migration: use QEMUFile for migration channel lifetime

As a start, use QEMUFile to store the destination and close it.
qemu_get_fd gets a file descriptor that will be used by the write
callbacks.

Reviewed-by: Orit Wasserman <owasserm@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
diff --git a/migration-unix.c b/migration-unix.c
index 4693b43..11917f4 100644
--- a/migration-unix.c
+++ b/migration-unix.c
@@ -39,28 +39,17 @@
     return write(s->fd, buf, size);
 }
 
-static int unix_close(MigrationState *s)
-{
-    int r = 0;
-    DPRINTF("unix_close\n");
-    if (close(s->fd) < 0) {
-        r = -errno;
-    }
-    return r;
-}
-
 static void unix_wait_for_connect(int fd, void *opaque)
 {
     MigrationState *s = opaque;
 
     if (fd < 0) {
         DPRINTF("migrate connect error\n");
-        s->fd = -1;
+        s->migration_file = NULL;
         migrate_fd_error(s);
     } else {
         DPRINTF("migrate connect success\n");
-        s->fd = fd;
-        socket_set_block(s->fd);
+        s->migration_file = qemu_fopen_socket(fd, "wb");
         migrate_fd_connect(s);
     }
 }
@@ -69,9 +58,7 @@
 {
     s->get_error = unix_errno;
     s->write = unix_write;
-    s->close = unix_close;
-
-    s->fd = unix_nonblocking_connect(path, unix_wait_for_connect, s, errp);
+    unix_nonblocking_connect(path, unix_wait_for_connect, s, errp);
 }
 
 static void unix_accept_incoming_migration(void *opaque)