The only realization, which may have incoming fds is
qio_channel_socket_readv() (in io/channel-socket.c).
qio_channel_socket_readv() do call (through
qio_channel_socket_copy_fds()) qemu_socket_set_block() and
qemu_set_cloexec() for each fd.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@yandex-team.ru>
---
 include/io/channel.h | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/include/io/channel.h b/include/io/channel.h
index 234e5db70d..b848d50b99 100644
--- a/include/io/channel.h
+++ b/include/io/channel.h
@@ -117,6 +117,12 @@ struct QIOChannelClass {
                          size_t nfds,
                          int flags,
                          Error **errp);
+
+    /*
+     * The io_readv handler must guarantee that all
+     * incoming fds are set BLOCKING and CLOEXEC (if
+     * available).
+     */
     ssize_t (*io_readv)(QIOChannel *ioc,
                         const struct iovec *iov,
                         size_t niov,
@@ -124,6 +130,7 @@ struct QIOChannelClass {
                         size_t *nfds,
                         int flags,
                         Error **errp);
+
     int (*io_close)(QIOChannel *ioc,
                     Error **errp);
     GSource * (*io_create_watch)(QIOChannel *ioc,
@@ -234,6 +241,9 @@ void qio_channel_set_name(QIOChannel *ioc,
  * was allocated. It is the callers responsibility
  * to call close() on each file descriptor and to
  * call g_free() on the array pointer in @fds.
+ * qio_channel_readv_full() guarantees that all
+ * incoming fds are set BLOCKING and CLOEXEC (if
+ * available).
  *
  * It is an error to pass a non-NULL @fds parameter
  * unless qio_channel_has_feature() returns a true
-- 
2.48.1