[Qemu-devel] [PATCH FYI 07/46] io: add helper module for creating watches on FDs

["Daniel P. Berrange" <berrange@redhat.com>]

A number of the channel implementations will require the
ability to create watches on file descriptors / sockets.
To avoid duplicating this code in each channel, provide a
helper API for dealing with file descriptor watches.

There are two watch implementations provided. The first
is useful for bi-directional file descriptors such as
sockets, regular files, character devices, etc. The
second works with a pair of unidirectional file descriptors
such as pipes.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 include/io/channel-watch.h |  72 ++++++++++++++++
 io/Makefile.objs           |   1 +
 io/channel-watch.c         | 200 +++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 273 insertions(+)
 create mode 100644 include/io/channel-watch.h
 create mode 100644 io/channel-watch.c

diff --git a/include/io/channel-watch.h b/include/io/channel-watch.h
new file mode 100644
index 0000000..656358a
--- /dev/null
+++ b/include/io/channel-watch.h
@@ -0,0 +1,72 @@
+/*
+ * QEMU I/O channels watch helper APIs
+ *
+ * Copyright (c) 2015 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/>.
+ *
+ */
+
+#ifndef QIO_CHANNEL_WATCH_H__
+#define QIO_CHANNEL_WATCH_H__
+
+#include "io/channel.h"
+
+/*
+ * This module provides helper functions that will be needed by
+ * the various QIOChannel implementations, for creating watches
+ * on file descriptors / sockets
+ */
+
+/**
+ * qio_channel_create_fd_watch:
+ * @ioc: the channel object
+ * @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. This is able
+ * monitor block devices, character devices,
+ * sockets, pipes but not plain files.
+ *
+ * Returns: the new main loop source
+ */
+GSource *qio_channel_create_fd_watch(QIOChannel *ioc,
+                                     int fd,
+                                     GIOCondition condition);
+
+/**
+ * qio_channel_create_fd_pair_watch:
+ * @ioc: the channel object
+ * @fdread: the file descriptor for reading
+ * @fdwrite: the file descriptor for writing
+ * @condition: the I/O condition
+ *
+ * Create a new main loop source that is able to
+ * monitor the pair of file descriptors @fdread
+ * and @fdwrite for the I/O conditions in @condition.
+ * This is intended for monitoring unidirectional
+ * file descriptors such as pipes, where a pair
+ * of descriptors is required for bidirectional
+ * I/O
+ *
+ * Returns: the new main loop source
+ */
+GSource *qio_channel_create_fd_pair_watch(QIOChannel *ioc,
+                                          int fdread,
+                                          int fdwrite,
+                                          GIOCondition condition);
+
+#endif /* QIO_CHANNEL_WATCH_H__ */
diff --git a/io/Makefile.objs b/io/Makefile.objs
index a6ed361..b02ea90 100644
--- a/io/Makefile.objs
+++ b/io/Makefile.objs
@@ -1 +1,2 @@
 io-obj-y = channel.o
+io-obj-y += channel-watch.o
diff --git a/io/channel-watch.c b/io/channel-watch.c
new file mode 100644
index 0000000..9564605
--- /dev/null
+++ b/io/channel-watch.c
@@ -0,0 +1,200 @@
+/*
+ * QEMU I/O channels watch helper APIs
+ *
+ * Copyright (c) 2015 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-watch.h"
+
+typedef struct QIOChannelFDSource QIOChannelFDSource;
+struct QIOChannelFDSource {
+    GSource parent;
+    GPollFD fd;
+    QIOChannel *ioc;
+    GIOCondition condition;
+};
+
+
+typedef struct QIOChannelFDPairSource QIOChannelFDPairSource;
+struct QIOChannelFDPairSource {
+    GSource parent;
+    GPollFD fdread;
+    GPollFD fdwrite;
+    QIOChannel *ioc;
+    GIOCondition condition;
+};
+
+
+static gboolean
+qio_channel_fd_source_prepare(GSource *source G_GNUC_UNUSED,
+                              gint *timeout)
+{
+    *timeout = -1;
+
+    return FALSE;
+}
+
+
+static gboolean
+qio_channel_fd_source_check(GSource *source)
+{
+    QIOChannelFDSource *ssource = (QIOChannelFDSource *)source;
