libxl: don't add cache mode for qdisk cdrom drives

qemu commit 91a097e7 forbids specifying cache mode for empty
drives. Attempting to create a domain with an empty qdisk cdrom
drive results in

qemu-system-x86_64: -drive if=ide,index=1,readonly=on,media=cdrom,
   cache=writeback,id=ide-832: Must specify either driver or file

libxl only allows an empty 'target=' for cdroms. By default, cdroms
are readonly (see the 'access' parameter in xl-disk-configuration.txt)
and forced to readonly by any tools (e.g. xl) using libxlutil's
xlu_disk_parse() function. With cdroms always marked readonly,
explicitly specifying the cache mode for cdrom drives can be dropped.
The drive's 'readonly=on' option can also be set unconditionally.

Signed-off-by: Jim Fehlig <jfehlig@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
index a1f7bd8aa36f1db08cc2fbe43385bd17dcbef809..4aff323acfae82514c0c9b3410f48b41e9315229 100644 (file)
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -1368,8 +1368,8 @@ static int libxl__build_device_model_args_new(libxl__gc *gc,
 
             if (disks[i].is_cdrom) {
                 drive = libxl__sprintf(gc,
-                         "if=ide,index=%d,readonly=%s,media=cdrom,cache=writeback,id=ide-%i",
-                         disk, disks[i].readwrite ? "off" : "on", dev_number);
+                         "if=ide,index=%d,readonly=on,media=cdrom,id=ide-%i",
+                         disk, dev_number);
 
                 if (target_path)
                     drive = libxl__sprintf(gc, "%s,file=%s,format=%s",