[Qemu-devel] [PATCH v3 8/9] vmstate: Add preallocation for migrating arrays (VMS_ALLOC flag)

[Alexey Kardashevskiy]

There are few helpers already to support array migration. However they all
require the destination side to preallocate arrays before migration which
is not always possible due to unknown array size as it might be some
sort of dynamic state. One of the examples is an array of MSIX-enabled
devices in SPAPR PHB - this array may vary from 0 to 65536 entries and
its size depends on guest's ability to enable MSIX or do PCI hotplug.

This adds new VMSTATE_VARRAY_STRUCT_ALLOC macro which is pretty similar to
VMSTATE_STRUCT_VARRAY_POINTER_INT32 but it can alloc memory for migratign
array on the destination side.

This defines VMS_ALLOC flag for a field.

This changes vmstate_base_addr() to do the allocation when receiving
migration.

Signed-off-by: Alexey Kardashevskiy <address@hidden>
---
 include/migration/vmstate.h | 11 +++++++++++
 vmstate.c                   | 13 ++++++++++---
 2 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 7e45048..e794694 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -101,6 +101,7 @@ enum VMStateFlags {
     VMS_VARRAY_UINT8     = 0x400,  /* Array with size in uint8_t field*/
     VMS_VARRAY_UINT32    = 0x800,  /* Array with size in uint32_t field*/
     VMS_MUST_EXIST       = 0x1000, /* Field must exist in input */
+    VMS_ALLOC            = 0x2000, /* Alloc a buffer on the destination */
 };
 
 typedef struct {
@@ -429,6 +430,16 @@ extern const VMStateInfo vmstate_info_bitmap;
     .offset     = offsetof(_state, _field),                          \
 }
 
+#define VMSTATE_STRUCT_VARRAY_ALLOC(_field, _state, _field_num, _version, 
_vmsd, _type) {\
+    .name       = (stringify(_field)),                               \
+    .version_id = (_version),                                        \
+    .vmsd       = &(_vmsd),                                          \
+    .num_offset = vmstate_offset_value(_state, _field_num, int32_t), \
+    .size       = sizeof(_type),                                     \
+    .flags      = VMS_STRUCT|VMS_VARRAY_INT32|VMS_ALLOC|VMS_POINTER, \
+    .offset     = vmstate_offset_pointer(_state, _field, _type),     \
+}
+
 #define VMSTATE_STATIC_BUFFER(_field, _state, _version, _test, _start, _size) 
{ \
     .name         = (stringify(_field)),                             \
     .version_id   = (_version),                                      \
diff --git a/vmstate.c b/vmstate.c
index b5882fa..fb95e39 100644
--- a/vmstate.c
+++ b/vmstate.c
@@ -43,11 +43,18 @@ static int vmstate_size(void *opaque, VMStateField *field)
     return size;
 }
 
-static void *vmstate_base_addr(void *opaque, VMStateField *field)
+static void *vmstate_base_addr(void *opaque, VMStateField *field, bool alloc)
 {
     void *base_addr = opaque + field->offset;
 
     if (field->flags & VMS_POINTER) {
+        if (alloc && (field->flags & VMS_ALLOC)) {
+            int n_elems = vmstate_n_elems(opaque, field);
+            if (n_elems) {
+                *((void **)base_addr + field->start) = g_malloc_n(n_elems,
+                                                                  field->size);
+            }
+        }
         base_addr = *(void **)base_addr + field->start;
     }
 
@@ -81,7 +88,7 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription 
*vmsd,
              field->field_exists(opaque, version_id)) ||
             (!field->field_exists &&
              field->version_id <= version_id)) {
-            void *base_addr = vmstate_base_addr(opaque, field);
+            void *base_addr = vmstate_base_addr(opaque, field, true);
             int i, n_elems = vmstate_n_elems(opaque, field);
             int size = vmstate_size(opaque, field);
 
@@ -131,7 +138,7 @@ void vmstate_save_state(QEMUFile *f, const 
VMStateDescription *vmsd,
     while (field->name) {
         if (!field->field_exists ||
             field->field_exists(opaque, vmsd->version_id)) {
-            void *base_addr = vmstate_base_addr(opaque, field);
+            void *base_addr = vmstate_base_addr(opaque, field, false);
             int i, n_elems = vmstate_n_elems(opaque, field);
             int size = vmstate_size(opaque, field);
 
-- 
2.0.0