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

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