[Libguestfs] [PATCH v2 3/3] rhv-upload: Support qcow2 disk format

[Nir Soffer]

When using oVirt >= 4.3, we can enable the NBD based backend in imageio
by specifying that we transfer raw data when creating a transfer. With  
the NBD backend, we can import to disks using qcow2 format.

To make it work, we override output#transfer_format to return always raw
format, but we create the disk on RHV side using qcow2 format.

The pipeline looks like this:

    qemu-img convert <nbd> rhv-upload <http> imageio <nbd> qemu-nbd
---
 v2v/output_rhv_upload.ml |  7 ++++---
 v2v/rhv-upload-plugin.py | 19 +++++++++++++++++++
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/v2v/output_rhv_upload.ml b/v2v/output_rhv_upload.ml
index 3514714b..7b5ad7a8 100644
--- a/v2v/output_rhv_upload.ml
+++ b/v2v/output_rhv_upload.ml
@@ -174,7 +174,7 @@ See also the virt-v2v-output-rhv(1) manual.")
       error (f_"nbdkit was compiled without SELinux support.  You will have to recompile nbdkit with libselinux-devel installed, or else set SELinux to Permissive mode while doing the conversion.")
   in
 
-  (* Output format/sparse must be raw/sparse.  We may be able to
+  (* Output sparse must be sparse.  We may be able to
    * lift this limitation in future, but it requires changes on the
    * RHV side.  See TODO file for details.  XXX
    *)
@@ -287,6 +287,8 @@ object
 
   method supported_firmware = [ TargetBIOS; TargetUEFI ]
 
+  method transfer_format t = "raw"
+
   (* rhev-apt.exe will be installed (if available). *)
   method install_rhev_apt = true
 
@@ -333,8 +335,7 @@ object
         let disk_format =
           match target_format with
           | "raw" as fmt -> fmt
-          | "qcow2" ->
-             error_current_limitation "-of raw"
+          | "qcow2" as fmt -> fmt
           | _ ->
              error (f_"rhv-upload: -of %s: Only output format ‘raw’ or ‘qcow2’ is supported.  If the input is in a different format then force one of these output formats by adding either ‘-of raw’ or ‘-of qcow2’ on the command line.")
                    target_format in
diff --git a/v2v/rhv-upload-plugin.py b/v2v/rhv-upload-plugin.py
index a9e82250..75e4f404 100644
--- a/v2v/rhv-upload-plugin.py
+++ b/v2v/rhv-upload-plugin.py
@@ -18,6 +18,7 @@
 
 import builtins
 import functools
+import inspect
 import json
 import logging
 import socket
@@ -448,6 +449,8 @@ def create_disk(connection):
             name = params['disk_name'],
             description = "Uploaded by virt-v2v",
             format = disk_format,
+            # XXX For qcow2 disk on block storage, we should use the estimated
+            # size, based on qemu-img measure of the overlay.
             initial_size = params['disk_size'],
             provisioned_size = params['disk_size'],
             # XXX Ignores params['output_sparse'].
@@ -489,11 +492,16 @@ def create_transfer(connection, disk, host):
     system_service = connection.system_service()
     transfers_service = system_service.image_transfers_service()
 
+    extra = {}
+    if transfer_supports_format():
+        extra["format"] = types.DiskFormat.RAW
+
     transfer = transfers_service.add(
         types.ImageTransfer(
             disk = types.Disk(id = disk.id),
             host = host,
             inactivity_timeout = 3600,
+            **extra,
         )
     )
 
@@ -591,6 +599,17 @@ def finalize_transfer(connection, transfer, disk_id):
                 "timed out waiting for transfer %s to finalize"
                 % transfer.id)
 
+def transfer_supports_format():
+    """
+    Return True if transfer supports the "format" argument, enabing the NBD
+    bakend on imageio side, which allows uploading to qcow2 images.
+
+    This feature was added in ovirt 4.3. We assume that the SDK version matches
+    engine version.
+    """
+    sig = inspect.signature(types.ImageTransfer)
+    return "format" in sig.parameters
+
 # oVirt imageio operations
 
 def parse_transfer_url(transfer):
-- 
2.21.0