io: add abstract QIOChannel classes

Start the new generic I/O channel framework by defining a
QIOChannel abstract base class. This is designed to feel
similar to GLib's GIOChannel, but with the addition of
support for using iovecs, qemu error reporting, file
descriptor passing, coroutine integration and use of
the QOM framework for easier sub-classing.

The intention is that anywhere in QEMU that almost
anywhere that deals with sockets will use this new I/O
infrastructure, so that it becomes trivial to then layer
in support for TLS encryption. This will at least include
the VNC server, char device backend and migration code.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

MAINTAINERS

@@ -1243,6 +1243,13 @@ S: Odd fixes
 F: util/buffer.c
 F: include/qemu/buffer.h
 
+I/O Channels
+M: Daniel P. Berrange <berrange@redhat.com>
+S: Maintained
+F: io/
+F: include/io/
+F: tests/test-io-*
+
 Usermode Emulation
 ------------------
 Overall

Makefile

@@ -159,6 +159,7 @@ dummy := $(call unnest-vars,, \
                 crypto-obj-y \
                 crypto-aes-obj-y \
                 qom-obj-y \
+                io-obj-y \
                 common-obj-y \
                 common-obj-m)
 
@@ -178,6 +179,7 @@ SOFTMMU_SUBDIR_RULES=$(filter %-softmmu,$(SUBDIR_RULES))
 
 $(SOFTMMU_SUBDIR_RULES): $(block-obj-y)
 $(SOFTMMU_SUBDIR_RULES): $(crypto-obj-y)
+$(SOFTMMU_SUBDIR_RULES): $(io-obj-y)
 $(SOFTMMU_SUBDIR_RULES): config-all-devices.mak
 
 subdir-%:

Makefile.objs

@@ -28,6 +28,11 @@ crypto-aes-obj-y = crypto/
 
 qom-obj-y = qom/
 
+#######################################################################
+# io-obj-y is code used by both qemu system emulation and qemu-img
+
+io-obj-y = io/
+
 ######################################################################
 # Target independent part of system emulation. The long term path is to
 # suppress *all* target specific code in case of system emulation, i.e. a

Makefile.target

@@ -176,6 +176,7 @@ dummy := $(call unnest-vars,.., \
                crypto-obj-y \
                crypto-aes-obj-y \
                qom-obj-y \
+               io-obj-y \
                common-obj-y \
                common-obj-m)
 target-obj-y := $(target-obj-y-save)
@@ -185,6 +186,7 @@ all-obj-y += $(qom-obj-y)
 all-obj-$(CONFIG_SOFTMMU) += $(block-obj-y)
 all-obj-$(CONFIG_USER_ONLY) += $(crypto-aes-obj-y)
 all-obj-$(CONFIG_SOFTMMU) += $(crypto-obj-y)
+all-obj-$(CONFIG_SOFTMMU) += $(io-obj-y)
 
