[Libguestfs] [PATCH] v2v: -o null: support older qemu-img (RHBZ#1580309)

[Richard W.M. Jones]

On Mon, May 21, 2018 at 05:28:18PM +0200, Pino Toscano wrote:
> Commit 4699c7b6e126e07c95b67fb95df58aed87a680dd converted the null
> output to use the null-co qemu driver with a JSON URL syntax --
> especially the latter is only available in newer versions of qemu.
> 
> Even if this output mode is mostly for testing, check at runtime whether
> the null-co + JSON way is possible, falling back to the creation of
> thrown-away temporary files as before.
> ---
>  v2v/output_null.ml | 60 +++++++++++++++++++++++++++++++++++++---------
>  1 file changed, 49 insertions(+), 11 deletions(-)
> 
> diff --git a/v2v/output_null.ml b/v2v/output_null.ml
> index b93d53dc5..5a5473c0d 100644
> --- a/v2v/output_null.ml
> +++ b/v2v/output_null.ml
> @@ -42,7 +42,37 @@ open Utils
>   * size instead.
>   *)
>  
> +let qemu_supports_null_co_device () =
> +  (* We actually attempt to convert a raw file to the null-co device. *)
> +  let tmp = Filename.temp_file "v2vqemunullcotst" ".img" in
> +  Unix.truncate tmp 1024;
> +
> +  let json = [
> +    "file.driver", JSON.String "null-co";
> +    "file.size", JSON.String "1E";
> +  ] in
> +
> +  let cmd =
> +    sprintf "qemu-img convert -n -f raw -O raw %s json:%s >/dev/null%s"
> +            (quote tmp)
> +            (quote (JSON.string_of_doc ~fmt:JSON.Compact json))
> +            (if verbose () then "" else " 2>&1") in
> +  debug "%s" cmd;
> +  let r = 0 = Sys.command cmd in
> +  Unix.unlink tmp;
> +  debug "qemu-img supports the null-co device: %b" r;
> +  r

I wonder if for consistency we should put this into v2v/utils.ml, and
also add a test to v2v/v2v_unit_tests.ml ...  (although the test for
Utils.qemu_img_supports_offset_and_size is kinda useless).

Rest of the patch looks good to me, so ACK.

Thanks,

Rich.

-- 
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