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: NMORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>

block/sheepdog.c

@@ -468,6 +468,8 @@ static int connect_to_sdog(BDRVSheepdogState *s)
     if (err != NULL) {
         qerror_report_err(err);
         error_free(err);
+    } else {
+        socket_set_nonblock(fd);
     }
 
     return fd;
@@ -523,7 +525,6 @@ static coroutine_fn void do_co_req(void *opaque)
     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 @@ static coroutine_fn void do_co_req(void *opaque)
     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 @@ static int get_sheep_fd(BDRVSheepdogState *s)
         return fd;
     }
 
-    socket_set_nonblock(fd);
-
     qemu_aio_set_fd_handler(fd, co_read_response, NULL, aio_flush_request, s);
     return fd;
 }