST
@@ -3280,6 +3281,7 @@ virDomainMigrateVersion2 (virDomainPtr domain,
                           unsigned long bandwidth)
 {
     virDomainPtr ddomain = NULL;
+    char *new_uri = NULL;
     char *uri_out = NULL;
     char *cookie = NULL;
     char *dom_xml = NULL;
@@ -3332,8 +3334,68 @@ virDomainMigrateVersion2 (virDomainPtr domain,
         virDispatchError(domain->conn);
         goto done;
     }
-    if (uri_out)
-        uri = uri_out; /* Did domainMigratePrepare2 change URI? */
+
+    if (uri_out) {
+        /* We need to determine the best server address to use for the
+         * destination host.  We potentially have a choice of (up to) two:
+         *
+         *   a) The server address given to the migration function on the
+         *      source, whose info must be ok otherwise we wouldn't have
+         *      made it this far through the code, or
+         *
+         *   b) The server address returned to us by the destination
+         *      host itself (may be broken in some situations)
+         *
+         * We decide by checking if the address given for a) above is a
+         * numeric IP address.  If it is, we know that's good, so we
+         * prefer that over anything given to us by the destination host.
+         */
+
+        DEBUG("URI returned by the destination host: '%s'", uri_out);
+
+        /* Check if the server adress we were originally given is an IP */
+        if (virIsNumericIPAddr(dconn->uri->server) != 0) {
+            /* The server address we were passed from the source isn't
+             * a numeric IP address.  It's likely a host name in text form.
+             * Therefore, we instead use the URI provided to us by the
+             * destination server.
+             */
+            DEBUG0("Server address in URI is not numeric-only");
+            uri = uri_out;
+        } else {
+            /* The server address we were passed from the source *is* a
+             * numeric IP address.  We recreate the URI given to us by the
+             * destination server, but using this "known good" IP address
+             * instead.
+             */
+
+            DEBUG0("Server address in URI is numeric-only");
+
+            char *transport;
+            char *destGivenHostname;
+            char *destGivenPort;
+            transport = strtok(uri_out, ":");
+            destGivenHostname = strtok(NULL, ":");
+            destGivenPort = strtok(NULL, ":");
+            DEBUG("URI extracted strings; transport: '%s', "
+                  "destination address: '%s', destination port: '%s'",
+                  transport, destGivenHostname, destGivenPort);
+            ret = virAsprintf(&new_uri, "%s:%s:%s",
+                              transport,
+                              dconn->uri->server,
+                              destGivenPort);
+            if (ret < 0) {
+                /* An error occurred when creating the new URI string, so fall
+                 * back to using the URI provided by the destination server.
+                 */
+                uri = uri_out;
+            } else {
+                /* String creation worked, so use it */
+                uri = new_uri;
+            }
+            DEBUG("URI we'll be using: '%s'", uri);
+        }
+    }
     assert (uri != NULL);
 
     /* Perform the migration.  The driver isn't supposed to return
-- 
1.7.2.1