virt-v2v/0002-input-xen-Fix-assertion-error-when-importing-from-re.patch

From f3180e3c0ef59ab52983903ff806014a4a3171a5 Mon Sep 17 00:00:00 2001
From: "Richard W.M. Jones" <rjones@redhat.com>
Date: Tue, 18 Jan 2022 12:37:51 +0000
Subject: [PATCH] input: xen: Fix assertion error when importing from remote
 block device

We never supported this because OpenSSH sftp server does not know how
to open and get the size of a block device.  Before modular virt-v2v,
we would detect this situation and print an error:

  virt-v2v: error: guest disk sda appears to be zero bytes in size.

  There could be several reasons for this:

  Check that the guest doesn't really have a zero-sized disk.  virt-v2v
  cannot convert such a guest.

  If you are converting a guest from an ssh source and the guest has a disk
  on a block device (eg. on a host partition or host LVM LV), then
  conversions of this type are not supported.  See the virt-v2v-input-xen(1)
  manual for a workaround.

This error was lost in the conversion to modularity, but in any case
the proper way to detect this is in the input_xen driver itself.

In addition to this, when we removed the old virt-v2v-copy-to-local
tool, the text referring to the workaround in the manual became
meaningless, so I added the (ugly, manual) workaround that you have to
do back into the manual, minus the bit about the tool that we removed.

In future we could consider other ways to convert a remote block
device over SSH transparently.  (Sending a "dd" command, maybe?)

I also checked what happens when we try to convert an empty disk, and
it fails during inspection with a reasonable error message, so we
don't need to do anything to restore the above error:

  $ virt-v2v -i disk /var/tmp/empty -o null
  [   1.1] Opening the source
  [   7.0] Inspecting the source
  virt-v2v: error: inspection could not detect the source guest (or physical
  machine).

  Assuming that you are running virt-v2v/virt-p2v on a source which is
  supported (and not, for example, a blank disk), then this should not
  happen.

  No root device found in this operating system image.

Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=2041852
Reported-by: Xiaodai Wang
---
 docs/virt-v2v-input-xen.pod |  5 +++++
 input/input_xen_ssh.ml      | 12 +++++++++++-
 2 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/docs/virt-v2v-input-xen.pod b/docs/virt-v2v-input-xen.pod
index 857a7095..c4948e5e 100644
--- a/docs/virt-v2v-input-xen.pod
+++ b/docs/virt-v2v-input-xen.pod
@@ -99,6 +99,11 @@ This happens because the qemu ssh block driver that we use to access
 remote disks uses the ssh sftp protocol, and this protocol cannot
 correctly detect the size of host block devices.
 
+The workaround is to copy the block device from the remote Xen
+server to a regular local file, copy the libvirt guest XML,
+adjust the C<disk> element to point to the local file, and use
+C<-i libvirtxml> mode instead.
+
 =head1 SEE ALSO
 
 L<virt-v2v(1)>.
diff --git a/input/input_xen_ssh.ml b/input/input_xen_ssh.ml
index 5bb46bde..cb8b1f91 100644
--- a/input/input_xen_ssh.ml
+++ b/input/input_xen_ssh.ml
@@ -87,9 +87,19 @@ let rec xen_ssh_source dir options args =
       On_exit.unlink socket;
 
       match d_type with
-      | BlockDev _ | NBD _ | HTTP _ -> (* These should never happen? *)
+      | NBD _ | HTTP _ -> (* These should never happen? *)
          assert false
 
+      | BlockDev _ ->
+         (* Conversion from a remote block device over SSH isn't
+          * supported because OpenSSH sftp server doesn't know how
+          * to get the size of a block device.  Therefore we disallow
+          * this and refer users to the manual.
+          *)
+         error (f_"input from xen over ssh does not support disks stored on \
+                   remote block devices.  See virt-v2v-input-xen(1) \
+                   section \"Xen or ssh conversions from block devices\".")
+
       | LocalFile path ->
          let cor = dir // "convert" in
          let bandwidth = options.bandwidth in
-- 
2.31.1