[Qemu-devel] [PATCH v2 16/16] io: add QIOChannelBuffer class

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

Add a QIOChannel subclass that is capable of performing I/O
to/from a memory buffer. This implementation does not attempt
to support concurrent readers & writers. It is designed for
serialized access where by a single thread at a time may write
data, seek and then read data back out.

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
---
 include/io/channel-buffer.h |  59 ++++++++++
 io/Makefile.objs            |   1 +
 io/channel-buffer.c         | 255 ++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 315 insertions(+)
 create mode 100644 include/io/channel-buffer.h
 create mode 100644 io/channel-buffer.c

diff --git a/include/io/channel-buffer.h b/include/io/channel-buffer.h
new file mode 100644
index 0000000..1e0f6c2
--- /dev/null
+++ b/include/io/channel-buffer.h
@@ -0,0 +1,59 @@
+/*
+ * QEMU I/O channels memory buffer driver
+ *
+ * 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_BUFFER_H__
+#define QIO_CHANNEL_BUFFER_H__
+
+#include "io/channel.h"
+
+#define TYPE_QIO_CHANNEL_BUFFER "qio-channel-buffer"
+#define QIO_CHANNEL_BUFFER(obj)                                     \
+    OBJECT_CHECK(QIOChannelBuffer, (obj), TYPE_QIO_CHANNEL_BUFFER)
+
+typedef struct QIOChannelBuffer QIOChannelBuffer;
+
+/**
+ * QIOChannelBuffer:
+ *
+ * The QIOChannelBuffer object provides a channel implementation
+ * that is able to perform I/O to/from a memory buffer.
+ *
+ */
+
+struct QIOChannelBuffer {
+    QIOChannel parent;
+    size_t capacity; /* Total allocated memory */
+    size_t usage;    /* Current size of data */
+    size_t offset;   /* Offset for future I/O ops */
+    char *data;
+};
+
+
+/**
+ * qio_channel_buffer_new:
+ *
+ * Allocate a new buffer which is initially empty
+ *
+ * Returns: the new channel object
+ */
+QIOChannelBuffer *
+qio_channel_buffer_new(void);
+
+#endif /* QIO_CHANNEL_BUFFER_H__ */
diff --git a/io/Makefile.objs b/io/Makefile.objs
index 1a58ccb..0e3de31 100644
--- a/io/Makefile.objs
+++ b/io/Makefile.objs
@@ -1,4 +1,5 @@
 io-obj-y = channel.o
+io-obj-y += channel-buffer.o
 io-obj-y += channel-command.o
 io-obj-y += channel-file.o
 io-obj-y += channel-socket.o
diff --git a/io/channel-buffer.c b/io/channel-buffer.c
new file mode 100644
index 0000000..8d85032
--- /dev/null
+++ b/io/channel-buffer.c
@@ -0,0 +1,255 @@
+/*
+ * QEMU I/O channels memory buffer driver
+ *
+ * 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-buffer.h"
+#include "io/channel-watch.h"
+#include "qemu/sockets.h"
+#include "trace.h"
+
+QIOChannelBuffer *
+qio_channel_buffer_new(void)
+{
+    QIOChannelBuffer *ioc;
+
+    ioc = QIO_CHANNEL_BUFFER(object_new(TYPE_QIO_CHANNEL_BUFFER));
+
+    return ioc;
+}
+
+
+static void qio_channel_buffer_finalize(Object *obj)
+{
+    QIOChannelBuffer *ioc = QIO_CHANNEL_BUFFER(obj);
+    g_free(ioc->data);
+    ioc->capacity = ioc->usage = ioc->offset = 0;
+}
+
+
+static ssize_t qio_channel_buffer_readv(QIOChannel *ioc,
+                                        const struct iovec *iov,
+                                        size_t niov,
+                                        int **fds,
+                                        size_t *nfds,
+                                        Error **errp)
+{
+    QIOChannelBuffer *bioc = QIO_CHANNEL_BUFFER(ioc);
+    ssize_t ret = 0;
+    size_t i;
+
+    if (fds || nfds) {
+        error_setg_errno(errp, EINVAL,
+                         "Channel does not support buffer descriptor passing");
+        return -1;
+    }
+
+    for (i = 0; i < niov; i++) {
+        size_t want = iov[i].iov_len;
+        if (bioc->offset >= bioc->usage) {
+            break;
+        }
+        if ((bioc->offset + want) > bioc->usage)  {
+            want = bioc->usage - bioc->offset;
+        }
