domctl: improve device assignment structure layout and use

Avoid needless gaps. Make flags field mandatory for all three
operations (and rename it to fit the intended future purpose of
possibly holding more than just one flag).

Also correct a typo in a related domctl.h comment.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
The domain ID treatment of test_assign_device is at least strange:
Callers pass in a value, but do_domctl() as well as the actual handler
code ignore them. I think we should increase flexibility here by making
e.g. DOMID_INVALID a wild card to obtain current behavior, while
allowing individual domain IDs to be passed in to inquire whether the
device is assigned to that specific domain.

--- a/tools/libxc/xc_domain.c
+++ b/tools/libxc/xc_domain.c
@@ -1488,7 +1488,7 @@ int xc_assign_device(
     xc_interface *xch,
     uint32_t domid,
     uint32_t machine_sbdf,
-    uint32_t flag)
+    uint32_t flags)
 {
     DECLARE_DOMCTL;
 
@@ -1496,7 +1496,7 @@ int xc_assign_device(
     domctl.domain = domid;
     domctl.u.assign_device.dev = XEN_DOMCTL_DEV_PCI;
     domctl.u.assign_device.u.pci.machine_sbdf = machine_sbdf;
-    domctl.u.assign_device.flag = flag;
+    domctl.u.assign_device.flags = flags;
 
     return do_domctl(xch, &domctl);
 }
@@ -1547,6 +1547,7 @@ int xc_test_assign_device(
     domctl.domain = domid;
     domctl.u.assign_device.dev = XEN_DOMCTL_DEV_PCI;
     domctl.u.assign_device.u.pci.machine_sbdf = machine_sbdf;
+    domctl.u.assign_device.flags = 0;
 
     return do_domctl(xch, &domctl);
 }
@@ -1562,6 +1563,7 @@ int xc_deassign_device(
     domctl.domain = domid;
     domctl.u.assign_device.dev = XEN_DOMCTL_DEV_PCI;
     domctl.u.assign_device.u.pci.machine_sbdf = machine_sbdf;
+    domctl.u.assign_device.flags = 0;
 
     return do_domctl(xch, &domctl);
 }
@@ -1588,7 +1590,7 @@ int xc_assign_dt_device(
      * DT doesn't own any RDM so actually DT has nothing to do
      * for any flag and here just fix that as 0.
      */
-    domctl.u.assign_device.flag = 0;
+    domctl.u.assign_device.flags = 0;
     set_xen_guest_handle(domctl.u.assign_device.u.dt.path, path);
 
     rc = do_domctl(xch, &domctl);
@@ -1617,6 +1619,7 @@ int xc_test_assign_dt_device(
     domctl.u.assign_device.dev = XEN_DOMCTL_DEV_DT;
     domctl.u.assign_device.u.dt.size = size;
     set_xen_guest_handle(domctl.u.assign_device.u.dt.path, path);
+    domctl.u.assign_device.flags = 0;
 
     rc = do_domctl(xch, &domctl);
 
@@ -1644,6 +1646,7 @@ int xc_deassign_dt_device(
     domctl.u.assign_device.dev = XEN_DOMCTL_DEV_DT;
     domctl.u.assign_device.u.dt.size = size;
     set_xen_guest_handle(domctl.u.assign_device.u.dt.path, path);
+    domctl.u.assign_device.flags = 0;
 
     rc = do_domctl(xch, &domctl);
 
--- a/xen/drivers/passthrough/device_tree.c
+++ b/xen/drivers/passthrough/device_tree.c
@@ -147,11 +147,9 @@ int iommu_do_dt_domctl(struct xen_domctl
         if ( domctl->u.assign_device.dev != XEN_DOMCTL_DEV_DT )
             break;
 
-        if ( unlikely(d->is_dying) )
-        {
-            ret = -EINVAL;
+        ret = -EINVAL;
+        if ( d->is_dying || domctl->u.assign_device.flags )
             break;
-        }
 
         ret = dt_find_node_by_gpath(domctl->u.assign_device.u.dt.path,
                                     domctl->u.assign_device.u.dt.size,
@@ -176,6 +174,10 @@ int iommu_do_dt_domctl(struct xen_domctl
         if ( domctl->u.assign_device.dev != XEN_DOMCTL_DEV_DT )
             break;
 
+        ret = -EINVAL;
+        if ( domctl->u.assign_device.flags )
+            break;
+
         ret = dt_find_node_by_gpath(domctl->u.assign_device.u.dt.path,
                                     domctl->u.assign_device.u.dt.size,
                                     &dev);
@@ -197,6 +199,10 @@ int iommu_do_dt_domctl(struct xen_domctl
         if ( domctl->u.assign_device.dev != XEN_DOMCTL_DEV_DT )
             break;
 
