Libguestfs - Mar 2022 - [PATCH p2v] ssh: Allow interop with virt-v2v 2.0

On 03/23/22 18:04, Richard W.M. Jones wrote:
> The code previously checked that the remote version of virt-v2v was
> 1.x and >= 1.28.  Since virt-v2v 2.0 has been released and is broadly
> compatible, allow 2.0 as well.
> ---
>  ssh.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/ssh.c b/ssh.c
> index ce0caaa..7ac43eb 100644
> --- a/ssh.c
> +++ b/ssh.c
> @@ -1030,11 +1030,11 @@ add_output_driver (const char *name, size_t len)
>  static int
>  compatible_version (const char *v2v_version)
>  {
> -  unsigned v2v_minor;
> +  unsigned v2v_major, v2v_minor;
>  
> -  /* The major version must always be 1. */
> -  if (!STRPREFIX (v2v_version, "1.")) {
> -    set_ssh_error ("virt-v2v major version is not 1
(\"%s\"), "
> +  /* The major version must always be 1 or 2. */
> +  if (! (STRPREFIX (v2v_version, "1.") || STRPREFIX
(v2v_version, "2."))) {
> +    set_ssh_error ("virt-v2v major version is not 1 or 2
(\"%s\"), "
>                     "this version of virt-p2v is not
compatible.",
>                     v2v_version);
>      return 0;
I have a personal preference for avoiding such "outermost" logical
negations; I always move negations as far inside as possible, using De
Morgan's Laws:

  !STRPREFIX (v2v_version, "1.") && !STRPREFIX (v2v_version,
"2.")

However, this is just a style question, and the logic is certainly correct.

Somewhat relatedly, regarding the English language error message, I
think we could slightly clarify it:

  virt-v2v major version is neither 1 nor 2

The rest looks OK to me.

With or without the msg update:

Reviewed-by: Laszlo Ersek <lersek at redhat.com>

Thanks
Laszlo
> @@ -1045,13 +1045,13 @@ compatible_version (const char *v2v_version)
>     * that we published during development, nor (b) using old virt-v2v.
>     * We should remain compatible with any virt-v2v after 1.28.
>     */
> -  if (sscanf (v2v_version, "1.%u", &v2v_minor) != 1) {
> +  if (sscanf (v2v_version, "%u.%u", &v2v_major,
&v2v_minor) != 2) {
>      set_ssh_internal_error ("cannot parse virt-v2v version string
(\"%s\")",
>                              v2v_version);
>      return 0;
>    }
>  
> -  if (v2v_minor < 28) {
> +  if (v2v_major == 1 && v2v_minor < 28) {
>      set_ssh_error ("virt-v2v version is < 1.28 (\"%s\"),
"
>                     "you must upgrade to virt-v2v >= 1.28 on "
>                     "the conversion server.", v2v_version);
>

Thanks - pushed that as commit 546f3a6.

While I remember, there's another odd thing about virt-p2v that could
be simplified if you're looking for some general clean-up work to do
to get used to the code.

virt-p2v needs an NBD server running on the p2v machine to export the
disks.  Originally we used qemu-nbd since that was the only choice.
In 2017, I added support for nbdkit as an alternative to qemu-nbd.

So now we're in the situation where either server can be used (see
virt-p2v.git/nbd.c).  For added complexity we also support both
servers in either systemd socket activation (SA) mode or "no-SA" mode,
so that's 4 combinations.

This is silly, we should support only one NBD server, and since
systemd socket activation is well-supported and more flexible, we
should just use it.

So the question is *which* NBD server to support.  That's not so much
a technical matter since both servers can easily serve a local block
device (always raw format).  However I do think that nbdkit might
genuinely be the better choice here:

 - qemu-nbd links to the whole qemu block layer, nbdkit can be shipped
   with just the plugin we need, so it should be smaller with less
   code surface

 - nbdkit-file-plugin has a better method of not trashing the host
   page cache

 - could use nbdkit --exit-with-parent feature (which we don't at the
   moment)

 - nbdkit is widely available in distros these days

Also that file uses AI_ADDRCONFIG so I guess it has problems with IPv6.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
nbdkit - Flexible, fast NBD server with plugins
https://gitlab.com/nbdkit/nbdkit