[Libguestfs] [v2v PATCH v2] input_vmx: cleanly reject guests with snapshots when using "-it ssh"

[Richard W.M. Jones]

On Sat, Apr 09, 2022 at 08:12:52AM +0200, Laszlo Ersek wrote:
> For traversing a backing chain of VMDK descriptor files over ssh, two
> things are necessary:
> 
> - qemu-nbd with the ssh block driver, rather than nbdkit-ssh-plugin,
> 
> - a remote SSH URL (for qemu-nbd) without a query string appended, as
>   qemu-nbd cannot update the last pathname component (for tracking the
>   relative pathnames of VMDK descriptor files) if a query string is
>   appended.
> 
> Before commit 7a6f6113a25f ("v2v: -i vmx -it ssh: Replace qemu block ssh
> driver with nbdkit-ssh-plugin.", 2019-10-08), we passed the
> "?host_key_check=no" query string in the URL to qemu-nbd, so we can't just
> return to that, for accessing snapshotted guests with vmx+ssh.
> 
> But, we shouldn't return to qemu-nbd for vmx+ssh even without a query
> string, as that would undo the other benefit(s) of commit 7a6f6113a25f.
> 
> Instead, clearly document that snapshotted guests are not supported over
> vmx+ssh, and cleanly reject this situation in the code as well. Recommend
> the two alternative transports that allow the user to convert such guests.
> 
> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1774386
> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
> ---
> 
> Notes:
>     v2:
>     
>     - in the manual, centralize the description in a new NOTES section, and
>       reference that section from "-i vmx -it ssh" and "INPUT FROM VMWARE
>       VMX" [Rich]
>     
>     - in the code, bail out with error (f_"...") rather than failwith, for
>       enabling translations [Rich]

And line wrapping too ..

>     - in the error message printed from the code, recommend actions to the
>       user (reference the new NOTES section of the manual) [Rich]
> 
>  input/input_vmx.ml             | 27 ++++++++------------
>  docs/virt-v2v-input-vmware.pod | 18 ++++++++++++-
>  2 files changed, 27 insertions(+), 18 deletions(-)
> 
> diff --git a/input/input_vmx.ml b/input/input_vmx.ml
> index 9921419b5a85..eed8a4335622 100644
> --- a/input/input_vmx.ml
> +++ b/input/input_vmx.ml
> @@ -81,23 +81,16 @@ module VMX = struct
>  
>              let vmx_path = path_of_uri uri in
>              let abs_path = absolute_path_from_other_file vmx_path filename in
> -            let format = "vmdk" in
> +            let flat_vmdk = PCRE.replace (PCRE.compile "\\.vmdk$")
> +                              "-flat.vmdk" abs_path in
>  
> -            (* XXX This is a hack to work around qemu / VMDK limitation
> -             *   "Cannot use relative extent paths with VMDK descriptor file"
> -             * We can remove this if the above is fixed.
> -             *)
> -            let abs_path, format =
> -              let flat_vmdk =
> -                PCRE.replace (PCRE.compile "\\.vmdk$") "-flat.vmdk" abs_path in
> -              if remote_file_exists uri flat_vmdk then (flat_vmdk, "raw")
> -              else (abs_path, format) in
> -
> -            (* XXX In virt-v2v 1.42+ importing from VMX over SSH
> -             * was broken if the -flat.vmdk file did not exist.
> -             * It is still broken here.
> -             *)
> -            ignore format;
> +            (* RHBZ#1774386 *)
> +            if not (remote_file_exists uri flat_vmdk) then
> +              error (f_"This transport does not support guests with snapshots. \
> +                        Either collapse the snapshots for this guest and try \
> +                        the conversion again, or use one of the alternate \
> +                        conversion methods described in \
> +                        virt-v2v-input-vmware(1) section \"NOTES\".");
>  
>              let server = server_of_uri uri in
>              let port = Option.map string_of_int (port_of_uri uri) in
> @@ -110,7 +103,7 @@ module VMX = struct
>              let cor = dir // "convert" in
>              let bandwidth = options.bandwidth in
>              let nbdkit = Nbdkit_ssh.create_ssh ?bandwidth ~cor ~password
> -                           ~server ?port ?user abs_path in
> +                           ~server ?port ?user flat_vmdk in
>              let _, pid = Nbdkit.run_unix socket nbdkit in
>              On_exit.kill pid
>          ) filenames
> diff --git a/docs/virt-v2v-input-vmware.pod b/docs/virt-v2v-input-vmware.pod
> index 2c90e0afc7cd..66ca5f00d28a 100644
> --- a/docs/virt-v2v-input-vmware.pod
> +++ b/docs/virt-v2v-input-vmware.pod
> @@ -51,6 +51,9 @@ to ESXi to read the F<GUEST.vmx> file and associated disks.  This
>  requires that you have enabled SSH access to the VMware ESXi
>  hypervisor - in the default ESXi configuration this is turned off.
>  
> +This transport is incompatible with guests that have snapshots; refer
> +to L</NOTES>.
> +
>  =item B<-ic vpx://...> B<-it vddk>
>  
>  =item B<-ic esx://...> B<-it vddk>
> @@ -84,6 +87,18 @@ import a guest from VMware vCenter.  This is the slowest method.
>  
>  =back
>  
> +=head1 NOTES
> +
> +When accessing the F<I<guest>.vmx> file on ESXi over an SSH connection
> +(that is, when using the B<-i vmx> B<-it ssh> options), the conversion

The convention -- not written down anywhere :-( -- is to use
B<-option> when referencing the option first time in =item, and
I<-option> elsewhere.  See for example:

https://gitlab.com/nbdkit/nbdkit/-/commit/bc0d4f23ce08052db4c9cd3a1a563f5497270d84

So here it should be I<-i vmx> I<-it ssh> ...

> +will not work if the guest has snapshots (files called
> +F<I<guest>-000001.vmdk> and similar).  Either collapse the snapshots
> +for the guest and retry the conversion with the same
> +B<-i vmx> B<-it ssh> options, or leave the snapshots intact and use a
> +transport different from SSH: just B<-i vmx>, or
> +B<-ic vpx://...> B<-it vddk> or B<-ic esx://...> B<-it vddk>.  Refer

... and here too.

> +to L<https://bugzilla.redhat.com/1774386>.
> +
>  =head1 INPUT FROM VMWARE VMX
>  
>  Virt-v2v is able to import guests from VMware’s vmx files.
> @@ -106,7 +121,8 @@ a C</vmfs/volumes> folder containing the virtual machines.
>  
>  If you find a folder of files called F<I<guest>.vmx>,
>  F<I<guest>.vmxf>, F<I<guest>.nvram> and one or more F<.vmdk> disk
> -images, then you can use this method.
> +images, then you can use this method.  The SSH transport is not usable
> +if the guest has snapshots; refer to L</NOTES>.
>  
>  =head2 VMX: Guest must be shut down

With the B<> changed to I<> it's good to go, thanks, so:

Reviewed-by: Richard W.M. Jones <rjones at redhat.com>

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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