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migration: Add MIG_CMD_SWITCHOVER_START and its load handler

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This QEMU_VM_COMMAND sub-command and its switchover_start SaveVMHandler is
used to mark the switchover point in main migration stream.

It can be used to inform the destination that all pre-switchover main
migration stream data has been sent/received so it can start to process
post-switchover data that it might have received via other migration
channels like the multifd ones.

Add also the relevant MigrationState bit stream compatibility property and
its hw_compat entry.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Reviewed-by: Zhang Chen <zhangckid@gmail.com> # for the COLO part
Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@oracle.com>
Link: https://lore.kernel.org/qemu-devel/311be6da85fc7e49a7598684d80aa631778dcbce.1741124640.git.maciej.szmigiero@oracle.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>
This commit is contained in:
Maciej S. Szmigiero 2025-03-04 23:03:32 +01:00 • committed by Cédric Le Goater
parent b5aa74968b
commit 4e55cb3cde
12 changed files with 87 additions and 0 deletions
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39
migration/savevm.c
View file

@ -90,6 +90,7 @@ enum qemu_vm_cmd {
MIG_CMD_ENABLE_COLO, /* Enable COLO */
MIG_CMD_POSTCOPY_RESUME, /* resume postcopy on dest */
MIG_CMD_RECV_BITMAP, /* Request for recved bitmap on dst */
MIG_CMD_SWITCHOVER_START, /* Switchover start notification */
MIG_CMD_MAX
};
@ -109,6 +110,7 @@ static struct mig_cmd_args {
[MIG_CMD_POSTCOPY_RESUME] = { .len = 0, .name = "POSTCOPY_RESUME" },
[MIG_CMD_PACKAGED] = { .len = 4, .name = "PACKAGED" },
[MIG_CMD_RECV_BITMAP] = { .len = -1, .name = "RECV_BITMAP" },
[MIG_CMD_SWITCHOVER_START] = { .len = 0, .name = "SWITCHOVER_START" },
[MIG_CMD_MAX] = { .len = -1, .name = "MAX" },
};
@ -1201,6 +1203,19 @@ void qemu_savevm_send_recv_bitmap(QEMUFile *f, char *block_name)
qemu_savevm_command_send(f, MIG_CMD_RECV_BITMAP, len + 1, (uint8_t *)buf);
}
static void qemu_savevm_send_switchover_start(QEMUFile *f)
{
trace_savevm_send_switchover_start();
qemu_savevm_command_send(f, MIG_CMD_SWITCHOVER_START, 0, NULL);
}
void qemu_savevm_maybe_send_switchover_start(QEMUFile *f)
{
if (migrate_send_switchover_start()) {
qemu_savevm_send_switchover_start(f);
}
}
bool qemu_savevm_state_blocked(Error **errp)
{
SaveStateEntry *se;
@ -1687,6 +1702,7 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
ret = qemu_file_get_error(f);
if (ret == 0) {
qemu_savevm_maybe_send_switchover_start(f);
qemu_savevm_state_complete_precopy(f, false);
ret = qemu_file_get_error(f);
}
@ -2383,6 +2399,26 @@ static int loadvm_process_enable_colo(MigrationIncomingState *mis)
return ret;
}
static int loadvm_postcopy_handle_switchover_start(void)
{
SaveStateEntry *se;
QTAILQ_FOREACH(se, &savevm_state.handlers, entry) {
int ret;
if (!se->ops || !se->ops->switchover_start) {
continue;
}
ret = se->ops->switchover_start(se->opaque);
if (ret < 0) {
return ret;
}
}
return 0;
}
/*
* Process an incoming 'QEMU_VM_COMMAND'
* 0 just a normal return
@ -2481,6 +2517,9 @@ static int loadvm_process_command(QEMUFile *f)
case MIG_CMD_ENABLE_COLO:
return loadvm_process_enable_colo(mis);
case MIG_CMD_SWITCHOVER_START:
return loadvm_postcopy_handle_switchover_start();
}
return 0;