[Xen-devel] [PATCH v3] libxl: make vkbd tunable for HVM guests

[Eslam Elnikety <elnikety@amazon.com>]

Each HVM guest currently gets a vkbd frontend/backend pair (c/s ebbd2561b4c).
This consumes host resources unnecessarily for guests that have no use for
vkbd. Make this behaviour tunable to allow an administrator to choose. The
commit retains the current behaviour -- HVM guests still get vkdb unless
specified otherwise.

Signed-off-by: Eslam Elnikety <elnikety@amazon.com>
---
    Changes in v2:
        - Added a missing hunk / setting vkb_device per config

    Changes in v3:
        - Added entries in libxl.h and in documentation
---
 docs/man/xl.cfg.pod.5.in    | 4 ++++
 tools/libxl/libxl.h         | 9 +++++++++
 tools/libxl/libxl_create.c  | 9 ++++++---
 tools/libxl/libxl_types.idl | 1 +
 tools/xl/xl_parse.c         | 1 +
 tools/xl/xl_sxp.c           | 2 ++
 6 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/docs/man/xl.cfg.pod.5.in b/docs/man/xl.cfg.pod.5.in
index 47d88243b1..c3641c7a57 100644
--- a/docs/man/xl.cfg.pod.5.in
+++ b/docs/man/xl.cfg.pod.5.in
@@ -2286,6 +2286,10 @@ devices are defined by the device model configuration, please see the
 B<qemu(1)> manpage for details. The default is not to export any sound
 device.
 
+=item B<vkb_device=BOOLEAN>
+
+Specifies that the HVM guest gets a vkdb. The default is true (1).
+
 =item B<usb=BOOLEAN>
 
 Enables or disables an emulated USB bus in the guest.
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index a09d069358..6884c1492a 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -616,6 +616,15 @@ typedef struct libxl__ctx libxl_ctx;
  */
 #define LIBXL_HAVE_BUILDINFO_VCPU_AFFINITY_ARRAYS 1
 
+/*
+ * LIBXL_HAVE_BUILDINFO_VKB_DEVICE
+ *
+ * If this is defined, then the libxl_domain_build_info structure will
+ * contain a boolean hvm.vkb_device which instructs libxl whether to include
+ * a vkbd at build time or not.
+ */
+#define LIBXL_HAVE_BUILDINFO_VKB_DEVICE 1
+
 /*
  * LIBXL_HAVE_BUILDINFO_USBDEVICE_LIST
  *
diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 5c9dd4cd21..8aecb9cfba 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -308,6 +308,7 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
         libxl_defbool_setdefault(&b_info->u.hvm.vpt_align,          true);
         libxl_defbool_setdefault(&b_info->u.hvm.altp2m,             false);
         libxl_defbool_setdefault(&b_info->u.hvm.usb,                false);
+        libxl_defbool_setdefault(&b_info->u.hvm.vkb_device,         true);
         libxl_defbool_setdefault(&b_info->u.hvm.xen_platform_pci,   true);
 
         libxl_defbool_setdefault(&b_info->u.hvm.spice.enable, false);
@@ -1393,9 +1394,11 @@ static void domcreate_launch_dm(libxl__egc *egc, libxl__multidev *multidev,
         libxl__device_console_add(gc, domid, &console, state, &device);
         libxl__device_console_dispose(&console);
 
-        libxl_device_vkb_init(&vkb);
-        libxl__device_add(gc, domid, &libxl__vkb_devtype, &vkb);
-        libxl_device_vkb_dispose(&vkb);
+        if (libxl_defbool_val(d_config->b_info.u.hvm.vkb_device)) {
+            libxl_device_vkb_init(&vkb);
+            libxl__device_add(gc, domid, &libxl__vkb_devtype, &vkb);
+            libxl_device_vkb_dispose(&vkb);
+        }
 
         dcs->sdss.dm.guest_domid = domid;
         if (libxl_defbool_val(d_config->b_info.device_model_stubdomain))
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 01ec1d1afa..1d436aa8bb 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -571,6 +571,7 @@ libxl_domain_build_info = Struct("domain_build_info",[
                                        # - "tablet" for absolute mouse,
                                        # - "mouse" for PS/2 protocol relative mouse
                                        ("usbdevice",        string),
+                                       ("vkb_device",       libxl_defbool),
                                        ("soundhw",          string),
                                        ("xen_platform_pci", libxl_defbool),
                                        ("usbdevice_list",   libxl_string_list),
diff --git a/tools/xl/xl_parse.c b/tools/xl/xl_parse.c
index e6c54483e0..37bc13bd83 100644
--- a/tools/xl/xl_parse.c
+++ b/tools/xl/xl_parse.c
@@ -2295,6 +2295,7 @@ skip_usbdev:
             fprintf(stderr,"xl: Unable to parse usbdevice.\n");
             exit(-ERROR_FAIL);
         }
+        xlu_cfg_get_defbool(config, "vkb_device", &b_info->u.hvm.vkb_device, 0);
         xlu_cfg_replace_string (config, "soundhw", &b_info->u.hvm.soundhw, 0);
         xlu_cfg_get_defbool(config, "xen_platform_pci",
                             &b_info->u.hvm.xen_platform_pci, 0);
diff --git a/tools/xl/xl_sxp.c b/tools/xl/xl_sxp.c
index 3e6117d0cd..359a001570 100644
--- a/tools/xl/xl_sxp.c
+++ b/tools/xl/xl_sxp.c
@@ -138,6 +138,8 @@ void printf_info_sexp(int domid, libxl_domain_config *d_config, FILE *fh)
         fprintf(fh, "\t\t\t(boot %s)\n", b_info->u.hvm.boot);
         fprintf(fh, "\t\t\t(usb %s)\n", libxl_defbool_to_string(b_info->u.hvm.usb));
         fprintf(fh, "\t\t\t(usbdevice %s)\n", b_info->u.hvm.usbdevice);
+        fprintf(fh, "\t\t\t(vkb_device %s)\n",
+               libxl_defbool_to_string(b_info->u.hvm.vkb_device));
         fprintf(fh, "\t\t)\n");
         break;
     case LIBXL_DOMAIN_TYPE_PV:
-- 
2.15.3.AMZN


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