 $(QEMU_PROG_BUILD): config-devices.mak
 

include/io/channel.h

@@ -0,0 +1,502 @@
+/*
+ * QEMU I/O channels
+ *
+ * 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_H__
+#define QIO_CHANNEL_H__
+
+#include "qemu-common.h"
+#include "qapi/error.h"
+#include "qom/object.h"
+
+#define TYPE_QIO_CHANNEL "qio-channel"
+#define QIO_CHANNEL(obj)                                    \
+    OBJECT_CHECK(QIOChannel, (obj), TYPE_QIO_CHANNEL)
+#define QIO_CHANNEL_CLASS(klass)                                    \
+    OBJECT_CLASS_CHECK(QIOChannelClass, klass, TYPE_QIO_CHANNEL)
+#define QIO_CHANNEL_GET_CLASS(obj)                                  \
+    OBJECT_GET_CLASS(QIOChannelClass, obj, TYPE_QIO_CHANNEL)
+
+typedef struct QIOChannel QIOChannel;
+typedef struct QIOChannelClass QIOChannelClass;
+
+#define QIO_CHANNEL_ERR_BLOCK -2
+
+typedef enum QIOChannelFeature QIOChannelFeature;
+
+enum QIOChannelFeature {
+    QIO_CHANNEL_FEATURE_FD_PASS  = (1 << 0),
+    QIO_CHANNEL_FEATURE_SHUTDOWN = (1 << 1),
+};
+
+
+typedef enum QIOChannelShutdown QIOChannelShutdown;
+
+enum QIOChannelShutdown {
+    QIO_CHANNEL_SHUTDOWN_BOTH,
+    QIO_CHANNEL_SHUTDOWN_READ,
+    QIO_CHANNEL_SHUTDOWN_WRITE,
+};
+
+typedef gboolean (*QIOChannelFunc)(QIOChannel *ioc,
+                                   GIOCondition condition,
+                                   gpointer data);
+
+/**
+ * QIOChannel:
+ *
+ * The QIOChannel defines the core API for a generic I/O channel
+ * class hierarchy. It is inspired by GIOChannel, but has the
+ * following differences
+ *
+ *  - Use QOM to properly support arbitrary subclassing
+ *  - Support use of iovecs for efficient I/O with multiple blocks
+ *  - None of the character set translation, binary data exclusively
+ *  - Direct support for QEMU Error object reporting
+ *  - File descriptor passing
+ *
+ * This base class is abstract so cannot be instantiated. There
+ * will be subclasses for dealing with sockets, files, and higher
+ * level protocols such as TLS, WebSocket, etc.
+ */
+
+struct QIOChannel {
+    Object parent;
+    unsigned int features; /* bitmask of QIOChannelFeatures */
+};
+
+/**
+ * QIOChannelClass:
+ *
+ * This class defines the contract that all subclasses
+ * must follow to provide specific channel implementations.
+ * The first five callbacks are mandatory to support, others
+ * provide additional optional features.
+ *
+ * Consult the corresponding public API docs for a description
+ * of the semantics of each callback
+ */
+struct QIOChannelClass {
+    ObjectClass parent;
+
+    /* Mandatory callbacks */
+    ssize_t (*io_writev)(QIOChannel *ioc,
+                         const struct iovec *iov,
+                         size_t niov,
+                         int *fds,
+                         size_t nfds,
+                         Error **errp);
+    ssize_t (*io_readv)(QIOChannel *ioc,
+                        const struct iovec *iov,
+                        size_t niov,
+                        int **fds,
+                        size_t *nfds,
+                        Error **errp);
+    int (*io_close)(QIOChannel *ioc,
+                    Error **errp);
+    GSource * (*io_create_watch)(QIOChannel *ioc,
+                                 GIOCondition condition);
+    int (*io_set_blocking)(QIOChannel *ioc,
+                           bool enabled,
+                           Error **errp);
+
+    /* Optional callbacks */
+    int (*io_shutdown)(QIOChannel *ioc,
+                       QIOChannelShutdown how,
+                       Error **errp);
+    void (*io_set_cork)(QIOChannel *ioc,
+                        bool enabled);
+    void (*io_set_delay)(QIOChannel *ioc,
+                         bool enabled);
+    off_t (*io_seek)(QIOChannel *ioc,
+                     off_t offset,
+                     int whence,
+                     Error **errp);
+};
+
+/* General I/O handling functions */
+
+/**
+ * qio_channel_has_feature:
+ * @ioc: the channel object
+ * @feature: the feature to check support of
+ *
+ * Determine whether the channel implementation supports
