[PATCH 03/11] vmstate: Do not set size for VMS_ARRAY_OF_POINTER

[Peter Xu <peterx@redhat.com>]

When VMS_ARRAY_OF_POINTER is specified, it means the vmstate field is an
array of pointers.

The size of the element is not relevant to whatever it is stored inside: it
is always the host pointer size.

Let's reserve the "size" field in this case for future use, update
vmstate_size() so as to make it still work for array of pointers properly.

When at this, provide rich documentation on how size / size_offset works in
vmstate.

Reviewed-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@futurfusion.io>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 include/migration/vmstate.h | 20 ++++++++++++++++----
 migration/savevm.c          |  3 +++
 migration/vmstate.c         | 10 +++++++++-
 3 files changed, 28 insertions(+), 5 deletions(-)

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 32bb8e8ebc..350e62a55a 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -183,11 +183,26 @@ typedef enum {
 struct VMStateField {
     const char *name;
     size_t offset;
+
+    /*
+     * @size or @size_offset specifies the size of the element embeded in
+     * the field.  Only one of them should be present never both.  When
+     * @size_offset is used together with VMS_VBUFFER, it means the size is
+     * dynamic calculated instead of a constant.
+     *
+     * When the field is an array of any type, this stores the size of one
+     * element of the array.
+     *
+     * NOTE: even if VMS_POINTER or VMS_ARRAY_OF_POINTER may be specified,
+     * this parameter always reflects the real size of the objects that a
+     * pointer point to.
+     */
     size_t size;
+    size_t size_offset;
+
     size_t start;
     int num;
     size_t num_offset;
-    size_t size_offset;
     const VMStateInfo *info;
     enum VMStateFlags flags;
     const VMStateDescription *vmsd;
@@ -547,7 +562,6 @@ extern const VMStateInfo vmstate_info_qlist;
     .version_id = (_version),                                        \
     .num        = (_num),                                            \
     .info       = &(_info),                                          \
-    .size       = sizeof(_type *),                                   \
     .flags      = VMS_ARRAY|VMS_ARRAY_OF_POINTER,                    \
     .offset     = vmstate_offset_array(_state, _field, _type *, _num), \
 }
@@ -557,7 +571,6 @@ extern const VMStateInfo vmstate_info_qlist;
     .version_id = (_v),                                              \
     .num        = (_n),                                              \
     .vmsd       = &(_vmsd),                                          \
-    .size       = sizeof(_type *),                                    \
     .flags      = VMS_ARRAY|VMS_STRUCT|VMS_ARRAY_OF_POINTER,         \
     .offset     = vmstate_offset_array(_s, _f, _type*, _n),          \
 }
@@ -567,7 +580,6 @@ extern const VMStateInfo vmstate_info_qlist;
     .version_id = (_version),                                             \
     .num_offset = vmstate_offset_value(_state, _field_num, uint32_t),     \
     .info       = &(_info),                                               \
-    .size       = sizeof(_type *),                                          \
     .flags      = VMS_VARRAY_UINT32 | VMS_ARRAY_OF_POINTER | VMS_POINTER, \
     .offset     = vmstate_offset_pointer(_state, _field, _type *),          \
 }
diff --git a/migration/savevm.c b/migration/savevm.c
index 8115203b51..f5a6fd0c66 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -868,6 +868,9 @@ static void vmstate_check(const VMStateDescription *vmsd)
 
     if (field) {
         while (field->name) {
+            if (field->flags & VMS_ARRAY_OF_POINTER) {
+                assert(field->size == 0);
+            }
             if (field->flags & (VMS_STRUCT | VMS_VSTRUCT)) {
                 /* Recurse to sub structures */
                 vmstate_check(field->vmsd);
diff --git a/migration/vmstate.c b/migration/vmstate.c
index e98b5f5346..e29a8c3f49 100644
--- a/migration/vmstate.c
+++ b/migration/vmstate.c
@@ -110,13 +110,21 @@ static int vmstate_n_elems(void *opaque, const VMStateField *field)
 
 static int vmstate_size(void *opaque, const VMStateField *field)
 {
-    int size = field->size;
+    int size;
 
     if (field->flags & VMS_VBUFFER) {
         size = *(int32_t *)(opaque + field->size_offset);
         if (field->flags & VMS_MULTIPLY) {
             size *= field->size;
         }
+    } else if (field->flags & VMS_ARRAY_OF_POINTER) {
+        /*
+         * For an array of pointer, the each element is always size of a
+         * host pointer.
+         */
+        size = sizeof(void *);
+    } else {
+        size = field->size;
     }
 
     return size;
-- 
2.50.1