domain never exits after using 'xl save'

[James Dingwall <james-xen@xxxxxxxxxxxxxx>]

Hi,

This is an issue that was observed on 4.11.3 but I have reproduced on 4.14.3.
After using the `xl save` command the associated `xl create` process exits
which later results in the domain not being cleaned up when the guest is
shutdown.

e.g.:

# xl list -v | grep d13cc54d-dcb8-4337-9dfe-3b04f671b16
guest01  15  2048     3     -b----    1555.9 
d13cc54d-dcb8-4337-9dfe-3b04f671b16a        - system_u:system_r:migrate_domU_t

# ps -ef | grep d13cc54d-dcb8-4337-9dfe-3b04f671b16
root     18694     1  0 Sep22 ?        00:00:00 /usr/sbin/xl create -p 
/etc/xen/config/d13cc54d-dcb8-4337-9dfe-3b04f671b16a.cfg

# xl save -p guest01 /vmsave/guest01.mem
Saving to /vmsave/guest01.mem new xl format (info 0x3/0x0/2900)
xc: info: Saving domain 15, type x86 HVM
xc: Frames: 1044480/1044480  100%
xc: End of stream: 0/0    0%

# xl list -v | grep d13cc54d-dcb8-4337-9dfe-3b04f671b16
guest01  15  2048     3     --p---    1558.3 
d13cc54d-dcb8-4337-9dfe-3b04f671b16a        - system_u:system_r:migrate_domU_t

# ps -ef | grep d13cc54d-dcb8-4337-9dfe-3b04f671b16
- no matches -

# xl unpause guest01

# xl list -v | grep d13cc54d-dcb8-4337-9dfe-3b04f671b16
guest01  15  2048     3     -b----    1559.0 
d13cc54d-dcb8-4337-9dfe-3b04f671b16a        - system_u:system_r:migrate_domU_t

# xl shutdown guest01

# xl list -v | grep d13cc54d-dcb8-4337-9dfe-3b04f671b16
guest01  15  2048     3     ---s--    1575.8 
d13cc54d-dcb8-4337-9dfe-3b04f671b16a        0 system_u:system_r:migrate_domU_t


What we would expect is that the `xl create` process remains running so that
when the domain is later shutdown then it gets cleaned up without having to
manually `xl destroy`.

tools/xl/xl_vmcontrol.c handle_domain_death() has (0 == DOMAIN_RESTART_NONE in 
xl.h)

    case LIBXL_SHUTDOWN_REASON_SUSPEND:
        LOG("Domain has suspended.");
        return 0;

The while(1) loop of create_domain() has a switch statement which handles this
return value with:

            case DOMAIN_RESTART_NONE:
                LOG("Done. Exiting now");
                libxl_event_free(ctx, event);
                ret = 0;
                goto out;


Is this the expected behaviour?  Would an approach to getting the behaviour we
want be to change the return value from handle_domain_death() to one which
doesn't trigger the exit?

Thanks,
James