+ * the optional feature named in @feature.
+ *
+ * Returns: true if supported, false otherwise.
+ */
+bool qio_channel_has_feature(QIOChannel *ioc,
+                             QIOChannelFeature feature);
+
+/**
+ * qio_channel_readv_full:
+ * @ioc: the channel object
+ * @iov: the array of memory regions to read data into
+ * @niov: the length of the @iov array
+ * @fds: pointer to an array that will received file handles
+ * @nfds: pointer filled with number of elements in @fds on return
+ * @errp: pointer to an uninitialized error object
+ *
+ * Read data from the IO channel, storing it in the
+ * memory regions referenced by @iov. Each element
+ * in the @iov will be fully populated with data
+ * before the next one is used. The @niov parameter
+ * specifies the total number of elements in @iov.
+ *
+ * It is not required for all @iov to be filled with
+ * data. If the channel is in blocking mode, at least
+ * one byte of data will be read, but no more is
+ * guaranteed. If the channel is non-blocking and no
+ * data is available, it will return QIO_CHANNEL_ERR_BLOCK
+ *
+ * If the channel has passed any file descriptors,
+ * the @fds array pointer will be allocated and
+ * the elements filled with the received file
+ * descriptors. The @nfds pointer will be updated
+ * to indicate the size of the @fds array that
+ * 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.
+ *
+ * It is an error to pass a non-NULL @fds parameter
+ * unless qio_channel_has_feature() returns a true
+ * value for the QIO_CHANNEL_FEATURE_FD_PASS constant.
+ *
+ * Returns: the number of bytes read, or -1 on error,
+ * or QIO_CHANNEL_ERR_BLOCK if no data is available
+ * and the channel is non-blocking
+ */
+ssize_t qio_channel_readv_full(QIOChannel *ioc,
+                               const struct iovec *iov,
+                               size_t niov,
+                               int **fds,
+                               size_t *nfds,
+                               Error **errp);
+
+
+/**
+ * qio_channel_writev_full:
+ * @ioc: the channel object
+ * @iov: the array of memory regions to write data from
+ * @niov: the length of the @iov array
+ * @fds: an array of file handles to send
+ * @nfds: number of file handles in @fds
+ * @errp: pointer to an uninitialized error object
+ *
+ * Write data to the IO channel, reading it from the
+ * memory regions referenced by @iov. Each element
+ * in the @iov will be fully sent, before the next
+ * one is used. The @niov parameter specifies the
+ * total number of elements in @iov.
+ *
+ * It is not required for all @iov data to be fully
+ * sent. If the channel is in blocking mode, at least
+ * one byte of data will be sent, but no more is
+ * guaranteed. If the channel is non-blocking and no
+ * data can be sent, it will return QIO_CHANNEL_ERR_BLOCK
+ *
+ * If there are file descriptors to send, the @fds
+ * array should be non-NULL and provide the handles.
+ * All file descriptors will be sent if at least one
+ * byte of data was sent.
+ *
+ * It is an error to pass a non-NULL @fds parameter
+ * unless qio_channel_has_feature() returns a true
+ * value for the QIO_CHANNEL_FEATURE_FD_PASS constant.
+ *
+ * Returns: the number of bytes sent, or -1 on error,
+ * or QIO_CHANNEL_ERR_BLOCK if no data is can be sent
+ * and the channel is non-blocking
+ */
+ssize_t qio_channel_writev_full(QIOChannel *ioc,
+                                const struct iovec *iov,
+                                size_t niov,
+                                int *fds,
+                                size_t nfds,
+                                Error **errp);
+
+/**
+ * qio_channel_readv:
+ * @ioc: the channel object
+ * @iov: the array of memory regions to read data into
+ * @niov: the length of the @iov array
+ * @errp: pointer to an uninitialized error object
+ *
+ * Behaves as qio_channel_readv_full() but does not support
+ * receiving of file handles.
+ */
+ssize_t qio_channel_readv(QIOChannel *ioc,
+                          const struct iovec *iov,
