qemu-kvm/kvm-QIOChannelSocket-Introduce-assert-and-reduce-ifdefs-.patch

From cbfaf86331c2b2e01a2083303b7554672bf991b7 Mon Sep 17 00:00:00 2001
From: Leonardo Bras <leobras@redhat.com>
Date: Mon, 20 Jun 2022 02:39:42 -0300
Subject: [PATCH 24/37] QIOChannelSocket: Introduce assert and reduce ifdefs to
 improve readability
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RH-Author: Leonardo Brás <leobras@redhat.com>
RH-MergeRequest: 191: MSG_ZEROCOPY + Multifd @ rhel8.7
RH-Commit: [24/26] b50e2e65307149f247155a7f7a032dc99e57718d
RH-Bugzilla: 2072049
RH-Acked-by: Peter Xu <peterx@redhat.com>
RH-Acked-by: Daniel P. Berrangé <berrange@redhat.com>
RH-Acked-by: Dr. David Alan Gilbert <dgilbert@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>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
  dgilbert: Fixed up thinko'd g_assert_unreachable->g_assert_not_reached
(cherry picked from commit 803ca43e4c7fcf32f9f68c118301ccd0c83ece3f)
Signed-off-by: Leonardo Bras <leobras@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 38a46ba213..7d37b39de7 100644
--- a/io/channel-socket.c
+++ b/io/channel-socket.c
@@ -579,11 +579,17 @@ 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_not_reached();
 #endif
+    }
 
  retry:
     ret = sendmsg(sioc->fd, &msg, sflags);
@@ -593,15 +599,13 @@ 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,
-- 
2.35.3