src: introduce helper API for creating GSource for socket

We need to be able to create event loop watches using the
GSource API for sockets. GIOChannel is able todo this, but
we don't want to use the GIOChannel APIs for reading/writing,
and testing shows just using its GSource APIs is unreliable
on Windows.

This patch thus creates a standalone helper API for creating
a GSource for a socket file descriptor. This impl is derived
from code in QEMU's io/channel-watch.c file that was written
by myself & Paolo Bonzini & thus under Red Hat copyright.

Reviewed-by: Pavel Hrdina <phrdina@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

build-aux/syntax-check.mk

@@ -2339,3 +2339,6 @@ exclude_file_name_regexp--sc_prohibit_backslash_alignment = \
 
 exclude_file_name_regexp--sc_prohibit_always_true_header_tests = \
   ^src/util/(virfile|virnetdev|virnetdevip)\.[c,h]|$$
+
+exclude_file_name_regexp--sc_prohibit_select = \
+  ^build-aux/syntax-check\.mk|src/util/vireventglibwatch\.c$$

src/util/Makefile.inc.am

@@ -61,6 +61,8 @@ UTIL_SOURCES = \
 	util/virerrorpriv.h \
 	util/virevent.c \
 	util/virevent.h \
+	util/vireventglibwatch.c \
+	util/vireventglibwatch.h \
 	util/vireventpoll.c \
 	util/vireventpoll.h \
 	util/virfcp.c \

src/util/vireventglibwatch.c

@@ -0,0 +1,249 @@
+/*
+ * vireventglibwatch.c: GSource impl for sockets
+ *
+ * Copyright (C) 2015-2020 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 2.1 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 <config.h>
+
+#include "vireventglibwatch.h"
+
+#ifndef WIN32
+typedef struct virEventGLibFDSource virEventGLibFDSource;
+struct virEventGLibFDSource {
+    GSource parent;
+    GPollFD pollfd;
+    int fd;
+    GIOCondition condition;
+};
+
+
+static gboolean
+virEventGLibFDSourcePrepare(GSource *source G_GNUC_UNUSED,
+                            gint *timeout)
+{
+    *timeout = -1;
+
+    return FALSE;
+}
+
+
+static gboolean
+virEventGLibFDSourceCheck(GSource *source)
+{
+    virEventGLibFDSource *ssource = (virEventGLibFDSource *)source;
+
+    return ssource->pollfd.revents & ssource->condition;
+}
+
+
+static gboolean
+virEventGLibFDSourceDispatch(GSource *source,
+                             GSourceFunc callback,
+                             gpointer user_data)
+{
+    virEventGLibSocketFunc func = (virEventGLibSocketFunc)callback;
+    virEventGLibFDSource *ssource = (virEventGLibFDSource *)source;
+
+    return (*func)(ssource->fd,
+                   ssource->pollfd.revents & ssource->condition,
+                   user_data);
+}
+
+
+static void
+virEventGLibFDSourceFinalize(GSource *source G_GNUC_UNUSED)
+{
+}
+
+
+GSourceFuncs virEventGLibFDSourceFuncs = {
+    .prepare = virEventGLibFDSourcePrepare,
+    .check = virEventGLibFDSourceCheck,
+    .dispatch = virEventGLibFDSourceDispatch,
+    .finalize = virEventGLibFDSourceFinalize
+};
+
+
+GSource *virEventGLibCreateSocketWatch(int fd,
+                                       GIOCondition condition)
+{
+    GSource *source;
+    virEventGLibFDSource *ssource;
+
+    source = g_source_new(&virEventGLibFDSourceFuncs,
+                          sizeof(virEventGLibFDSource));
+    ssource = (virEventGLibFDSource *)source;
+
+    ssource->condition = condition;
+    ssource->fd = fd;
+
+    ssource->pollfd.fd = fd;
+    ssource->pollfd.events = condition;
+
+    g_source_add_poll(source, &ssource->pollfd);
+
+    return source;
+}
+
+#else /* WIN32 */
+
+# define WIN32_LEAN_AND_MEAN
+# include <winsock2.h>
+
+typedef struct virEventGLibSocketSource virEventGLibSocketSource;
+struct virEventGLibSocketSource {
+    GSource parent;
+    GPollFD pollfd;
+    int fd;
+    SOCKET socket;
+    HANDLE event;
+    int revents;
+    GIOCondition condition;
+};
+
+
+static gboolean
+virEventGLibSocketSourcePrepare(GSource *source G_GNUC_UNUSED,
+                                gint *timeout)
+{
+    *timeout = -1;
+
+    return FALSE;
+}
+
+
+/*
+ * NB, this impl only works when the socket is in non-blocking
+ * mode on Win32
+ */
+static gboolean
+virEventGLibSocketSourceCheck(GSource *source)
+{
+    static struct timeval tv0;
+
+    virEventGLibSocketSource *ssource = (virEventGLibSocketSource *)source;
+    WSANETWORKEVENTS ev;
+    fd_set rfds, wfds, xfds;
+
+    if (!ssource->condition)
+        return 0;
+
+    WSAEnumNetworkEvents(ssource->socket, ssource->event, &ev);
+
+    FD_ZERO(&rfds);
+    FD_ZERO(&wfds);
+    FD_ZERO(&xfds);
+    if (ssource->condition & G_IO_IN)
+        FD_SET(ssource->socket, &rfds);
+    if (ssource->condition & G_IO_OUT)
+        FD_SET(ssource->socket, &wfds);
+    if (ssource->condition & G_IO_PRI)
+        FD_SET(ssource->socket, &xfds);
+
+    ssource->revents = 0;
+    if (select(0, &rfds, &wfds, &xfds, &tv0) == 0)
+        return 0;
+
+    if (FD_ISSET(ssource->socket, &rfds))
+        ssource->revents |= G_IO_IN;
+
+    if (FD_ISSET(ssource->socket, &wfds))
+        ssource->revents |= G_IO_OUT;
+
+    if (FD_ISSET(ssource->socket, &xfds))
+        ssource->revents |= G_IO_PRI;
+
+    return ssource->revents;
+}
+
+
+static gboolean
+virEventGLibSocketSourceDispatch(GSource *source,
+                                 GSourceFunc callback,
+                                 gpointer user_data)
+{
+    virEventGLibSocketFunc func = (virEventGLibSocketFunc)callback;
+    virEventGLibSocketSource *ssource = (virEventGLibSocketSource *)source;
+
+    return (*func)(ssource->fd, ssource->revents, user_data);
+}
+
+
+static void
+virEventGLibSocketSourceFinalize(GSource *source)
+{
+    virEventGLibSocketSource *ssource = (virEventGLibSocketSource *)source;
+
+    WSAEventSelect(ssource->socket, NULL, 0);
+    CloseHandle(ssource->event);
+}
+
+
+GSourceFuncs virEventGLibSocketSourceFuncs = {
+    .prepare = virEventGLibSocketSourcePrepare,
+    .check = virEventGLibSocketSourceCheck,
+    .dispatch = virEventGLibSocketSourceDispatch,
+    .finalize = virEventGLibSocketSourceFinalize
+};
+
+
+GSource *virEventGLibCreateSocketWatch(int fd,
+                                       GIOCondition condition)
+{
+    GSource *source;
+    virEventGLibSocketSource *ssource;
+
+    source = g_source_new(&virEventGLibSocketSourceFuncs,
+                          sizeof(virEventGLibSocketSource));
+    ssource = (virEventGLibSocketSource *)source;
+
+    ssource->condition = condition;
+    ssource->fd = fd;
+    ssource->socket = _get_osfhandle(fd);
+    ssource->event = CreateEvent(NULL, FALSE, FALSE, NULL);
+    ssource->revents = 0;
+
+    ssource->pollfd.fd = (gintptr)ssource->event;
+    ssource->pollfd.events = G_IO_IN;
+
+    WSAEventSelect(ssource->socket, ssource->event,
+                   FD_READ | FD_ACCEPT | FD_CLOSE |
+                   FD_CONNECT | FD_WRITE | FD_OOB);
+
+    g_source_add_poll(source, &ssource->pollfd);
+
+    return source;
+}
+
+#endif /* WIN32 */
+
+
+guint virEventGLibAddSocketWatch(int fd,
+                                 GIOCondition condition,
+                                 GMainContext *context,
+                                 virEventGLibSocketFunc func,
+                                 gpointer opaque,
+                                 GDestroyNotify notify)
+{
+    g_autoptr(GSource) source = NULL;
+
+    source = virEventGLibCreateSocketWatch(fd, condition);
+    g_source_set_callback(source, (GSourceFunc)func, opaque, notify);
+
+    return g_source_attach(source, context);
+}

src/util/vireventglibwatch.h

@@ -0,0 +1,48 @@
+/*
+ * vireventglibwatch.h: GSource impl for sockets
+ *
+ * Copyright (C) 2015-2020 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 2.1 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/>.
+ */
+
+#pragma once
+
+#include "internal.h"
+
+/**
+ * virEventGLibCreateSocketWatch:
+ * @fd: the file descriptor
+ * @condition: the I/O condition
+ *
+ * Create a new main loop source that is able to
+ * monitor the file descriptor @fd for the
+ * I/O conditions in @condition.
+ *
+ * Returns: the new main loop source
+ */
+GSource *virEventGLibCreateSocketWatch(int fd,
+                                       GIOCondition condition);
+
+typedef gboolean (*virEventGLibSocketFunc)(int fd,
+                                           GIOCondition condition,
+                                           gpointer data);
+
+guint virEventGLibAddSocketWatch(int fd,
+                                 GIOCondition condition,
+                                 GMainContext *context,
+                                 virEventGLibSocketFunc func,
+                                 gpointer opaque,
+                                 GDestroyNotify notify);