+                          size_t niov,
+                          Error **errp);
+
+/**
+ * qio_channel_writev:
+ * @ioc: the channel object
+ * @iov: the array of memory regions to write data from
+ * @niov: the length of the @iov array
+ * @errp: pointer to an uninitialized error object
+ *
+ * Behaves as qio_channel_writev_full() but does not support
+ * sending of file handles.
+ */
+ssize_t qio_channel_writev(QIOChannel *ioc,
+                           const struct iovec *iov,
+                           size_t niov,
+                           Error **errp);
+
+/**
+ * qio_channel_readv:
+ * @ioc: the channel object
+ * @buf: the memory region to read data into
+ * @buflen: the length of @buf
+ * @errp: pointer to an uninitialized error object
+ *
+ * Behaves as qio_channel_readv_full() but does not support
+ * receiving of file handles, and only supports reading into
+ * a single memory region.
+ */
+ssize_t qio_channel_read(QIOChannel *ioc,
+                         char *buf,
+                         size_t buflen,
+                         Error **errp);
+
+/**
+ * qio_channel_writev:
+ * @ioc: the channel object
+ * @buf: the memory regions to send data from
+ * @buflen: the length of @buf
+ * @errp: pointer to an uninitialized error object
+ *
+ * Behaves as qio_channel_writev_full() but does not support
+ * sending of file handles, and only supports writing from a
+ * single memory region.
+ */
+ssize_t qio_channel_write(QIOChannel *ioc,
+                          const char *buf,
+                          size_t buflen,
+                          Error **errp);
+
+/**
+ * qio_channel_set_blocking:
+ * @ioc: the channel object
+ * @enabled: the blocking flag state
+ * @errp: pointer to an uninitialized error object
+ *
+ * If @enabled is true, then the channel is put into
+ * blocking mode, otherwise it will be non-blocking.
+ *
+ * In non-blocking mode, read/write operations may
+ * return QIO_CHANNEL_ERR_BLOCK if they would otherwise
+ * block on I/O
+ */
+int qio_channel_set_blocking(QIOChannel *ioc,
+                             bool enabled,
+                             Error **errp);
+
+/**
+ * qio_channel_close:
+ * @ioc: the channel object
+ * @errp: pointer to an uninitialized error object
+ *
+ * Close the channel, flushing any pending I/O
+ *
+ * Returns: 0 on success, -1 on error
+ */
+int qio_channel_close(QIOChannel *ioc,
+                      Error **errp);
+
+/**
+ * qio_channel_shutdown:
+ * @ioc: the channel object
+ * @how: the direction to shutdown
+ * @errp: pointer to an uninitialized error object
+ *
+ * Shutdowns transmission and/or receiving of data
+ * without closing the underlying transport.
+ *
+ * Not all implementations will support this facility,
+ * so may report an error. To avoid errors, the
+ * caller may check for the feature flag
+ * QIO_CHANNEL_FEATURE_SHUTDOWN prior to calling
+ * this method.
+ *
+ * Returns: 0 on success, -1 on error
+ */
+int qio_channel_shutdown(QIOChannel *ioc,
+                         QIOChannelShutdown how,
+                         Error **errp);
+
+/**
+ * qio_channel_set_delay:
+ * @ioc: the channel object
+ * @enabled: the new flag state
+ *
+ * Controls whether the underlying transport is
+ * permitted to delay writes in order to merge
+ * small packets. If @enabled is true, then the
+ * writes may be delayed in order to opportunistically
+ * merge small packets into larger ones. If @enabled
+ * is false, writes are dispatched immediately with
+ * no delay.
+ *
+ * When @enabled is false, applications may wish to
+ * use the qio_channel_set_cork() method to explicitly
+ * control write merging.
+ *
+ * On channels which are backed by a socket, this
+ * API corresponds to the inverse of TCP_NODELAY flag,
+ * controlling whether the Nagle algorithm is active.
+ *
+ * This setting is merely a hint, so implementations are
+ * free to ignore this without it being considered an
+ * error.
+ */
+void qio_channel_set_delay(QIOChannel *ioc,
+                           bool enabled);
+
+/**
+ * qio_channel_set_cork:
