[PATCH v2 6/6] libxc: make xc_domain_maximum_gpfn() endianness-agnostic

[Jan Beulich <jbeulich@xxxxxxxx>]

libxc generally uses uint32_t to represent domain IDs. This is fine as
long as addresses of such variables aren't taken, to then pass into
hypercalls: To the hypervisor, a domain ID is a 16-bit value. Introduce
a wrapper struct to deal with the issue. (On architectures with
arguments passed in registers, an intermediate variable would have been
created by the compiler already anyway, just one of the wrong type.)

The public interface change is both source and binary compatible for
the architectures we currently support.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
---
v2: Introduce wrapper struct in public interface.
---
Together with the comment change I was half tempted to also rename the
sub-function identifier to XENMEM_maximum_gfn. But I then decided this
would go too far here.

--- a/tools/libs/ctrl/xc_domain.c
+++ b/tools/libs/ctrl/xc_domain.c
@@ -856,7 +856,8 @@ int xc_domain_get_tsc_info(xc_interface
 
 int xc_domain_maximum_gpfn(xc_interface *xch, uint32_t domid, xen_pfn_t *gpfns)
 {
-    long rc = do_memory_op(xch, XENMEM_maximum_gpfn, &domid, sizeof(domid));
+    struct xen_memory_domain dom = { .domid = domid };
+    long rc = do_memory_op(xch, XENMEM_maximum_gpfn, &dom, sizeof(dom));
 
     if ( rc >= 0 )
     {
--- a/xen/common/memory.c
+++ b/xen/common/memory.c
@@ -1351,7 +1351,6 @@ long do_memory_op(unsigned long cmd, XEN
     long rc;
     struct xen_memory_reservation reservation;
     struct memop_args args;
-    domid_t domid;
     unsigned long start_extent = cmd >> MEMOP_EXTENT_SHIFT;
     int op = cmd & MEMOP_CMD_MASK;
 
@@ -1452,13 +1451,16 @@ long do_memory_op(unsigned long cmd, XEN
     case XENMEM_current_reservation:
     case XENMEM_maximum_reservation:
     case XENMEM_maximum_gpfn:
+    {
+        struct xen_memory_domain domain;
+
         if ( unlikely(start_extent) )
             return -EINVAL;
 
-        if ( copy_from_guest(&domid, arg, 1) )
+        if ( copy_from_guest(&domain, arg, 1) )
             return -EFAULT;
 
-        d = rcu_lock_domain_by_any_id(domid);
+        d = rcu_lock_domain_by_any_id(domain.domid);
         if ( d == NULL )
             return -ESRCH;
 
@@ -1486,6 +1488,7 @@ long do_memory_op(unsigned long cmd, XEN
         rcu_unlock_domain(d);
 
         break;
+    }
 
     case XENMEM_add_to_physmap:
     {
--- a/xen/include/public/memory.h
+++ b/xen/include/public/memory.h
@@ -148,16 +148,23 @@ DEFINE_XEN_GUEST_HANDLE(xen_memory_excha
  */
 #define XENMEM_maximum_ram_page     2
 
+struct xen_memory_domain {
+    /* [IN] Domain information is being queried for. */
+    domid_t domid;
+};
+
 /*
  * Returns the current or maximum memory reservation, in pages, of the
  * specified domain (may be DOMID_SELF). Returns -ve errcode on failure.
- * arg == addr of domid_t.
+ * arg == addr of struct xen_memory_domain.
  */
 #define XENMEM_current_reservation  3
 #define XENMEM_maximum_reservation  4
 
 /*
- * Returns the maximum GPFN in use by the guest, or -ve errcode on failure.
+ * Returns the maximum GFN in use by the specified domain (may be DOMID_SELF).
+ * Returns -ve errcode on failure.
+ * arg == addr of struct xen_memory_domain.
  */
 #define XENMEM_maximum_gpfn         14