[Xen-devel] [PATCH v3 5/5] libxl: add domain config parameter to force start of qemu

[Juergen Gross <jgross@xxxxxxxx>]

Today the device model (qemu) is started for a pv domain only in case
a device requiring qemu is specified in the domain configuration
(qdisk, vfb, channel). If there is no such device the device model
isn't started and hence it is impossible to add such a device to the
domain later.

Add a domain configuration parameter to specify the device model is
to be started in any case. This will enable adding devices with a
qemu based backend later.

While the optimal solution would be to start the device model
automatically when needed this would require some major rework of
libxl at multiple places.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
 docs/man/xl.cfg.pod.5       | 6 ++++++
 tools/libxl/libxl_create.c  | 1 +
 tools/libxl/libxl_dm.c      | 5 +++++
 tools/libxl/libxl_types.idl | 1 +
 tools/libxl/xl_cmdimpl.c    | 3 +++
 5 files changed, 16 insertions(+)

diff --git a/docs/man/xl.cfg.pod.5 b/docs/man/xl.cfg.pod.5
index a4cc1b3..a3611a6 100644
--- a/docs/man/xl.cfg.pod.5
+++ b/docs/man/xl.cfg.pod.5
@@ -1956,6 +1956,12 @@ xen-qemudepriv-domid$domid or xen-qemudepriv-shared or 
root.
 Please note that running QEMU as non-root causes migration and PCI
 passthrough not to work properly.
 
+=item B<device_model_always=BOOLEAN>
+
+If true, start the device model for paravirtualized domains even if this isn't
+required according to the configured devices. This allows to add such devices
+later when the domain is already running.
+
 =back
 
 =head2 Keymaps
diff --git a/tools/libxl/libxl_create.c b/tools/libxl/libxl_create.c
index 0e2b0a0..52a0a2f 100644
--- a/tools/libxl/libxl_create.c
+++ b/tools/libxl/libxl_create.c
@@ -73,6 +73,7 @@ int libxl__domain_build_info_setdefault(libxl__gc *gc,
         return ERROR_INVAL;
     }
 
+    libxl_defbool_setdefault(&b_info->device_model_always, false);
     libxl_defbool_setdefault(&b_info->device_model_stubdomain, false);
 
     if (libxl_defbool_val(b_info->device_model_stubdomain) &&
diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
index 78c46674..87d454c 100644
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -2115,6 +2115,11 @@ int libxl__need_xenpv_qemu(libxl__gc *gc, 
libxl_domain_config *d_config)
     if (libxl__get_domid(gc, &domid))
         goto out;
 
+    if (libxl_defbool_val(d_config->b_info.device_model_always)) {
+        ret = 1;
+        goto out;
+    }
+
     if (d_config->num_vfbs > 0) {
         ret = 1;
         goto out;
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 304aa11..8ff9050 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -451,6 +451,7 @@ libxl_domain_build_info = Struct("domain_build_info",[
     ("device_model_ssidref", uint32),
     ("device_model_ssid_label", string),
     ("device_model_user", string),
+    ("device_model_always", libxl_defbool),
 
     # extra parameters pass directly to qemu, NULL terminated
     ("extra",            libxl_string_list),
diff --git a/tools/libxl/xl_cmdimpl.c b/tools/libxl/xl_cmdimpl.c
index a3610fc..0fdca73 100644
--- a/tools/libxl/xl_cmdimpl.c
+++ b/tools/libxl/xl_cmdimpl.c
@@ -2269,6 +2269,9 @@ skip_usbdev:
     }
 
     /* parse device model arguments, this works for pv, hvm and stubdom */
+    xlu_cfg_get_defbool (config, "device_model_always",
+                         &b_info->device_model_always, 0);
+
     if (!xlu_cfg_get_string (config, "device_model", &buf, 0)) {
         fprintf(stderr,
                 "WARNING: ignoring device_model directive.\n"
-- 
2.6.2


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