+ * @ioc: the channel object
+ * @enabled: the new flag state
+ *
+ * Controls whether the underlying transport is
+ * permitted to dispatch data that is written.
+ * If @enabled is true, then any data written will
+ * be queued in local buffers until @enabled is
+ * set to false once again.
+ *
+ * This feature is typically used when the automatic
+ * write coalescing facility is disabled via the
+ * qio_channel_set_delay() method.
+ *
+ * On channels which are backed by a socket, this
+ * API corresponds to the TCP_CORK flag.
+ *
+ * This setting is merely a hint, so implementations are
+ * free to ignore this without it being considered an
+ * error.
+ */
+void qio_channel_set_cork(QIOChannel *ioc,
+                          bool enabled);
+
+
+/**
+ * qio_channel_seek:
+ * @ioc: the channel object
+ * @offset: the position to seek to, relative to @whence
+ * @whence: one of the (POSIX) SEEK_* constants listed below
+ * @errp: pointer to an uninitialized error object
+ *
+ * Moves the current I/O position within the channel
+ * @ioc, to be @offset. The value of @offset is
+ * interpreted relative to @whence:
+ *
+ * SEEK_SET - the position is set to @offset bytes
+ * SEEK_CUR - the position is moved by @offset bytes
+ * SEEK_END - the position is set to end of the file plus @offset bytes
+ *
+ * Not all implementations will support this facility,
+ * so may report an error.
+ *
+ * Returns: the new position on success, (off_t)-1 on failure
+ */
+off_t qio_channel_io_seek(QIOChannel *ioc,
+                          off_t offset,
+                          int whence,
+                          Error **errp);
+
+
+/**
+ * qio_channel_create_watch:
+ * @ioc: the channel object
+ * @condition: the I/O condition to monitor
+ *
+ * Create a new main loop source that is used to watch
+ * for the I/O condition @condition. Typically the
+ * qio_channel_add_watch() method would be used instead
+ * of this, since it directly attaches a callback to
+ * the source
+ *
+ * Returns: the new main loop source.
+ */
+GSource *qio_channel_create_watch(QIOChannel *ioc,
+                                  GIOCondition condition);
+
+/**
+ * qio_channel_add_watch:
+ * @ioc: the channel object
+ * @condition: the I/O condition to monitor
+ * @func: callback to invoke when the source becomes ready
+ * @user_data: opaque data to pass to @func
+ * @notify: callback to free @user_data
+ *
+ * Create a new main loop source that is used to watch
+ * for the I/O condition @condition. The callback @func
+ * will be registered against the source, to be invoked
+ * when the source becomes ready. The optional @user_data
+ * will be passed to @func when it is invoked. The @notify
+ * callback will be used to free @user_data when the
+ * watch is deleted
+ *
+ * The returned source ID can be used with g_source_remove()
+ * to remove and free the source when no longer required.
+ * Alternatively the @func callback can return a FALSE
+ * value.
+ *
+ * Returns: the source ID
+ */
+guint qio_channel_add_watch(QIOChannel *ioc,
+                            GIOCondition condition,
+                            QIOChannelFunc func,
+                            gpointer user_data,
+                            GDestroyNotify notify);
+
+
+/**
+ * qio_channel_yield:
+ * @ioc: the channel object
+ * @condition: the I/O condition to wait for
+ *
+ * Yields execution from the current coroutine until
+ * the condition indicated by @condition becomes
+ * available.
+ *
+ * This must only be called from coroutine context
+ */
+void qio_channel_yield(QIOChannel *ioc,
+                       GIOCondition condition);
+
+/**
+ * qio_channel_wait:
+ * @ioc: the channel object
+ * @condition: the I/O condition to wait for
+ *
+ * Block execution from the current thread until
+ * the condition indicated by @condition becomes
+ * available.
+ *
+ * This will enter a nested event loop to perform
+ * the wait.
+ */
+void qio_channel_wait(QIOChannel *ioc,
+                      GIOCondition condition);
+
+#endif /* QIO_CHANNEL_H__ */

