sheepdog: restart I/O when socket becomes ready in do_co_req()

Currently, no one reenters the yielded coroutine.  This fixes it.
Signed-off-by: NMORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/sheepdog.c

@@ -577,10 +577,21 @@ out:
     return ret;
 }
 
+static void restart_co_req(void *opaque)
+{
+    Coroutine *co = opaque;
+
+    qemu_coroutine_enter(co, NULL);
+}
+
 static coroutine_fn int do_co_req(int sockfd, SheepdogReq *hdr, void *data,
                                   unsigned int *wlen, unsigned int *rlen)
 {
     int ret;
+    Coroutine *co;
+
+    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);
@@ -588,6 +599,8 @@ static coroutine_fn int do_co_req(int sockfd, SheepdogReq *hdr, void *data,
         goto out;
     }
 
+    qemu_aio_set_fd_handler(sockfd, restart_co_req, NULL, NULL, co);
+
     ret = qemu_co_recv(sockfd, hdr, sizeof(*hdr));
     if (ret < sizeof(*hdr)) {
         error_report("failed to get a rsp, %s", strerror(errno));
@@ -609,6 +622,7 @@ static coroutine_fn int do_co_req(int sockfd, SheepdogReq *hdr, void *data,
     }
     ret = 0;
 out:
+    qemu_aio_set_fd_handler(sockfd, NULL, NULL, NULL, NULL);
     socket_set_nonblock(sockfd);
     return ret;
 }