On 6/3/2021 3:36 PM, Dr. David Alan Gilbert wrote:
> * Steven Sistare (steven.sist...@oracle.com) wrote:
>> On 5/24/2021 6:39 AM, Dr. David Alan Gilbert wrote:
>>> * Steven Sistare (steven.sist...@oracle.com) wrote:
>>>> On 5/20/2021 9:13 AM, Dr. David Alan Gilbert wrote:
>>>>> On the 'restart' branch of questions; can you explain,
>>>>> other than the passing of the fd's, why the outgoing side of
>>>>> qemu's 'migrate exec:' doesn't work for you?
>>>>
>>>> I'm not sure what I should describe. Can you be more specific?
>>>> Do you mean: can we add the cpr specific bits to the migrate exec code?
>>>
>>> Yes; if possible I'd prefer to just keep the one exec mechanism.
>>> It has an advantage of letting you specify the new command line; that
>>> avoids the problems I'd pointed out with needing to change the command
>>> line if a hotplug had happened. It also means we only need one chunk of
>>> exec code.
>>
>> [...]
>
> I'm not quite sure what I want in the incoming there, but that is
> already the source execing the destination qemu - although I think we'd
> probably need to check if that's actually via an intermediary.
>
>> We could shoehorn cpr restart into the migrate exec path by defining a new
>> migration
>> capability that the client would set before issuing the migrate command.
>> However, the
>> implementation code would be sprinkled with conditionals to suppress
>> migrate-only bits
>> and call cpr-only bits. IMO that would be less maintainable than having a
>> separate
>> cprsave function. Currently cprsave does not duplicate any migration
>> functionality.
>> cprsave calls qemu_save_device_state() which is used by xen.
>
> To me it feels like cprsave in particular is replicating more code.
In the attached file I annotated lines of code that have some overlap
with migration code actions. They include vm control, global_state_store,
and vmstate save, and cover 18 lines of 78 total. I did not include the
body of qf_file_open because it is also called by xen.
The migration code adds capabilities, parameters, state, status, info,
precopy, postcopy, dirty bitmap, events, notifiers, 6 channel types,
blockers, pause+resume, return path, request-reply commands, throttling, colo,
blocks, phases, iteration, and threading, implemented by 20000+ lines of code.
To me it seems wrong to throw cpr into that mix to avoid adding tens of lines
of similar code.
- Steve
void cprsave(const char *file, CprMode mode, Error **errp)
{
int ret = 0;
** QEMUFile *f;
** int saved_vm_running = runstate_is_running();
bool restart = (mode == CPR_MODE_RESTART);
bool reboot = (mode == CPR_MODE_REBOOT);
if (reboot && qemu_ram_volatile(errp)) {
return;
}
if (restart && xen_enabled()) {
error_setg(errp, "xen does not support cprsave restart");
return;
}
if (migrate_colo_enabled()) {
error_setg(errp, "error: cprsave does not support x-colo");
return;
}
if (replay_mode != REPLAY_MODE_NONE) {
error_setg(errp, "error: cprsave does not support replay");
return;
}
f = qf_file_open(file, O_CREAT | O_WRONLY | O_TRUNC, 0600, "cprsave",
errp);
if (!f) {
return;
}
** ret = global_state_store();
** if (ret) {
** error_setg(errp, "Error saving global state");
** qemu_fclose(f);
** return;
** }
if (runstate_check(RUN_STATE_SUSPENDED)) {
/* Update timers_state before saving. Suspend did not so do. */
cpu_disable_ticks();
}
** vm_stop(RUN_STATE_SAVE_VM);
cpr_is_active = true;
** ret = qemu_save_device_state(f);
** qemu_fclose(f);
** if (ret < 0) {
** error_setg(errp, "Error %d while saving VM state", ret);
** goto err;
** }
if (reboot) {
shutdown_action = SHUTDOWN_ACTION_POWEROFF;
qemu_system_shutdown_request(SHUTDOWN_CAUSE_GUEST_SHUTDOWN);
} else if (restart) {
if (!qemu_chr_cpr_capable(errp)) {
goto err;
}
if (vfio_cprsave(errp)) {
goto err;
}
walkenv(FD_PREFIX, preserve_fd, 0);
vhost_dev_reset_all();
qemu_term_exit();
setenv("QEMU_START_FREEZE", "", 1);
qemu_system_exec_request();
}
goto done;
err:
** if (saved_vm_running) {
** vm_start();
** }
done:
cpr_is_active = false;
return;
}