+        ret = -EINVAL;
+        if ( domctl->u.assign_device.flags )
+            break;
+
         ret = dt_find_node_by_gpath(domctl->u.assign_device.u.dt.path,
                                     domctl->u.assign_device.u.dt.size,
                                     &dev);
--- a/xen/drivers/passthrough/pci.c
+++ b/xen/drivers/passthrough/pci.c
@@ -1540,12 +1540,13 @@ int iommu_do_pci_domctl(
 {
     u16 seg;
     u8 bus, devfn;
-    u32 flag;
     int ret = 0;
     uint32_t machine_sbdf;
 
     switch ( domctl->cmd )
     {
+        unsigned int flags;
+
     case XEN_DOMCTL_get_device_group:
     {
         u32 max_sdevs;
@@ -1583,6 +1584,10 @@ int iommu_do_pci_domctl(
         if ( domctl->u.assign_device.dev != XEN_DOMCTL_DEV_PCI )
             break;
 
+        ret = -EINVAL;
+        if ( domctl->u.assign_device.flags )
+            break;
+
         machine_sbdf = domctl->u.assign_device.u.pci.machine_sbdf;
 
         ret = xsm_test_assign_device(XSM_HOOK, machine_sbdf);
@@ -1614,11 +1619,10 @@ int iommu_do_pci_domctl(
         if ( domctl->u.assign_device.dev != XEN_DOMCTL_DEV_PCI )
             break;
 
-        if ( unlikely(d->is_dying) )
-        {
-            ret = -EINVAL;
+        ret = -EINVAL;
+        flags = domctl->u.assign_device.flags;
+        if ( d->is_dying || (flags & ~XEN_DOMCTL_DEV_RDM_RELAXED) )
             break;
-        }
 
         machine_sbdf = domctl->u.assign_device.u.pci.machine_sbdf;
 
@@ -1629,15 +1633,9 @@ int iommu_do_pci_domctl(
         seg = machine_sbdf >> 16;
         bus = PCI_BUS(machine_sbdf);
         devfn = PCI_DEVFN2(machine_sbdf);
-        flag = domctl->u.assign_device.flag;
-        if ( flag & ~XEN_DOMCTL_DEV_RDM_RELAXED )
-        {
-            ret = -EINVAL;
-            break;
-        }
 
         ret = device_assigned(seg, bus, devfn) ?:
-              assign_device(d, seg, bus, devfn, flag);
+              assign_device(d, seg, bus, devfn, flags);
         if ( ret == -ERESTART )
             ret = hypercall_create_continuation(__HYPERVISOR_domctl,
                                                 "h", u_domctl);
@@ -1661,6 +1659,10 @@ int iommu_do_pci_domctl(
         if ( domctl->u.assign_device.dev != XEN_DOMCTL_DEV_PCI )
             break;
 
+        ret = -EINVAL;
+        if ( domctl->u.assign_device.flags )
+            break;
+
         machine_sbdf = domctl->u.assign_device.u.pci.machine_sbdf;
 
         ret = xsm_deassign_device(XSM_HOOK, d, machine_sbdf);
--- a/xen/include/public/domctl.h
+++ b/xen/include/public/domctl.h
@@ -511,14 +511,17 @@ DEFINE_XEN_GUEST_HANDLE(xen_domctl_sendt
  * XEN_DOMCTL_deassign_device: The behavior of this DOMCTL differs
  * between the different type of device:
  *  - PCI device (XEN_DOMCTL_DEV_PCI) will be reassigned to DOM0
- *  - DT device (XEN_DOMCTL_DT_PCI) will left unassigned. DOM0
+ *  - DT device (XEN_DOMCTL_DEV_DT) will left unassigned. DOM0
  *  will have to call XEN_DOMCTL_assign_device in order to use the
  *  device.
  */
 #define XEN_DOMCTL_DEV_PCI      0
 #define XEN_DOMCTL_DEV_DT       1
 struct xen_domctl_assign_device {
+    /* IN */
     uint32_t dev;   /* XEN_DOMCTL_DEV_* */
+    uint32_t flags;
+#define XEN_DOMCTL_DEV_RDM_RELAXED      1 /* assign only */
     union {
         struct {
             uint32_t machine_sbdf;   /* machine PCI ID of assigned device */
@@ -528,9 +531,6 @@ struct xen_domctl_assign_device {
             XEN_GUEST_HANDLE_64(char) path; /* path to the device tree node */
         } dt;
     } u;
-    /* IN */
-#define XEN_DOMCTL_DEV_RDM_RELAXED      1
-    uint32_t  flag;   /* flag of assigned device */
 };
 typedef struct xen_domctl_assign_device xen_domctl_assign_device_t;
 DEFINE_XEN_GUEST_HANDLE(xen_domctl_assign_device_t);