[Qemu-devel] [PATCH 03/19] savevm: Implement VMS_DIVIDE flag

[Alexey Kardashevskiy <aik@ozlabs.ru>]

From: David Gibson <david@gibson.dropbear.id.au>

The vmstate infrastructure includes a VMS_MULTIPY flag, and associated
VMSTATE_VBUFFER_MULTIPLY helper macro.  These can be used to save a
variably sized buffer where the size in bytes of the buffer isn't directly
accessible as a structure field, but an element count from which the size
can be derived is.

This patch adds an analogous VMS_DIVIDE option, which handles a variably
sized buffer whose size is a submultiple of a field, rather than a
multiple.  For example a buffer containing per-page structures whose size
is derived from a field storing the total address space described by the
structures could use this construct.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
---
 include/migration/vmstate.h | 13 +++++++++++++
 savevm.c                    |  8 ++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 1c31b5d..672b0a7 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -100,6 +100,7 @@ enum VMStateFlags {
     VMS_MULTIPLY         = 0x200,  /* multiply "size" field by field_size */
     VMS_VARRAY_UINT8     = 0x400,  /* Array with size in uint8_t field*/
     VMS_VARRAY_UINT32    = 0x800,  /* Array with size in uint32_t field*/
+    VMS_DIVIDE           = 0x1000, /* divide "size" field by field_size */
 };
 
 typedef struct {
@@ -422,6 +423,18 @@ extern const VMStateInfo vmstate_info_bitmap;
     .start        = (_start),                                        \
 }
 
+#define VMSTATE_VBUFFER_DIVIDE(_field, _state, _version, _test, _start, _field_size, _divide) { \
+    .name         = (stringify(_field)),                             \
+    .version_id   = (_version),                                      \
+    .field_exists = (_test),                                         \
+    .size_offset  = vmstate_offset_value(_state, _field_size, uint32_t),\
+    .size         = (_divide),                                       \
+    .info         = &vmstate_info_buffer,                            \
+    .flags        = VMS_VBUFFER|VMS_POINTER|VMS_DIVIDE,              \
+    .offset       = offsetof(_state, _field),                        \
+    .start        = (_start),                                        \
+}
+
 #define VMSTATE_VBUFFER(_field, _state, _version, _test, _start, _field_size) { \
     .name         = (stringify(_field)),                             \
     .version_id   = (_version),                                      \
diff --git a/savevm.c b/savevm.c
index e0491e7..788af85 100644
--- a/savevm.c
+++ b/savevm.c
@@ -1700,6 +1700,10 @@ int vmstate_load_state(QEMUFile *f, const VMStateDescription *vmsd,
                 if (field->flags & VMS_MULTIPLY) {
                     size *= field->size;
                 }
+                if (field->flags & VMS_DIVIDE) {
+                    assert((size % field->size) == 0);
+                    size /= field->size;
+                }
             }
             if (field->flags & VMS_ARRAY) {
                 n_elems = field->num;
@@ -1764,6 +1768,10 @@ void vmstate_save_state(QEMUFile *f, const VMStateDescription *vmsd,
                 if (field->flags & VMS_MULTIPLY) {
                     size *= field->size;
                 }
+                if (field->flags & VMS_DIVIDE) {
+                    assert((size % field->size) == 0);
+                    size /= field->size;
+                }
             }
             if (field->flags & VMS_ARRAY) {
                 n_elems = field->num;
-- 
1.8.3.2