io/Makefile.objs

@@ -0,0 +1 @@
+io-obj-y = channel.o

io/channel.c

@@ -0,0 +1,291 @@
+/*
+ * QEMU I/O channels
+ *
+ * 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.h"
+#include "qemu/coroutine.h"
+
+bool qio_channel_has_feature(QIOChannel *ioc,
+                             QIOChannelFeature feature)
+{
+    return ioc->features & (1 << feature);
+}
+
+
+ssize_t qio_channel_readv_full(QIOChannel *ioc,
+                               const struct iovec *iov,
+                               size_t niov,
+                               int **fds,
+                               size_t *nfds,
+                               Error **errp)
+{
+    QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+
+    if ((fds || nfds) &&
+        !(ioc->features & (1 << QIO_CHANNEL_FEATURE_FD_PASS))) {
+        error_setg_errno(errp, EINVAL,
+                         "Channel does not support file descriptor passing");
+        return -1;
+    }
+
+    return klass->io_readv(ioc, iov, niov, fds, nfds, errp);
+}
+
+
+ssize_t qio_channel_writev_full(QIOChannel *ioc,
+                                const struct iovec *iov,
+                                size_t niov,
+                                int *fds,
+                                size_t nfds,
+                                Error **errp)
+{
+    QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+
+    if ((fds || nfds) &&
+        !(ioc->features & (1 << QIO_CHANNEL_FEATURE_FD_PASS))) {
+        error_setg_errno(errp, EINVAL,
+                         "Channel does not support file descriptor passing");
+        return -1;
+    }
+
+    return klass->io_writev(ioc, iov, niov, fds, nfds, errp);
+}
+
+
+ssize_t qio_channel_readv(QIOChannel *ioc,
+                          const struct iovec *iov,
+                          size_t niov,
+                          Error **errp)
+{
+    return qio_channel_readv_full(ioc, iov, niov, NULL, NULL, errp);
+}
+
+
+ssize_t qio_channel_writev(QIOChannel *ioc,
+                           const struct iovec *iov,
+                           size_t niov,
+                           Error **errp)
+{
+    return qio_channel_writev_full(ioc, iov, niov, NULL, 0, errp);
+}
+
+
+ssize_t qio_channel_read(QIOChannel *ioc,
+                         char *buf,
+                         size_t buflen,
+                         Error **errp)
+{
+    struct iovec iov = { .iov_base = buf, .iov_len = buflen };
+    return qio_channel_readv_full(ioc, &iov, 1, NULL, NULL, errp);
+}
+
+
+ssize_t qio_channel_write(QIOChannel *ioc,
+                          const char *buf,
+                          size_t buflen,
+                          Error **errp)
+{
+    struct iovec iov = { .iov_base = (char *)buf, .iov_len = buflen };
+    return qio_channel_writev_full(ioc, &iov, 1, NULL, 0, errp);
+}
+
+
+int qio_channel_set_blocking(QIOChannel *ioc,
+                              bool enabled,
+                              Error **errp)
+{
+    QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+    return klass->io_set_blocking(ioc, enabled, errp);
+}
+
+
+int qio_channel_close(QIOChannel *ioc,
+                      Error **errp)
+{
+    QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+    return klass->io_close(ioc, errp);
+}
+
+
+GSource *qio_channel_create_watch(QIOChannel *ioc,
+                                  GIOCondition condition)
+{
+    QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+    return klass->io_create_watch(ioc, condition);
+}
+
+
+guint qio_channel_add_watch(QIOChannel *ioc,
+                            GIOCondition condition,
+                            QIOChannelFunc func,
+                            gpointer user_data,
