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migration: Add save_postcopy_prepare() savevm handler

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Add a savevm handler for a module to opt-in sending extra sections right
before postcopy starts, and before VM is stopped.

RAM will start to use this new savevm handler in the next patch to do flush
and sync for multifd pages.

Note that we choose to do it before VM stopped because the current only
potential user is not sensitive to VM status, so doing it before VM is
stopped is preferred to enlarge any postcopy downtime.

It is still a bit unfortunate that we need to introduce such a new savevm
handler just for the only use case, however it's so far the cleanest.

Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Prasad Pandit <pjp@fedoraproject.org>
Reviewed-by: Fabiano Rosas <farosas@suse.de>
Message-ID: <20250411114534.3370816-4-ppandit@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
This commit is contained in:
Peter Xu 2025-04-11 17:15:30 +05:30
parent 00f3fcef19
commit 1d48111601
4 changed files with 53 additions and 0 deletions
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33
migration/savevm.c
View file

@ -1523,6 +1523,39 @@ void qemu_savevm_state_complete_postcopy(QEMUFile *f)
qemu_fflush(f);
}
bool qemu_savevm_state_postcopy_prepare(QEMUFile *f, Error **errp)
{
SaveStateEntry *se;
bool ret;
QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
if (!se->ops || !se->ops->save_postcopy_prepare) {
continue;
}
if (se->ops->is_active) {
if (!se->ops->is_active(se->opaque)) {
continue;
}
}
trace_savevm_section_start(se->idstr, se->section_id);
save_section_header(f, se, QEMU_VM_SECTION_PART);
ret = se->ops->save_postcopy_prepare(f, se->opaque, errp);
save_section_footer(f, se);
trace_savevm_section_end(se->idstr, se->section_id, ret);
if (!ret) {
assert(*errp);
return false;
}
}
return true;
}
int qemu_savevm_state_complete_precopy_iterable(QEMUFile *f, bool in_postcopy)
{
int64_t start_ts_each, end_ts_each;