[PATCH v4 1/4] QIOChannelSocket: Introduce assert and reduce ifdefs to improve readability

[Leonardo Bras <leobras@redhat.com>]

During implementation of MSG_ZEROCOPY feature, a lot of #ifdefs were
introduced, particularly at qio_channel_socket_writev().

Rewrite some of those changes so it's easier to read.

Also, introduce an assert to help detect incorrect zero-copy usage is when
it's disabled on build.

Signed-off-by: Leonardo Bras <leobras@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
---
 io/channel-socket.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/io/channel-socket.c b/io/channel-socket.c
index dc9c165de1..dac9e60c20 100644
--- a/io/channel-socket.c
+++ b/io/channel-socket.c
@@ -578,11 +578,17 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc,
         memcpy(CMSG_DATA(cmsg), fds, fdsize);
     }
 
-#ifdef QEMU_MSG_ZEROCOPY
     if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) {
+#ifdef QEMU_MSG_ZEROCOPY
         sflags = MSG_ZEROCOPY;
-    }
+#else
+        /*
+         * We expect QIOChannel class entry point to have
+         * blocked this code path already
+         */
+        g_assert_unreachable();
 #endif
+    }
 
  retry:
     ret = sendmsg(sioc->fd, &msg, sflags);
@@ -592,15 +598,13 @@ static ssize_t qio_channel_socket_writev(QIOChannel *ioc,
             return QIO_CHANNEL_ERR_BLOCK;
         case EINTR:
             goto retry;
-#ifdef QEMU_MSG_ZEROCOPY
         case ENOBUFS:
-            if (sflags & MSG_ZEROCOPY) {
+            if (flags & QIO_CHANNEL_WRITE_FLAG_ZERO_COPY) {
                 error_setg_errno(errp, errno,
                                  "Process can't lock enough memory for using MSG_ZEROCOPY");
                 return -1;
             }
             break;
-#endif
         }
 
         error_setg_errno(errp, errno,
-- 
2.36.1