[Libguestfs] [PATCH v2 2/2] v2v: -o null: Use the qemu null device driver.

Instead of writing to a temporary file and deleting it, use the null block driver (the "null-co://" URI) in qemu to throw it away. --- v2v/output_null.ml | 43 +++++++++++++++++++++++++++++-------------- v2v/virt-v2v.pod | 4 ---- 2 files changed, 29 insertions(+), 18 deletions(-) diff --git a/v2v/output_null.ml b/v2v/output_null.ml index 65861a597..4a58d0621 100644 --- a/v2v/output_null.ml +++ b/v2v/output_null.ml @@ -26,16 +26,23 @@ open Common_gettext.Gettext open Types open Utils +(* Notes: + * + * This only happens to work because we run qemu-img convert + * with the -n [no create output] option, since null-co doesn't + * support creation. If -n is removed in the main program then + * the tests will break very obviously. + * + * The null-co device is not zero-sized. It actually has a fixed + * size (defaults to 2^30 I believe). + * + * qemu-img convert checks the output size and will fail if it's + * too small, so we have to set the size. We could set it to + * match the input size but it's easier to set it to some huge + * size instead. + *) + class output_null = - (* It would be nice to be able to write to /dev/null. - * Unfortunately qemu-img convert cannot do that. Instead create a - * temporary directory which is always deleted at exit. - *) - let tmpdir = - let base_dir = (open_guestfs ())#get_cachedir () in - let t = Mkdtemp.temp_dir ~base_dir "null." in - rmdir_on_exit t; - t in object inherit output @@ -44,11 +51,19 @@ object method supported_firmware = [ TargetBIOS; TargetUEFI ] method prepare_targets source targets = - List.map ( - fun t -> - let target_file = tmpdir // t.target_overlay.ov_sd in - { t with target_file = TargetFile target_file } - ) targets + let json_params = [ + "file.driver", JSON.String "null-co"; + "file.size", JSON.String "1E"; + ] in + let target_file = TargetURI ("json:" ^ JSON.string_of_doc json_params) in + + (* While it's not intended that output drivers can set the + * target_format field (thus overriding the -of option), in + * this special case of -o null it is reasonable. + *) + let target_format = "raw" in + + List.map (fun t -> { t with target_file; target_format }) targets method create_metadata _ _ _ _ _ _ = () end diff --git a/v2v/virt-v2v.pod b/v2v/virt-v2v.pod index 1cf58663b..503830c9d 100644 --- a/v2v/virt-v2v.pod +++ b/v2v/virt-v2v.pod @@ -1915,10 +1915,6 @@ This temporarily places a full copy of the output disks in C<$TMPDIR>. You must ensure there is sufficient space in the output directory for the converted guest. -=item I<-o null> - -This temporarily places a full copy of the output disks in C<$TMPDIR>. - =back See also L</Minimum free space check in the host> below. -- 2.13.2