KVM: allow netboot

With this patch we allow KVM instances to be booted off the network.
The only issue is that this is not compatible with virtio nics, so
we disallow them, when booting from the net.

Reviewed-by: iustinp

lib/hypervisor/hv_kvm.py

@@ -236,6 +236,10 @@ class KVMHypervisor(hv_base.BaseHypervisor):
 
     boot_disk = (instance.hvparams[constants.HV_BOOT_ORDER] == "disk")
     boot_cdrom = (instance.hvparams[constants.HV_BOOT_ORDER] == "cdrom")
+    boot_network = (instance.hvparams[constants.HV_BOOT_ORDER] == "network")
+
+    if boot_network:
+      kvm_cmd.extend(['-boot', 'n'])
 
     disk_type = instance.hvparams[constants.HV_DISK_TYPE]
     if disk_type == constants.HT_DISK_PARAVIRTUAL:
@@ -250,6 +254,7 @@ class KVMHypervisor(hv_base.BaseHypervisor):
       if boot_disk:
         kvm_cmd.extend(['-boot', 'c'])
         boot_val = ',boot=on'
+        # We only boot from the first disk
         boot_disk = False
       else:
         boot_val = ''
@@ -755,8 +760,9 @@ class KVMHypervisor(hv_base.BaseHypervisor):
                                    " an absolute path, if defined")
 
     boot_order = hvparams[constants.HV_BOOT_ORDER]
-    if boot_order not in ('cdrom', 'disk'):
-      raise errors.HypervisorError("The boot order must be 'cdrom' or 'disk'")
+    if boot_order not in ('cdrom', 'disk', 'network'):
+      raise errors.HypervisorError("The boot order must be 'cdrom', 'disk' or"
+                                   " 'network'")
 
     if boot_order == 'cdrom' and not iso_path:
       raise errors.HypervisorError("Cannot boot from cdrom without an ISO path")
@@ -767,6 +773,9 @@ class KVMHypervisor(hv_base.BaseHypervisor):
                                    " hypervisor. Please choose one of: %s" %
                                    (nic_type,
                                     constants.HT_KVM_VALID_NIC_TYPES))
+    elif boot_order == 'network' and nic_type == constants.HT_NIC_PARAVIRTUAL:
+      raise errors.HypervisorError("Cannot boot from a paravirtual NIC. Please"
+                                   " change the nic type.")
 
     disk_type = hvparams[constants.HV_DISK_TYPE]
     if disk_type not in constants.HT_KVM_VALID_DISK_TYPES: