io: introduce helper for creating channels from file descriptors

Depending on what object a file descriptor refers to a different
type of IO channel will be needed - either a QIOChannelFile or
a QIOChannelSocket. Introduce a qio_channel_new_fd() method
which will return the appropriate channel implementation.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

io/Makefile.objs

@@ -6,4 +6,5 @@ io-obj-y += channel-socket.o
 io-obj-y += channel-tls.o
 io-obj-y += channel-watch.o
 io-obj-y += channel-websock.o
+io-obj-y += channel-util.o
 io-obj-y += task.o

io/channel-util.c

@@ -0,0 +1,50 @@
+/*
+ * QEMU I/O channels utility APIs
+ *
+ * Copyright (c) 2016 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "io/channel-util.h"
+#include "io/channel-file.h"
+#include "io/channel-socket.h"
+
+
+static bool fd_is_socket(int fd)
+{
+    int optval;
+    socklen_t optlen;
+    optlen = sizeof(optval);
+    return qemu_getsockopt(fd,
+                           SOL_SOCKET,
+                           SO_TYPE,
+                           (char *)&optval,
+                           &optlen) == 0;
+}
+
+
+QIOChannel *qio_channel_new_fd(int fd,
+                               Error **errp)
+{
+    QIOChannel *ioc;
+
+    if (fd_is_socket(fd)) {
+        ioc = QIO_CHANNEL(qio_channel_socket_new_fd(fd, errp));
+    } else {
+        ioc = QIO_CHANNEL(qio_channel_file_new_fd(fd));
+    }
+    return ioc;
+}