libxl: pvh: Add accessor macros for domain-type and -version dependent fields

We are going to have some fields whose location now depends in a
complicated way on the domain type, the Xen release, and the Meltdown
patch status.

Introduce some macros to help access these fields.  Currently they
don't do very much interesting because we don't have the PVH guest
type.

And nothing uses them yet, so no functional change in this patch.

Signed-off-by: Ian Jackson <Ian.Jackson@eu.citrix.com>

diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index acbf47690e85b6f80465d885c995b8b9b126a366..0064db94afbfc6ea1118e522da27d18af1fd4825 100644 (file)
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -287,6 +287,98 @@
  */
 #define LIBXL_HAVE_SCHED_CREDIT2_PARAMS 1
 
+/*
+ * LIBXL_BUILDINFO_SUBFIELD_PVH     #defined to simply   u.pvh.  or empty
+ * LIBXL_BUILDINFO_SUBFIELD_PV      #defined to simply   u.pv.   or empty
+ * LIBXL_BUILDINFO_SUBFIELD_HVM     #defined to simply   u.hvm.  or empty
+ *
+ * int LIBXL_BUILDINFO_ACCESS_PVH_{PV,HVM}_OK(
+ *                 libxl_domain_build_info *b_info,
+ *            )
+ * field_type *LIBXL_BUILDINFO_ACCESS_PVH_{PV,HVM}(
+ *                 libxl_domain_build_info *b_info,
+ *                 field_name
+ *            )
+ *
+ * Maybe used to access these fields of libxl_domain_build_info
+ *
+ *     Xen 4.9 and earlier      Xen <= 4.9        Xen 4.10 and later
+ *      HVM and PV guests        PVH guests        all guests
+ *
+ *       .u.pv.bootloader        .u.pvh.bootloader         .bootloader
+ *       .u.pv.bootloader_args   .u.pvh.bootloader_args    .bootloader_args
+ *       .u.hvm.timer_mode       .u.pvh.timer_mode         .timer_mode
+ *       .u.hvm.apic             .u.pvh.apic               .apic
+ *       .u.hvm.nested_hvm       .u.pvh.nested_hvm         .nested_hvm
+ *
+ *     [1] introduced, like this macro, in the PVH backport series
+ #       for Meltdown.
+ *
+ * _SUBFIELD_FOO can be used when the guest type is known to be FOO
+ * (specifically, when b_info->type is LIBXL_DOMAIN_TYPE_FOO)
+ *
+ * _ACCESS_PVH_FOO should be used for fields which were in .u.foo,
+ * at points in the code where the guest type is not fully known.
+ * It is only safe to evaluate if the guest type is PVH or FOO.
+ * This can be checked with _ACCESS_PVH_FOO_OK.
+ *
+ * We recommend the folllowing idiom:
+ *
+ *    #if defined(LIBXL_BUILDINFO_PVH_ACCESS_PVH_HVM) // post-Meltdown
+ *    # define U_PV_OK( b) LIBXL_BUILDINFO_ACCESS_PVH_PV_OK( (b))
+ *    # define U_HVM_OK(b) LIBXL_BUILDINFO_ACCESS_PVH_HVM_OK((b))
+ *    # define U_PV_F( b, f) LIBXL_BUILDINFO_ACCESS_PVH_PV( (b),f)
+ *    # define U_HVM_F(b, f) LIBXL_BUILDINFO_ACCESS_PVH_HVM((b),f)
+ *    # define U_PVH LIBXL_BUILDINFO_SUBFIELD_PVH
+ *    # define U_PV  LIBXL_BUILDINFO_SUBFIELD_PV
+ *    # define U_HVM LIBXL_BUILDINFO_SUBFIELD_HVM
+ #    #elif defined(LIBXL_HAVE_BUILDINFO_APIC) // >= 4.10 pre-Meltdown
+ *    # define U_PV_OK( b) 1
+ *    # define U_HVM_OK(b) 1
+ *    # define U_PV_F( b, f) (&(b)->f)
+ *    # define U_HVM_F(b, f) (&(b)->f)
+ *    * define U_PVH // empty
+ *    * define U_PV  // empty
+ *    * define U_HVM // empty
+ *    #else // Xen <= 4.9 pre-Meltdown
+ #    # define U_PV_OK( b) ((b)->type == LIBXL_DOMAIN_TYPE_PV )
+ #    # define U_HVM_OK(b) ((b)->type == LIBXL_DOMAIN_TYPE_HVM)
+ *    # define U_PV_F( b, f) (&(b)->u.pv .f)
+ *    # define U_HVM_F(b, f) (&(b)->u.hvm.f)
+ *    # define U_PVH UNAVAILABLE_BECAUSE_NO_PVH_SUPPORT_XEN_TOO_OLD
+ *    # define U_PV  u.pv.
+ *    # define U_HVM u.hvm.
+ *    #endif
+ *
+ * And then something like this:
+ *
+ *     if (U_HVM_OK(b_info))
+ *         libxl_defbool_set(U_HVM(b_info, apic), 1);
+ *
+ *     case LIBXL_DOMAIN_TYPE_PV:
+ *         if (b_info->U_PV bootloader) {
+ */
+
+#define LIBXL_BUILDINFO_ACCESS_PVH_PV(b_info, field_name)               \
+  ((b_info)->type == LIBXL_DOMAIN_TYPE_PV  ? &(b_info)->u.pv .field_name : \
+   (abort(), (typeof(&(b_info)->u.pv. field_name))0))
+
+#define LIBXL_BUILDINFO_ACCESS_PVH_HVM(b_info, field_name)              \
+  ((b_info)->type == LIBXL_DOMAIN_TYPE_HVM ? &(b_info)->u.hvm.field_name : \
+   (abort(), (typeof(&(b_info)->u.hvm.field_name))0))
+
+#define LIBXL_BUILDINFO_ACCESS_PVH_PV_OK(b_info, field_name)    \
+  ((b_info)->type == LIBXL_DOMAIN_TYPE_PV  ? 1 :               \
+   0)
+
+#define LIBXL_BUILDINFO_ACCESS_PVH_HVM_OK(b_info, field_name)   \
+  ((b_info)->type == LIBXL_DOMAIN_TYPE_HVM ? 1 :               \
+   0)
+
+#define LIBXL_BUILDINFO_SUBFIELD_PVH  UNAVAILABLE_BECAUSE_NO_PVH_SUPPORT_XEN_TOO_OLD
+#define LIBXL_BUILDINFO_SUBFIELD_PV   u.pv.
+#define LIBXL_BUILDINFO_SUBFIELD_HVM  u.hvm.
+
 /*
  * libxl ABI compatibility
  *