migration: Add postcopy_thread_create()

Postcopy create threads. A common manner is we init a sem and use it to sync
with the thread.  Namely, we have fault_thread_sem and listen_thread_sem and
they're only used for this.

Make it a shared infrastructure so it's easier to create yet another thread.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Message-Id: <20220301083925.33483-7-peterx@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

1 files changed, 5 insertions, 3 deletions

diff --git a/migration/migration.h b/migration/migration.h
index 42c7395094..8445e1d14a 100644
--- a/migration/migration.h
+++ b/migration/migration.h
@@ -70,7 +70,11 @@ struct MigrationIncomingState {
     /* A hook to allow cleanup at the end of incoming migration */
     void *transport_data;
     void (*transport_cleanup)(void *data);
-
+    /*
+     * Used to sync thread creations.  Note that we can't create threads in
+     * parallel with this sem.
+     */
+    QemuSemaphore  thread_sync_sem;
     /*
      * Free at the start of the main state load, set as the main thread finishes
      * loading state.
@@ -83,13 +87,11 @@ struct MigrationIncomingState {
     size_t         largest_page_size;
     bool           have_fault_thread;
     QemuThread     fault_thread;
-    QemuSemaphore  fault_thread_sem;
     /* Set this when we want the fault thread to quit */
     bool           fault_thread_quit;
 
     bool           have_listen_thread;
     QemuThread     listen_thread;
-    QemuSemaphore  listen_thread_sem;
 
     /* For the kernel to send us notifications */
     int       userfault_fd;