diff options
Diffstat (limited to 'include/migration/vmstate.h')
| -rw-r--r-- | include/migration/vmstate.h | 14 |
1 files changed, 14 insertions, 0 deletions
diff --git a/include/migration/vmstate.h b/include/migration/vmstate.h index a668ec75b8..9224370ed5 100644 --- a/include/migration/vmstate.h +++ b/include/migration/vmstate.h @@ -1035,6 +1035,20 @@ extern const VMStateInfo vmstate_info_qtailq; #define VMSTATE_BUFFER_UNSAFE(_field, _state, _version, _size) \ VMSTATE_BUFFER_UNSAFE_INFO(_field, _state, _version, vmstate_info_buffer, _size) +/* + * These VMSTATE_UNUSED*() macros can be used to fill in the holes + * when some of the vmstate fields are obsolete to be compatible with + * migrations between new/old binaries. + * + * CAUTION: when using any of the VMSTATE_UNUSED*() macros please be + * sure that the size passed in is the size that was actually *sent* + * rather than the size of the *structure*. One example is the + * boolean type - the size of the structure can vary depending on the + * definition of boolean, however the size we actually sent is always + * 1 byte (please refer to implementation of VMSTATE_BOOL_V and + * vmstate_info_bool). So here we should always pass in size==1 + * rather than size==sizeof(bool). + */ #define VMSTATE_UNUSED_V(_v, _size) \ VMSTATE_UNUSED_BUFFER(NULL, _v, _size) |