[Libguestfs] [v2v PATCH v2] RHV outputs: limit copied disk count to 23

[Richard W.M. Jones]

On Fri, Jun 17, 2022 at 11:53:37AM +0200, Laszlo Ersek wrote:
> We currently support virtio-blk (commonly) or IDE (unusually) for exposing
> disks to the converted guest; refer to "guestcaps.gcaps_block_bus" in
> "lib/create_ovf.ml". When using virtio-blk (i.e., in the common case), RHV
> can deal with at most 23 disks, as it plugs each virtio-blk device in a
> separate slot on the PCI(e) root bus; and the other slots are reserved for
> various purposes. When a domain has too many disks, the problem only
> becomes apparent once the copying finishes and an import is attempted.
> Modify the RHV outputs to fail relatively early when a domain has more
> than 23 disks that need to be copied.
> 
> Notes:
> 
> - With IDE, the theoretical limit may even be as low as 4. However, in the
>   "Output_module.setup" function, we don't have access to
>   "guestcaps.gcaps_block_bus", and in practice the IDE limitation has not
>   caused surprises. So for now stick with 23, assuming virtio-blk.
>   Modifying the "Output_module.setup" parameter list just for this seems
>   overkill.
> 
> - We could move the new check to an even earlier step, namely
>   "Output_module.parse_options", due to the v2v directory deliberately
>   existing (and having been populated with input sockets) at that time.
>   However, even discounting the fact that "parse_options" is not a good
>   name for including this kind of step, "parse_options" does not have
>   access to the v2v directory name, and modifying the signature just for
>   this is (again) overkill.
> 
> - By adding the check to "Output_module.setup", we waste *some* effort
>   (namely, the conversion occurs between "parse_options" and "setup"),
>   but: (a) the "rhv-disk-uuid" count check (against the disk count) is
>   already being done in the rhv-upload module's "setup" function, (b) in
>   practice the slowest step ought to be the copying, and placing the new
>   check in "setup" is early enough to prevent that.
> 
> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2051564
> Signed-off-by: Laszlo Ersek <lersek at redhat.com>
> ---
> 
> Notes:
>     v2:
>     
>     - rename "bail_if_disk_count_gt" to "error_if_disk_count_gt" [Rich]
>     
>     v1:
>     
>     This patch can be tested easily by replacing 23 with 0 in all three
>     affected output modules -- then the following test cases all fail in
>     "make check":
>     
>     FAIL: test-v2v-o-rhv.sh
>     FAIL: test-v2v-o-vdsm-options.sh
>     FAIL: test-v2v-o-rhv-upload.sh
>     
>     > [  11.3] Setting up the destination: -o rhv
>     > virt-v2v: error: this output module doesn't support copying more than 0 disks
>     
>     > [   9.0] Setting up the destination: -o vdsm
>     > virt-v2v: error: this output module doesn't support copying more than 0 disks
>     
>     > [  11.2] Setting up the destination: -o rhv-upload -oc https://example.com/ovirt-engine/api -os Storage
>     > virt-v2v: error: this output module doesn't support copying more than 0 disks
> 
>  output/output.mli           | 7 +++++++
>  output/output.ml            | 5 +++++
>  output/output_rhv.ml        | 1 +
>  output/output_rhv_upload.ml | 1 +
>  output/output_vdsm.ml       | 1 +
>  5 files changed, 15 insertions(+)
> 
> diff --git a/output/output.mli b/output/output.mli
> index 533a0c51d31c..8d3d6865945f 100644
> --- a/output/output.mli
> +++ b/output/output.mli
> @@ -76,6 +76,13 @@ val get_disks : string -> (int * int64) list
>  (** Examines the v2v directory and opens each input socket (in0 etc),
>      returning a list of input disk index and size. *)
>  
> +val error_if_disk_count_gt : string -> int -> unit
> +(** This function lets an output module enforce a maximum disk count.
> +    [error_if_disk_count_gt dir n] checks whether the domain has more than [n]
> +    disks that need to be copied, by examining the existence of input NBD socket
> +    "in[n]" in the v2v directory [dir].  If the socket exists, [error] is
> +    called. *)
> +
>  val output_to_local_file : ?changeuid:((unit -> unit) -> unit) ->
>                             Types.output_allocation ->
>                             string -> string -> int64 -> string ->
> diff --git a/output/output.ml b/output/output.ml
> index 10e685c46926..5c6670b99c69 100644
> --- a/output/output.ml
> +++ b/output/output.ml
> @@ -64,6 +64,11 @@ let get_disks dir =
>    in
>    loop [] 0
>  
> +let error_if_disk_count_gt dir n =
> +  let socket = sprintf "%s/in%d" dir n in
> +  if Sys.file_exists socket then
> +    error (f_"this output module doesn't support copying more than %d disks") n
> +
>  let output_to_local_file ?(changeuid = fun f -> f ())
>        output_alloc output_format filename size socket =
>    (* Check nbdkit is installed and has the required plugin. *)
> diff --git a/output/output_rhv.ml b/output/output_rhv.ml
> index 119207fdc065..8571e07b0cc3 100644
> --- a/output/output_rhv.ml
> +++ b/output/output_rhv.ml
> @@ -56,6 +56,7 @@ module RHV = struct
>      (options.output_alloc, options.output_format, output_name, output_storage)
>  
>    let rec setup dir options source =
> +    error_if_disk_count_gt dir 23;
>      let disks = get_disks dir in
>      let output_alloc, output_format, output_name, output_storage = options in
>  
> diff --git a/output/output_rhv_upload.ml b/output/output_rhv_upload.ml
> index 828996b36261..f2ced4f4e98e 100644
> --- a/output/output_rhv_upload.ml
> +++ b/output/output_rhv_upload.ml
> @@ -133,6 +133,7 @@ after their uploads (if you do, you must supply one for each disk):
>      else PCRE.matches (Lazy.force rex_uuid) uuid
>  
>    let rec setup dir options source =
> +    error_if_disk_count_gt dir 23;
>      let disks = get_disks dir in
>      let output_conn, output_format,
>          output_password, output_name, output_storage,
> diff --git a/output/output_vdsm.ml b/output/output_vdsm.ml
> index a1e8c2465810..23d1b9cd25b4 100644
> --- a/output/output_vdsm.ml
> +++ b/output/output_vdsm.ml
> @@ -119,6 +119,7 @@ For each disk you must supply one of each of these options:
>       compat, ovf_flavour)
>  
>    let setup dir options source =
> +    error_if_disk_count_gt dir 23;
>      let disks = get_disks dir in
>      let output_alloc, output_format,
>          output_name, output_storage,

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

Thanks,

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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