[Libguestfs] [PATCH] rhv-upload: Support qcow2 disks

[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 specify qcow2 disk format.

I think we need a way to expose the capabilities of the output to the
user. For example, can we use qcow2 format.

Issues:

- I hacked qemu-img convert command line to always use -O raw instead of
  "-O t.target_format" since oVirt always starts qemu-nbd with the actual
  disk format. This works for this plugin, but may be wrong for other
  plugins.
---
 v2v/output_rhv_upload.ml |  5 ++---
 v2v/rhv-upload-plugin.py | 19 +++++++++++++++++++
 v2v/v2v.ml               |  4 +++-
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/v2v/output_rhv_upload.ml b/v2v/output_rhv_upload.ml
index 3514714b..481eb482 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
    *)
@@ -333,8 +333,7 @@ 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 a2d09458..4272a89f 100644
--- a/v2v/rhv-upload-plugin.py
+++ b/v2v/rhv-upload-plugin.py
@@ -17,6 +17,7 @@
 # 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 
 import builtins
+import inspect
 import json
 import logging
 import socket
@@ -456,6 +457,8 @@ 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'].
@@ -497,11 +500,16 @@ 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,
         )
     )
 
@@ -531,6 +539,17 @@ def create_transfer(connection, disk, host):
 
     return transfer
 
+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):
diff --git a/v2v/v2v.ml b/v2v/v2v.ml
index 03590c9e..58bb06c3 100644
--- a/v2v/v2v.ml
+++ b/v2v/v2v.ml
@@ -739,7 +739,9 @@ and copy_targets cmdline targets input output =
           | TargetURI uri -> uri in
         [ "qemu-img"; "convert" ] @
         (if not (quiet ()) then [ "-p" ] else []) @
-        [ "-n"; "-f"; "qcow2"; "-O"; t.target_format ] @
+        (* XXX When using NBD we must use raw format, not the target_format
+        * which is the disk format. commpressed format will also not work. *)
+        [ "-n"; "-f"; "qcow2"; "-O"; "raw" ] @
         (if cmdline.compressed then [ "-c" ] else []) @
         [ "-S"; "64k" ] @
         [ overlay_file; filename ] in
-- 
2.21.0