hvm: infrastructure for backwards-compatible loading

The hvm_save code is used to save and restore hypervisor-related hvm
state, either for classic save/restore, or for migration (including
remus).  This is meant to be backwards-compatible across some
hypervisor versions; but if it does change, there is no way to handle
the old format as well as the new.

This patch introduces the infrastructure to allow a single older
version ("compat") of any given "save type" to be defined, along with
a function to turn the "old" version into the "new" version.  If the
size check fails for the "normal" version, it will check the "compat"
version, and if it matches, will read the old entry and call the
conversion function.

This patch involves some preprocessor hackery, but I'm only extending
the hackery that's already there.

Signed-off-by: George Dunlap <george.dunlap@eu.citrix.com>
Acked-by: Tim Deegan <Tim.Deegan@citrix.com>
Committed-by: Tim Deegan <Tim.Deegan@citrix.com>
xen-unstable changeset:   23171:6a5830de7b54
xen-unstable date:        Wed Apr 06 11:40:51 2011 +0100

diff --git a/xen/include/public/hvm/save.h b/xen/include/public/hvm/save.h
index d45f0c1115cabb97fbda6b160ea827c0e383e3e3..8a4c53815a67cae0cef01d8cf4f79eb49d87ee3a 100644 (file)
--- a/xen/include/public/hvm/save.h
+++ b/xen/include/public/hvm/save.h
@@ -61,13 +61,35 @@ struct hvm_save_descriptor {
  * ugliness.
  */
 
-#define DECLARE_HVM_SAVE_TYPE(_x, _code, _type)                   \
-  struct __HVM_SAVE_TYPE_##_x { _type t; char c[_code]; }
+#ifdef __XEN__
+# define DECLARE_HVM_SAVE_TYPE_COMPAT(_x, _code, _type, _ctype, _fix)     \
+    static inline int __HVM_SAVE_FIX_COMPAT_##_x(void *h) { return _fix(h); } \
+    struct __HVM_SAVE_TYPE_##_x { _type t; char c[_code]; char cpt[2];}; \
+    struct __HVM_SAVE_TYPE_COMPAT_##_x { _ctype t; }                   
+
+# define DECLARE_HVM_SAVE_TYPE(_x, _code, _type)                         \
+    static inline int __HVM_SAVE_FIX_COMPAT_##_x(void *h) { BUG(); return -1; } \
+    struct __HVM_SAVE_TYPE_##_x { _type t; char c[_code]; char cpt[1];}; \
+    struct __HVM_SAVE_TYPE_COMPAT_##_x { _type t; }                   
+#else
+# define DECLARE_HVM_SAVE_TYPE_COMPAT(_x, _code, _type, _ctype, _fix)     \
+    struct __HVM_SAVE_TYPE_##_x { _type t; char c[_code]; char cpt[2];} 
+
+# define DECLARE_HVM_SAVE_TYPE(_x, _code, _type)                         \
+    struct __HVM_SAVE_TYPE_##_x { _type t; char c[_code]; char cpt[1];} 
+#endif
 
 #define HVM_SAVE_TYPE(_x) typeof (((struct __HVM_SAVE_TYPE_##_x *)(0))->t)
 #define HVM_SAVE_LENGTH(_x) (sizeof (HVM_SAVE_TYPE(_x)))
 #define HVM_SAVE_CODE(_x) (sizeof (((struct __HVM_SAVE_TYPE_##_x *)(0))->c))
 
+#ifdef __XEN__
+# define HVM_SAVE_TYPE_COMPAT(_x) typeof (((struct __HVM_SAVE_TYPE_COMPAT_##_x *)(0))->t)
+# define HVM_SAVE_LENGTH_COMPAT(_x) (sizeof (HVM_SAVE_TYPE_COMPAT(_x)))
+
+# define HVM_SAVE_HAS_COMPAT(_x) (sizeof (((struct __HVM_SAVE_TYPE_##_x *)(0))->cpt)-1)
+# define HVM_SAVE_FIX_COMPAT(_x, _dst) __HVM_SAVE_FIX_COMPAT_##_x(_dst)
+#endif
 
 /* 
  * The series of save records is teminated by a zero-type, zero-length 

diff --git a/xen/include/xen/hvm/save.h b/xen/include/xen/hvm/save.h
index 512311fd5598640d38b45850c26e75896dc6bf43..43adfcf39c621b4aca22fd221c28484a03c9c896 100644 (file)
--- a/xen/include/xen/hvm/save.h
+++ b/xen/include/xen/hvm/save.h
@@ -58,13 +58,19 @@ void _hvm_read_entry(struct hvm_domain_context *h,
  * Unmarshalling: check, then copy. Evaluates to zero on success. This load
  * function requires the save entry to be the same size as the dest structure.
  */
-#define _hvm_load_entry(_x, _h, _dst, _strict) ({               \
-    int r;                                                      \
-    r = _hvm_check_entry((_h), HVM_SAVE_CODE(_x),               \
-                         HVM_SAVE_LENGTH(_x), (_strict));       \
-    if ( r == 0 )                                               \
-        _hvm_read_entry((_h), (_dst), HVM_SAVE_LENGTH(_x));     \
+#define _hvm_load_entry(_x, _h, _dst, _strict) ({                       \
+    int r;                                                              \
+    if ( (r = _hvm_check_entry((_h), HVM_SAVE_CODE(_x),                 \
+               HVM_SAVE_LENGTH(_x), (_strict))) == 0 )                  \
+        _hvm_read_entry((_h), (_dst), HVM_SAVE_LENGTH(_x));             \
+    else if (HVM_SAVE_HAS_COMPAT(_x)                                    \
+             && (r = _hvm_check_entry((_h), HVM_SAVE_CODE(_x),          \
+                       HVM_SAVE_LENGTH_COMPAT(_x), (_strict))) == 0 ) { \
+        _hvm_read_entry((_h), (_dst), HVM_SAVE_LENGTH_COMPAT(_x));      \
+        r=HVM_SAVE_FIX_COMPAT(_x, (_dst));                              \
+    }                                                                   \
     r; })
+
 #define hvm_load_entry(_x, _h, _dst)            \
     _hvm_load_entry(_x, _h, _dst, 1)
 #define hvm_load_entry_zeroextend(_x, _h, _dst) \