vl: allow other threads to do qemu_system_vmstop_request

There patch protects vmstop_requested with a lock and introduces
qemu_system_vmstop_request_prepare.

Together with the new call to qemu_vmstop_requested in vm_start,
qemu_system_vmstop_request_prepare avoids a race where the VM could remain
stopped even though the iostatus of a block device has already been set
(for example).

qemu_system_vmstop_request_prepare however also lets the caller thread
delay observation of the state change until it has itself communicated
that change to the user.  This delay avoids any possibility of a wrong
reordering of the BLOCK_IO_ERROR event and the subsequent STOP event.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/include/sysemu/sysemu.h b/include/sysemu/sysemu.h
index 277230db49..6b4cc133c5 100644
--- a/include/sysemu/sysemu.h
+++ b/include/sysemu/sysemu.h
@@ -62,6 +62,7 @@ void qemu_system_powerdown_request(void);
 void qemu_register_powerdown_notifier(Notifier *notifier);
 void qemu_system_debug_request(void);
 void qemu_system_vmstop_request(RunState reason);
+void qemu_system_vmstop_request_prepare(void);
 int qemu_shutdown_requested_get(void);
 int qemu_reset_requested_get(void);
 void qemu_system_killed(int signal, pid_t pid);