+
+    return ssource->fd.revents & ssource->condition;
+}
+
+
+static gboolean
+qio_channel_fd_source_dispatch(GSource *source,
+                               GSourceFunc callback,
+                               gpointer user_data)
+{
+    QIOChannelFunc func = (QIOChannelFunc)callback;
+    QIOChannelFDSource *ssource = (QIOChannelFDSource *)source;
+
+    return (*func)(ssource->ioc,
+                   ssource->fd.revents & ssource->condition,
+                   user_data);
+}
+
+
+static void
+qio_channel_fd_source_finalize(GSource *source)
+{
+    QIOChannelFDSource *ssource = (QIOChannelFDSource *)source;
+
+    object_unref(OBJECT(ssource->ioc));
+}
+
+
+static gboolean
+qio_channel_fd_pair_source_prepare(GSource *source G_GNUC_UNUSED,
+                                   gint *timeout)
+{
+    *timeout = -1;
+
+    return FALSE;
+}
+
+
+static gboolean
+qio_channel_fd_pair_source_check(GSource *source)
+{
+    QIOChannelFDPairSource *ssource = (QIOChannelFDPairSource *)source;
+    GIOCondition poll_condition = ssource->fdread.revents |
+        ssource->fdwrite.revents;
+
+    return poll_condition & ssource->condition;
+}
+
+
+static gboolean
+qio_channel_fd_pair_source_dispatch(GSource *source,
+                                    GSourceFunc callback,
+                                    gpointer user_data)
+{
+    QIOChannelFunc func = (QIOChannelFunc)callback;
+    QIOChannelFDPairSource *ssource = (QIOChannelFDPairSource *)source;
+    GIOCondition poll_condition = ssource->fdread.revents |
+        ssource->fdwrite.revents;
+
+    return (*func)(ssource->ioc,
+                   poll_condition & ssource->condition,
+                   user_data);
+}
+
+
+static void
+qio_channel_fd_pair_source_finalize(GSource *source)
+{
+    QIOChannelFDPairSource *ssource = (QIOChannelFDPairSource *)source;
+
+    object_unref(OBJECT(ssource->ioc));
+}
+
+
+GSourceFuncs qio_channel_fd_source_funcs = {
+    qio_channel_fd_source_prepare,
+    qio_channel_fd_source_check,
+    qio_channel_fd_source_dispatch,
+    qio_channel_fd_source_finalize
+};
+
+
+GSourceFuncs qio_channel_fd_pair_source_funcs = {
+    qio_channel_fd_pair_source_prepare,
+    qio_channel_fd_pair_source_check,
+    qio_channel_fd_pair_source_dispatch,
+    qio_channel_fd_pair_source_finalize
+};
+
+
+GSource *qio_channel_create_fd_watch(QIOChannel *ioc,
+                                     int fd,
+                                     GIOCondition condition)
+{
+    GSource *source;
+    QIOChannelFDSource *ssource;
+
+    source = g_source_new(&qio_channel_fd_source_funcs,
+                          sizeof(QIOChannelFDSource));
+    g_source_set_name(source, "QIOChannelFD");
+    ssource = (QIOChannelFDSource *)source;
+
+    ssource->ioc = ioc;
+    object_ref(OBJECT(ioc));
+
+    ssource->condition = condition;
+
+    ssource->fd.fd = fd;
+    ssource->fd.events = condition;
+
+    g_source_add_poll(source, &ssource->fd);
+
+    return source;
+}
+
+
+GSource *qio_channel_create_fd_pair_watch(QIOChannel *ioc,
+                                          int fdread,
+                                          int fdwrite,
+                                          GIOCondition condition)
+{
+    GSource *source;
+    QIOChannelFDPairSource *ssource;
+
+    source = g_source_new(&qio_channel_fd_pair_source_funcs,
+                          sizeof(QIOChannelFDPairSource));
+    g_source_set_name(source, "QIOChannelFDPair");
+    ssource = (QIOChannelFDPairSource *)source;
+
+    ssource->ioc = ioc;
+    object_ref(OBJECT(ioc));
+
+    ssource->condition = condition;
+
+    ssource->fdread.fd = fdread;
+    ssource->fdread.events = condition & G_IO_IN;
+
+    ssource->fdwrite.fd = fdwrite;
+    ssource->fdwrite.events = condition & G_IO_OUT;
+
+    g_source_add_poll(source, &ssource->fdread);
+    g_source_add_poll(source, &ssource->fdwrite);
+
+    return source;
+}
-- 
2.4.3