sheepdog: use non-blocking fd in coroutine context

Using a blocking socket in the coroutine context reduces the chance of
switching to other work.  This patch makes the sheepdog driver use a
non-blocking fd always.

Signed-off-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/block/sheepdog.c b/block/sheepdog.c
index c711c28..27abef2 100644
--- a/block/sheepdog.c
+++ b/block/sheepdog.c
@@ -468,6 +468,8 @@
     if (err != NULL) {
         qerror_report_err(err);
         error_free(err);
+    } else {
+        socket_set_nonblock(fd);
     }
 
     return fd;
@@ -523,7 +525,6 @@
     co = qemu_coroutine_self();
     qemu_aio_set_fd_handler(sockfd, NULL, restart_co_req, NULL, co);
 
-    socket_set_block(sockfd);
     ret = send_co_req(sockfd, hdr, data, wlen);
     if (ret < 0) {
         goto out;
@@ -553,7 +554,6 @@
     ret = 0;
 out:
     qemu_aio_set_fd_handler(sockfd, NULL, NULL, NULL, NULL);
-    socket_set_nonblock(sockfd);
 
     srco->ret = ret;
     srco->finished = true;
@@ -776,8 +776,6 @@
         return fd;
     }
 
-    socket_set_nonblock(fd);
-
     qemu_aio_set_fd_handler(fd, co_read_response, NULL, aio_flush_request, s);
     return fd;
 }