Re: [PATCH 2/4] migration: Introduce VMStateOffset
Peter Xu <[email protected]> Fri, 31 Jul 2026 11:59:10 -0400
| Newsgroups | org.nongnu.qemu-devel |
|---|---|
| Message-ID | <[email protected]> |
On Fri, Jul 31, 2026 at 11:02:27AM -0300, Fabiano Rosas wrote:
> Hi Vladimir, I've been looking at this, could you clarify which vmstates
> do you think we could merge? I don't see it, either VARRAY vs. VBUFFER
> or VARRAY vs. BUFFER, also ARRAY vs. BUFFER doesn't seem to work.
>
> One main point of difference is the size_offset/num_offset variants are
> only known at load-time, so we can't convert them between each other at
> build time because the either the total size or num will not be know.
Something like this?
NOTE: I hid a fix to a comment that is irrelevant.. which I mentioned @size
and @size_offset can't co-exist, but it can when VMS_MULTIPLY is set. I
had a vague feeling we can further clean vmstate flags.
diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h
index 24631fd678..3a02709650 100644
--- a/include/migration/vmstate.h
+++ b/include/migration/vmstate.h
@@ -69,17 +69,15 @@ enum VMStateFlags {
* }). Dereference the pointer before using it as basis for
* further pointer arithmetic (see e.g. VMS_ARRAY). Does not
* affect the meaning of VMStateField.num_offset or
- * VMStateField.size_offset; see VMS_VARRAY and VMS_VBUFFER for
- * those.
+ * VMStateField.size_offset; see VMS_VARRAY for those.
*/
VMS_POINTER = 0x002,
/* The field is an array of fixed size. VMStateField.num contains
* the number of entries in the array. The size of each entry is
* given by VMStateField.size and / or opaque +
- * VMStateField.size_offset; see VMS_VBUFFER and
- * VMS_MULTIPLY. Each array entry will be processed individually
- * (VMStateField.info.get()/put() if VMS_STRUCT is not set,
+ * VMStateField.size_offset. Each array entry will be processed
+ * individually (VMStateField.info.get()/put() if VMS_STRUCT is not set,
* recursion into VMStateField.vmsd if VMS_STRUCT is set). May not
* be combined with VMS_VARRAY.
*/
@@ -108,18 +106,10 @@ enum VMStateFlags {
*/
VMS_ARRAY_OF_POINTER = 0x040,
- /* The size of the individual entries (a single array entry if
- * VMS_ARRAY or VMS_VARRAY are set, or the field itself if
- * neither is set) is variable (i.e. not known at compile-time),
- * but the same for all entries. Use the int32_t at opaque +
- * VMStateField.size_offset (subject to VMS_MULTIPLY) to determine
- * the size of each (and every) entry. */
- VMS_VBUFFER = 0x100,
-
/* Multiply the entry size given by the int32_t at opaque +
- * VMStateField.size_offset (see VMS_VBUFFER description) with
- * VMStateField.size to determine the number of bytes to be
- * allocated. Only valid in combination with VMS_VBUFFER. */
+ * VMStateField.size_offset with VMStateField.size to determine the
+ * number of bytes to be allocated.
+ */
VMS_MULTIPLY = 0x200,
/* Fail loading the serialised VM state if this field is missing
@@ -181,8 +171,8 @@ struct VMStateField {
/*
* @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
+ * the field. Only one of them should be present never both, except
+ * VMS_MULTIPLY. When @size_offset is used, 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
@@ -696,7 +686,7 @@ extern const VMStateInfo vmstate_info_g_byte_array;
.size_offset = vmstate_field_offset(_state, _field_size), \
.size = (_multiply), \
.info = &vmstate_info_buffer, \
- .flags = VMS_VBUFFER|VMS_POINTER|VMS_MULTIPLY, \
+ .flags = VMS_VARRAY|VMS_POINTER|VMS_MULTIPLY, \
.offset = offsetof(_state, _field), \
}
@@ -706,7 +696,7 @@ extern const VMStateInfo vmstate_info_g_byte_array;
.field_exists = (_test), \
.size_offset = vmstate_field_offset(_state, _field_size), \
.info = &vmstate_info_buffer, \
- .flags = VMS_VBUFFER|VMS_POINTER, \
+ .flags = VMS_VARRAY|VMS_POINTER, \
.offset = offsetof(_state, _field), \
}
@@ -720,7 +710,7 @@ extern const VMStateInfo vmstate_info_g_byte_array;
.field_exists = (_test), \
.size_offset = vmstate_field_offset(_state, _field_size), \
.info = &vmstate_info_buffer, \
- .flags = VMS_VBUFFER|VMS_POINTER|VMS_ALLOC, \
+ .flags = VMS_VARRAY|VMS_POINTER|VMS_ALLOC, \
.offset = offsetof(_state, _field), \
}
@@ -798,7 +788,7 @@ extern const VMStateInfo vmstate_info_g_byte_array;
.version_id = (_version), \
.size_offset = vmstate_field_offset(_state, _field_size), \
.info = &vmstate_info_bitmap, \
- .flags = VMS_VBUFFER|VMS_POINTER, \
+ .flags = VMS_VARRAY|VMS_POINTER, \
.offset = offsetof(_state, _field), \
}
@@ -1200,9 +1190,6 @@ extern const VMStateInfo vmstate_info_g_byte_array;
#define VMSTATE_BUFFER_START_MIDDLE(_f, _s, _start) \
VMSTATE_BUFFER_START_MIDDLE_V(_f, _s, _start, 0)
-#define VMSTATE_PARTIAL_VBUFFER(_f, _s, _size) \
- VMSTATE_VBUFFER(_f, _s, 0, NULL, _size)
-
#define VMSTATE_PARTIAL_VBUFFER_UINT32(_f, _s, _size) \
VMSTATE_VBUFFER_UINT32(_f, _s, 0, NULL, _size)
diff --git a/migration/vmstate.c b/migration/vmstate.c
index bc8eb3d3ca..f7363a8776 100644
--- a/migration/vmstate.c
+++ b/migration/vmstate.c
@@ -102,7 +102,7 @@ static uint64_t vmstate_n_elems(void *opaque, const VMStateField *field)
if (field->flags & VMS_ARRAY) {
n_elems = field->num;
- } else if (field->flags & VMS_VARRAY) {
+ } else if (field->num_offset.size) {
n_elems = vmstate_read_from_offset(opaque, &field->num_offset);
}
@@ -114,17 +114,17 @@ static uint64_t vmstate_size(void *opaque, const VMStateField *field)
{
uint64_t size;
- if (field->flags & VMS_VBUFFER) {
- size = vmstate_read_from_offset(opaque, &field->size_offset);
- if (field->flags & VMS_MULTIPLY) {
- size *= field->size;
- }
- } else if (field->flags & VMS_ARRAY_OF_POINTER) {
+ 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 if (field->size_offset.size) {
+ size = vmstate_read_from_offset(opaque, &field->size_offset);
+ if (field->flags & VMS_MULTIPLY) {
+ size *= field->size;
+ }
} else {
size = field->size;
}
--
2.54.0
--
Peter Xu