[Libguestfs] [v2v PATCH] output_qemu: rewrite output disk mapping

[Laszlo Ersek]

On 04/17/22 11:04, Richard W.M. Jones wrote:
> On Sun, Apr 17, 2022 at 09:13:55AM +0200, Laszlo Ersek wrote:
>> Another style point / simplification has occurred to me the other day
>> too: in the patch I use the following expression four times:
>>
>>   ([ device_model ] @ common_props)
>>
>> that should be just
>>
>>   (device_model :: common_props)
>
> The second one is more efficient too.  I just checked and ocamlopt
> 4.13.1 can't optimise the first one at all, there's still an explicit
> call to camlStdlib__$40 (@).  The second one just allocates a cons
> cell inline.
>
> Rich.
>

Merged as commit 8643970f9791 (after retesting), with the following diff
squashed:

diff --git a/output/output_qemu.ml b/output/output_qemu.ml
index da8bd475e56e..f5e43705d101 100644
--- a/output/output_qemu.ml
+++ b/output/output_qemu.ml
@@ -197,7 +197,8 @@ module QEMU = struct
     and floppy_filter =
       function
       | BusSlotRemovable { s_removable_type = Floppy } -> true
-      | _ -> false in
+      | _ -> false
+    in
     let ide_ctrl_needed =
       Array.exists disk_cdrom_filter target_buses.target_ide_bus
     and scsi_ctrl_needed =
@@ -261,7 +262,8 @@ module QEMU = struct
     and add_floppy_backend backend_name =
       (* Add a drive (back-end) for a "floppy" device (front-end). The drive is
        * empty -- there is no backing file. *)
-      arg_list "-drive" [ "if=none"; "id=" ^ backend_name; "media=disk" ] in
+      arg_list "-drive" [ "if=none"; "id=" ^ backend_name; "media=disk" ]
+    in

     let add_virtio_blk disk_id frontend_ctr =
       (* Create a "virtio-blk-pci" device (front-end), together with its drive
@@ -289,10 +291,10 @@ module QEMU = struct
       (match disk_id with
        | Some id ->
            add_disk_backend id backend_name;
-           arg_list "-device" ([ "ide-hd" ] @ common_props)
+           arg_list "-device" ("ide-hd" :: common_props)
        | None ->
            add_cdrom_backend backend_name;
-           arg_list "-device" ([ "ide-cd" ] @ common_props))
+           arg_list "-device" ("ide-cd" :: common_props))

     and add_scsi disk_id frontend_ctr =
       (* Create a "scsi-hd" or "scsi-cd" device (front-end), together with its
@@ -307,10 +309,10 @@ module QEMU = struct
       (match disk_id with
        | Some id ->
            add_disk_backend id backend_name;
-           arg_list "-device" ([ "scsi-hd" ] @ common_props)
+           arg_list "-device" ("scsi-hd" :: common_props)
        | None ->
            add_cdrom_backend backend_name;
-           arg_list "-device" ([ "scsi-cd" ] @ common_props))
+           arg_list "-device" ("scsi-cd" :: common_props))

     and add_floppy frontend_ctr =
       (* Create a "floppy" (front-end), together with its empty drive
@@ -320,7 +322,8 @@ module QEMU = struct
       add_floppy_backend backend_name;
       arg_list "-device" [ "floppy"; "bus=floppy-bus.0";
                            sprintf "unit=%d" frontend_ctr;
-                           "drive=" ^ backend_name ] in
+                           "drive=" ^ backend_name ]
+    in

     (* Add virtio-blk-pci devices for BusSlotDisk elements on
      * "target_virtio_blk_bus".
@@ -339,7 +342,8 @@ module QEMU = struct
           bus_adder (Some d.s_disk_id) frontend_ctr
       | BusSlotRemovable { s_removable_type = CDROM } ->
           bus_adder None frontend_ctr
-      | _ -> () in
+      | _ -> ()
+    in

     (* Add disks and CD-ROMs to the IDE and SCSI buses. *)
     Array.iteri (add_disk_or_cdrom add_ide) target_buses.target_ide_bus;

Thanks
Laszlo