Postcopy; Handle userfault requests

userfaultfd is a Linux syscall that gives an fd that receives a stream
of notifications of accesses to pages registered with it and allows
the program to acknowledge those stalls and tell the accessing
thread to carry on.

We convert the requests from the kernel into messages back to the
source asking for the pages.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/migration/migration.h b/include/migration/migration.h
index a48471e026..329d5358d5 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -89,11 +89,14 @@ struct MigrationIncomingState {
      */
     QemuEvent main_thread_load_event;
 
+    bool           have_fault_thread;
     QemuThread     fault_thread;
     QemuSemaphore  fault_thread_sem;
 
     /* For the kernel to send us notifications */
     int       userfault_fd;
+    /* To tell the fault_thread to quit */
+    int       userfault_quit_fd;
     QEMUFile *to_src_file;
     QemuMutex rp_mutex;    /* We send replies from multiple threads */
     void     *postcopy_tmp_page;