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[Qemu-devel] [PULL 01/16] migration: comment VMSTATE_UNUSED*() properly
From: |
Dr. David Alan Gilbert (git) |
Subject: |
[Qemu-devel] [PULL 01/16] migration: comment VMSTATE_UNUSED*() properly |
Date: |
Tue, 14 May 2019 19:34:39 +0100 |
From: Peter Xu <address@hidden>
It is error prone to use VMSTATE_UNUSED*() sometimes especially when
the size of the migration stream of the field is not the same as the
size of the structure (boolean is one example). Comment it well so
people will be aware of this when people want to use it.
Signed-off-by: Peter Xu <address@hidden>
Message-Id: <address@hidden>
Reviewed-by: Dr. David Alan Gilbert <address@hidden>
Signed-off-by: Dr. David Alan Gilbert <address@hidden>
---
include/migration/vmstate.h | 14 ++++++++++++++
1 file changed, 14 insertions(+)
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)
--
2.21.0
- [Qemu-devel] [PULL 00/16] migration queue, Dr. David Alan Gilbert (git), 2019/05/14
- [Qemu-devel] [PULL 01/16] migration: comment VMSTATE_UNUSED*() properly,
Dr. David Alan Gilbert (git) <=
- [Qemu-devel] [PULL 02/16] migration: not necessary to check ops again, Dr. David Alan Gilbert (git), 2019/05/14
- [Qemu-devel] [PULL 03/16] migration: remove not used field xfer_limit, Dr. David Alan Gilbert (git), 2019/05/14
- [Qemu-devel] [PULL 04/16] vmstate: check subsection_found is enough, Dr. David Alan Gilbert (git), 2019/05/14
- [Qemu-devel] [PULL 05/16] migration: savevm: fix error code with migration blockers, Dr. David Alan Gilbert (git), 2019/05/14
- [Qemu-devel] [PULL 06/16] migration/colo.c: Remove redundant input parameter, Dr. David Alan Gilbert (git), 2019/05/14
- [Qemu-devel] [PULL 07/16] migration/colo.h: Remove obsolete codes, Dr. David Alan Gilbert (git), 2019/05/14
- [Qemu-devel] [PULL 08/16] qemu-option.hx: Update missed parameter for colo-compare, Dr. David Alan Gilbert (git), 2019/05/14
- [Qemu-devel] [PULL 09/16] migration/ram.c: start of migration_bitmap_sync_range is always 0, Dr. David Alan Gilbert (git), 2019/05/14
- [Qemu-devel] [PULL 10/16] migration: update comments of migration bitmap, Dr. David Alan Gilbert (git), 2019/05/14
- [Qemu-devel] [PULL 11/16] migration/savevm: remove duplicate check of migration_is_blocked, Dr. David Alan Gilbert (git), 2019/05/14