[Libguestfs] [PATCH 2/5] v2v/lib/util.ml: Get disk allocation from input

[Richard W.M. Jones]

On Sat, Dec 18, 2021 at 10:36:30PM +0200, Nir Soffer wrote:
> After finalizing the transfer, virt-v2v try to connect to the output
> socket and query disk allocation. This may work for some outputs
> supporting block status, but for rhv_upload output this cannot work for
> 2 reasons:
> - The rhv-upload-plugin does not support extents
> - The transfer was finalized before this call, so the plugin lost access
>   to the image.
> 
> Here is an example failure log:
> 
> [  74.2] Creating output metadata
> python3 '/tmp/v2v.WMq8Tk/rhv-upload-finalize.py' '/tmp/v2v.WMq8Tk/params6.json'
> finalizing transfer b03fe3ba-a4ff-4634-a0a0-10b3daba3cc2
> ...
> transfer b03fe3ba-a4ff-4634-a0a0-10b3daba3cc2 finalized in 2.118 seconds
> ...
> nbdkit: debug: accepted connection
> ...
> nbdkit: python[4]: debug: python: close
> virt-v2v: error: exception: NBD.Error("nbd_block_status: request out of
> bounds: Invalid argument", 22)
> 
> Fix by using the input socket.
> ---
>  lib/utils.ml | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/lib/utils.ml b/lib/utils.ml
> index d6861d08..f6c85543 100644
> --- a/lib/utils.ml
> +++ b/lib/utils.ml
> @@ -171,21 +171,21 @@ let with_nbd_connect_unix ~socket ~meta_contexts ~f =
>      ~f:(fun () ->
>            List.iter (NBD.add_meta_context nbd) meta_contexts;
>            NBD.connect_unix nbd socket;
>            protect
>              ~f:(fun () -> f nbd)
>              ~finally:(fun () -> NBD.shutdown nbd)
>         )
>      ~finally:(fun () -> NBD.close nbd)
>  
>  let get_disk_allocated ~dir ~disknr =
> -  let socket = sprintf "%s/out%d" dir disknr
> +  let socket = sprintf "%s/in%d" dir disknr

This patch is definitely wrong - we need to get the allocation size
from the output disk.  Options such as -oa preallocated, and just
general issues like block size, nbdcopy sparseness detection etc,
would affect this.

It probably indicates a problem with rhv-upload-plugin (again) that
it's not really prepared to be an idempotent part of a disk image
pipeline.

Rich.

>    and alloc_ctx = "base:allocation" in
>    with_nbd_connect_unix ~socket ~meta_contexts:[alloc_ctx]
>      ~f:(fun nbd ->
>           if NBD.can_meta_context nbd alloc_ctx then (
>             (* Get the list of extents, using a 2GiB chunk size as hint. *)
>             let size = NBD.get_size nbd
>             and allocated = ref 0_L
>             and fetch_offset = ref 0_L in
>             while !fetch_offset < size do
>               let remaining = size -^ !fetch_offset in
> -- 
> 2.33.1

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