Implement capability to extend existing volume.

This patch adds the core components to implement extending
the size of an existing available volume.

Volume status must be available, and the format is:
    extend <vol-id> <new-size>

where new-size must be > current size.

Adding support to drivers will be handled in follow up
patches for each of the existing drivers.

Implements blueprint: volume-resize

Change-Id: I40026083e564ea2074757e11e13cd07cdae3e6cc

cinder/volume/api.py

@@ -780,6 +780,55 @@ class API(base.Base):
                     "image_name": recv_metadata.get('name', None)}
         return response
 
+    @wrap_check_policy
+    def extend(self, context, volume, new_size):
+        if volume['status'] != 'available':
+            msg = _('Volume status must be available to extend.')
+            raise exception.InvalidVolume(reason=msg)
+
+        size_increase = (int(new_size)) - volume['size']
+        if size_increase <= 0:
+            msg = (_("New size for extend must be greater "
+                     "than current size. (current: %(size)s, "
+                     "extended: %(new_size)s)") % {'new_size': new_size,
+                                                   'size': volume['size']})
+            raise exception.InvalidInput(reason=msg)
+        try:
+            reservations = QUOTAS.reserve(context, gigabytes=+size_increase)
+        except exception.OverQuota as exc:
+            overs = exc.kwargs['overs']
+            usages = exc.kwargs['usages']
+            quotas = exc.kwargs['quotas']
+
+            def _consumed(name):
+                return (usages[name]['reserved'] + usages[name]['in_use'])
+
+            if 'gigabytes' in overs:
+                msg = _("Quota exceeded for %(s_pid)s, "
+                        "tried to extend volume by "
+                        "%(s_size)sG, (%(d_consumed)dG of %(d_quota)dG "
+                        "already consumed)")
+                LOG.warn(msg % {'s_pid': context.project_id,
+                                's_size': size_increase,
+                                'd_consumed': _consumed('gigabytes'),
+                                'd_quota': quotas['gigabytes']})
+                raise exception.VolumeSizeExceedsAvailableQuota()
+
+        self.update(context, volume, {'status': 'extending'})
+
+        try:
+            self.volume_rpcapi.extend_volume(context, volume, new_size)
+        except Exception:
+            with excutils.save_and_reraise_exception():
+                try:
+                    self.update(context, volume, {'status': 'error_extending'})
+                finally:
+                    QUOTAS.rollback(context, reservations)
+
+        self.update(context, volume, {'size': new_size})
+        QUOTAS.commit(context, reservations)
+        self.update(context, volume, {'status': 'available'})
+
 
 class HostAPI(base.Base):
     def __init__(self):