[RFC PATCH v1 11/17] vmstate: Introduce vmstate_first

[Fabiano Rosas <farosas@suse.de>]

The vmstate_save|load_vmsd[_v] functions do a bit of juggling of
pointers to allocate/dereference arrays. Introduce a getter for the
first field. Take field->flags into consideration and also allocate
memory when necessary.

Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
maybe we can soon have an iterator
---
 migration/vmstate.c | 67 +++++++++++++++++++++++++--------------------
 1 file changed, 38 insertions(+), 29 deletions(-)

diff --git a/migration/vmstate.c b/migration/vmstate.c
index 85e63305f6..ab7c6fa4ab 100644
--- a/migration/vmstate.c
+++ b/migration/vmstate.c
@@ -100,23 +100,31 @@ static int vmstate_size(void *opaque, const VMStateField *field)
     return size;
 }
 
-static void *vmstate_handle_alloc(void *ptr, const VMStateField *field,
-                                 int size, int n_elems)
+static void *vmstate_handle_alloc(void **ptr, int size, int n_elems)
 {
-    void *new = ptr;
+    size *= n_elems;
+    if (size) {
+        *ptr = g_malloc(size);
+    }
+
+    return *ptr;
+}
+
+static void *vmstate_first(void *opaque, const VMStateField *field,
+                           int size, int n, bool alloc)
+{
+    void **first = opaque + field->offset;
+
+    if (alloc) {
+        return vmstate_handle_alloc(first, size, n);
+    }
 
     if (field->flags & VMS_POINTER) {
-        if (field->flags & VMS_ALLOC) {
-            size *= n_elems;
-            if (size) {
-                new = g_malloc(size);
-                *(void **)ptr = new;
-            }
-        }
-        assert(new || !n_elems || !size);
-        return *(void **)ptr;
+        assert(first || !n || !size);
+        return *first;
     }
-    return new;
+
+    return first;
 }
 
 static bool vmstate_ptr_marker_load(QEMUFile *f, bool *load_field,
@@ -251,11 +259,12 @@ bool vmstate_load_vmsd(QEMUFile *f, const VMStateDescription *vmsd,
         trace_vmstate_load_state_field(vmsd->name, field->name, exists);
 
         if (exists) {
-            void *first_elem = opaque + field->offset;
+            void *head;
             int i, n_elems = vmstate_n_elems(opaque, field);
             int size = vmstate_size(opaque, field);
 
-            first_elem = vmstate_handle_alloc(first_elem, field, size, n_elems);
+            head = vmstate_first(opaque, field, size, n_elems,
+                                 field->flags & VMS_ALLOC);
 
             for (i = 0; i < n_elems; i++) {
                 /* If we will process the load of field? */
@@ -264,7 +273,7 @@ bool vmstate_load_vmsd(QEMUFile *f, const VMStateDescription *vmsd,
                 void *curr_elem;
 
                 if (field->flags & VMS_ARRAY_OF_POINTER) {
-                    void **array_elem = (void **)first_elem + i;
+                    void **array_elem = (void **)head + i;
                     bool use_dynamic_array =
                         field->flags & VMS_ARRAY_OF_POINTER_AUTO_ALLOC;
                     bool use_marker_field;
@@ -290,13 +299,13 @@ bool vmstate_load_vmsd(QEMUFile *f, const VMStateDescription *vmsd,
                              * need the object size, not entry size of the
                              * array.
                              */
-                            curr_elem = g_malloc0(field->size);
-                            /* Remember to update the root pointer! */
-                            *(void **)array_elem = curr_elem;
+                            assert(!curr_elem);
+                            curr_elem = vmstate_handle_alloc(array_elem,
+                                                             field->size, 1);
                         }
                     }
                 } else {
-                    curr_elem = first_elem + size * i;
+                    curr_elem = head + size * i;
                 }
 
                 if (load_field) {
@@ -627,28 +636,26 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd,
 
     while (field->name) {
         if (vmstate_field_exists(vmsd, field, opaque, version_id)) {
-            void *first_elem = opaque + field->offset;
+            void *head;
             int i, n_elems = vmstate_n_elems(opaque, field);
             int size = vmstate_size(opaque, field);
             bool is_null_prev = false;
             bool use_vmdesc = true;
 
             trace_vmstate_save_state_loop(vmsd->name, field->name, n_elems);
-            if (field->flags & VMS_POINTER) {
-                first_elem = *(void **)first_elem;
-                assert(first_elem || !n_elems || !size);
-            }
+            head = vmstate_first(opaque, field, size, n_elems, false);
 
             for (i = 0; i < n_elems; i++) {
                 bool save_field = true;
-                void *curr_elem = first_elem + size * i;
+                void *curr_elem;
                 int max_elems = n_elems - i;
 
                 if (field->flags & VMS_ARRAY_OF_POINTER) {
                     bool use_marker_field, is_null, use_dynamic_array;
+                    void **array_elem = (void **)head + i;
 
-                    assert(curr_elem);
-                    curr_elem = *(void **)curr_elem;
+                    assert(array_elem);
+                    curr_elem = *array_elem;
 
                     is_null = !curr_elem;
 
@@ -681,7 +688,7 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd,
                             use_vmdesc = true;
 
                             for (int j = i + 1; j < n_elems; j++) {
-                                void *elem = *(void **)(first_elem + size * j);
+                                void *elem = *(void **)(head + size * j);
                                 bool elem_is_null = !elem;
 
                                 if (is_null != elem_is_null) {
@@ -706,6 +713,8 @@ static bool vmstate_save_vmsd_v(QEMUFile *f, const VMStateDescription *vmsd,
 
                         save_field = !!curr_elem;
                     }
+                } else {
+                    curr_elem = head + size * i;
                 }
 
                 if (save_field) {
-- 
2.51.0