sheepdog: move coroutine send/recv function to generic code

Outside coroutines, avoid busy waiting on EAGAIN by temporarily
making the socket blocking.

The API of qemu_recvv/qemu_sendv is slightly different from
do_readv/do_writev because they do not handle coroutines.  It
returns the number of bytes written before encountering an
EAGAIN.  The specificity of yielding on EAGAIN is entirely in
qemu-coroutine.c.

Reviewed-by: MORITA Kazutaka <morita.kazutaka@lab.ntt.co.jp>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qemu-coroutine-io.c

@@ -0,0 +1,96 @@
+/*
+ * Coroutine-aware I/O functions
+ *
+ * Copyright (C) 2009-2010 Nippon Telegraph and Telephone Corporation.
+ * Copyright (c) 2011, Red Hat, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+#include "qemu-common.h"
+#include "qemu_socket.h"
+#include "qemu-coroutine.h"
+
+int coroutine_fn qemu_co_recvv(int sockfd, struct iovec *iov,
+                               int len, int iov_offset)
+{
+    int total = 0;
+    int ret;
+    while (len) {
+        ret = qemu_recvv(sockfd, iov, len, iov_offset + total);
+        if (ret < 0) {
+            if (errno == EAGAIN) {
+                qemu_coroutine_yield();
+                continue;
+            }
+            if (total == 0) {
+                total = -1;
+            }
+            break;
+        }
+        if (ret == 0) {
+            break;
+        }
+        total += ret, len -= ret;
+    }
+
+    return total;
+}
+
+int coroutine_fn qemu_co_sendv(int sockfd, struct iovec *iov,
+                               int len, int iov_offset)
+{
+    int total = 0;
+    int ret;
+    while (len) {
+        ret = qemu_sendv(sockfd, iov, len, iov_offset + total);
+        if (ret < 0) {
+            if (errno == EAGAIN) {
+                qemu_coroutine_yield();
+                continue;
+            }
+            if (total == 0) {
+                total = -1;
+            }
+            break;
+        }
+        total += ret, len -= ret;
+    }
+
+    return total;
+}
+
+int coroutine_fn qemu_co_recv(int sockfd, void *buf, int len)
+{
+    struct iovec iov;
+
+    iov.iov_base = buf;
+    iov.iov_len = len;
+
+    return qemu_co_recvv(sockfd, &iov, len, 0);
+}
+
+int coroutine_fn qemu_co_send(int sockfd, void *buf, int len)
+{
+    struct iovec iov;
+
+    iov.iov_base = buf;
+    iov.iov_len = len;
+
+    return qemu_co_sendv(sockfd, &iov, len, 0);
+}