[XEN PATCH 4/8] libxl: Use -device for cd-rom drives

[Anthony PERARD <anthony.perard@xxxxxxxxxx>]

This allows to set an `id` on the device instead of only the drive. We
are going to need the `id` with the "eject" and
"blockdev-change-media" QMP command as using `device` parameter on
those is deprecated. (`device` is the `id` of the `-drive` on the
command line).

We set the same `id` on both -device and -drive as QEMU doesn't
complain and we can then either do "eject id=$id" or "eject
device=$id".

Using "-drive + -device" instead of only "-drive" has been
available since at least QEMU 0.15, and seems to be the preferred way as it
separates the host part (-drive which describe the disk image location
and format) from the guest part (-device which describe the emulated
device). More information in qemu.git/docs/qdev-device-use.txt .

Changing the command line during migration for the cdrom seems fine.
Also the documentation about migration in QEMU explains that the device
state ID is "been formed from a bus name and device address", so
second IDE bus and first device address on bus is still thus and
doesn't matter if written "-drive if=ide,index=2" or "-drive
ide-cd,bus=ide.1,unit=0".
See qemu.git/docs/devel/migration.rst .

Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
---
 tools/libs/light/libxl_dm.c | 16 +++++++++++++---
 1 file changed, 13 insertions(+), 3 deletions(-)

diff --git a/tools/libs/light/libxl_dm.c b/tools/libs/light/libxl_dm.c
index 0a0c1ef7c62e..5b01cf284163 100644
--- a/tools/libs/light/libxl_dm.c
+++ b/tools/libs/light/libxl_dm.c
@@ -1913,6 +1913,7 @@ static int libxl__build_device_model_args_new(libxl__gc 
*gc,
             }
 
             if (disks[i].is_cdrom) {
+                const char *drive_id;
                 if (disk > 4) {
                     LOGD(WARN, guest_domid, "Emulated CDROM can be only one of 
the first 4 disks.\n"
                          "Disk %s will be available via PV drivers but not as 
an "
@@ -1920,13 +1921,22 @@ static int libxl__build_device_model_args_new(libxl__gc 
*gc,
                          disks[i].vdev);
                     continue;
                 }
-                drive = libxl__sprintf(gc,
-                         "if=ide,index=%d,readonly=on,media=cdrom,id=ide-%i",
-                         disk, dev_number);
+
+                drive_id = GCSPRINTF("ide-%i", dev_number);
+                drive = GCSPRINTF("if=none,readonly=on,id=%s", drive_id);
 
                 if (target_path)
                     drive = libxl__sprintf(gc, "%s,file=%s,format=%s",
                                            drive, target_path, format);
+
+                flexarray_vappend(dm_args,
+                    "-drive", drive,
+                    "-device",
+                    GCSPRINTF("ide-cd,id=%s,drive=%s,bus=ide.%u,unit=%u",
+                              drive_id, drive_id,
+                              disk / 2, disk % 2),
+                    NULL);
+                continue;
             } else {
                 /*
                  * Explicit sd disks are passed through as is.
-- 
Anthony PERARD