+                            GDestroyNotify notify)
+{
+    GSource *source;
+    guint id;
+
+    source = qio_channel_create_watch(ioc, condition);
+
+    g_source_set_callback(source, (GSourceFunc)func, user_data, notify);
+
+    id = g_source_attach(source, NULL);
+    g_source_unref(source);
+
+    return id;
+}
+
+
+int qio_channel_shutdown(QIOChannel *ioc,
+                         QIOChannelShutdown how,
+                         Error **errp)
+{
+    QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+
+    if (!klass->io_shutdown) {
+        error_setg(errp, "Data path shutdown not supported");
+        return -1;
+    }
+
+    return klass->io_shutdown(ioc, how, errp);
+}
+
+
+void qio_channel_set_delay(QIOChannel *ioc,
+                           bool enabled)
+{
+    QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+
+    if (klass->io_set_delay) {
+        klass->io_set_delay(ioc, enabled);
+    }
+}
+
+
+void qio_channel_set_cork(QIOChannel *ioc,
+                          bool enabled)
+{
+    QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+
+    if (klass->io_set_cork) {
+        klass->io_set_cork(ioc, enabled);
+    }
+}
+
+
+off_t qio_channel_io_seek(QIOChannel *ioc,
+                          off_t offset,
+                          int whence,
+                          Error **errp)
+{
+    QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
+
+    if (!klass->io_seek) {
+        error_setg(errp, "Channel does not support random access");
+        return -1;
+    }
+
+    return klass->io_seek(ioc, offset, whence, errp);
+}
+
+
+typedef struct QIOChannelYieldData QIOChannelYieldData;
+struct QIOChannelYieldData {
+    QIOChannel *ioc;
+    Coroutine *co;
+};
+
+
+static gboolean qio_channel_yield_enter(QIOChannel *ioc,
+                                        GIOCondition condition,
+                                        gpointer opaque)
+{
+    QIOChannelYieldData *data = opaque;
+    qemu_coroutine_enter(data->co, NULL);
+    return FALSE;
+}
+
+
+void coroutine_fn qio_channel_yield(QIOChannel *ioc,
+                                    GIOCondition condition)
+{
+    QIOChannelYieldData data;
+
+    assert(qemu_in_coroutine());
+    data.ioc = ioc;
+    data.co = qemu_coroutine_self();
+    qio_channel_add_watch(ioc,
+                          condition,
+                          qio_channel_yield_enter,
+                          &data,
+                          NULL);
+    qemu_coroutine_yield();
+}
+
+
+static gboolean qio_channel_wait_complete(QIOChannel *ioc,
+                                          GIOCondition condition,
+                                          gpointer opaque)
+{
+    GMainLoop *loop = opaque;
+
+    g_main_loop_quit(loop);
+    return FALSE;
+}
+
+
+void qio_channel_wait(QIOChannel *ioc,
+                      GIOCondition condition)
+{
+    GMainContext *ctxt = g_main_context_new();
+    GMainLoop *loop = g_main_loop_new(ctxt, TRUE);
+    GSource *source;
+
+    source = qio_channel_create_watch(ioc, condition);
+
+    g_source_set_callback(source,
+                          (GSourceFunc)qio_channel_wait_complete,
+                          loop,
+                          NULL);
+
+    g_source_attach(source, ctxt);
+
+    g_main_loop_run(loop);
+
+    g_source_unref(source);
+    g_main_loop_unref(loop);
+    g_main_context_unref(ctxt);
+}
+
+
+static const TypeInfo qio_channel_info = {
+    .parent = TYPE_OBJECT,
+    .name = TYPE_QIO_CHANNEL,
+    .instance_size = sizeof(QIOChannel),
+    .abstract = true,
+    .class_size = sizeof(QIOChannelClass),
+};
+
+
+static void qio_channel_register_types(void)
+{
+    type_register_static(&qio_channel_info);
+}
+
+
+type_init(qio_channel_register_types);