+        memcpy(iov[i].iov_base, bioc->data + bioc->offset, want);
+        ret += want;
+    }
+
+    return ret;
+}
+
+static ssize_t qio_channel_buffer_writev(QIOChannel *ioc,
+                                         const struct iovec *iov,
+                                         size_t niov,
+                                         int *fds,
+                                         size_t nfds,
+                                         Error **errp)
+{
+    QIOChannelBuffer *bioc = QIO_CHANNEL_BUFFER(ioc);
+    ssize_t ret = 0;
+    size_t i;
+    size_t towrite = 0;
+
+    if (fds || nfds) {
+        error_setg_errno(errp, EINVAL,
+                         "Channel does not support buffer descriptor passing");
+        return -1;
+    }
+
+    for (i = 0; i < niov; i++) {
+        towrite += iov[i].iov_len;
+    }
+
+    if ((bioc->offset + towrite) > bioc->capacity) {
+        bioc->capacity = bioc->offset + towrite;
+        bioc->data = g_realloc(bioc->data, bioc->capacity);
+    }
+
+    if (bioc->offset > bioc->usage) {
+        memset(bioc->data, 0, bioc->offset - bioc->usage);
+        bioc->usage = bioc->offset;
+    }
+
+    for (i = 0; i < niov; i++) {
+        memcpy(bioc->data + bioc->usage,
+               iov[i].iov_base,
+               iov[i].iov_len);
+        bioc->usage += iov[i].iov_len;
+        bioc->offset += iov[i].iov_len;
+        ret += iov[i].iov_len;
+    }
+
+    return ret;
+}
+
+static int qio_channel_buffer_set_blocking(QIOChannel *ioc G_GNUC_UNUSED,
+                                           bool enabled G_GNUC_UNUSED,
+                                           Error **errp G_GNUC_UNUSED)
+{
+    return 0;
+}
+
+
+static off64_t qio_channel_buffer_seek(QIOChannel *ioc,
+                                       off64_t offset,
+                                       int whence,
+                                       Error **errp)
+{
+    QIOChannelBuffer *bioc = QIO_CHANNEL_BUFFER(ioc);
+
+    bioc->offset = offset;
+
+    return offset;
+}
+
+
+static int qio_channel_buffer_close(QIOChannel *ioc,
+                                    Error **errp)
+{
+    QIOChannelBuffer *bioc = QIO_CHANNEL_BUFFER(ioc);
+
+    g_free(bioc->data);
+    bioc->capacity = bioc->usage = bioc->offset = 0;
+
+    return 0;
+}
+
+
+typedef struct QIOChannelBufferSource QIOChannelBufferSource;
+struct QIOChannelBufferSource {
+    GSource parent;
+    QIOChannelBuffer *bioc;
+    GIOCondition condition;
+};
+
+static gboolean
+qio_channel_buffer_source_prepare(GSource *source,
+                                  gint *timeout)
+{
+    QIOChannelBufferSource *bsource = (QIOChannelBufferSource *)source;
+
+    *timeout = -1;
+
+    return (G_IO_IN | G_IO_OUT) & bsource->condition;
+}
+
+static gboolean
+qio_channel_buffer_source_check(GSource *source)
+{
+    QIOChannelBufferSource *bsource = (QIOChannelBufferSource *)source;
+
+    return (G_IO_IN | G_IO_OUT) & bsource->condition;
+}
+
+static gboolean
+qio_channel_buffer_source_dispatch(GSource *source,
+                                   GSourceFunc callback,
+                                   gpointer user_data)
+{
+    QIOChannelFunc func = (QIOChannelFunc)callback;
+    QIOChannelBufferSource *bsource = (QIOChannelBufferSource *)source;
+
+    return (*func)(QIO_CHANNEL(bsource->bioc),
+                   ((G_IO_IN | G_IO_OUT) & bsource->condition),
+                   user_data);
+}
+
+static void
+qio_channel_buffer_source_finalize(GSource *source)
+{
+    QIOChannelBufferSource *ssource = (QIOChannelBufferSource *)source;
+
+    object_unref(OBJECT(ssource->bioc));
+}
+
+GSourceFuncs qio_channel_buffer_source_funcs = {
+    qio_channel_buffer_source_prepare,
+    qio_channel_buffer_source_check,
+    qio_channel_buffer_source_dispatch,
+    qio_channel_buffer_source_finalize
+};
+
+static GSource *qio_channel_buffer_create_watch(QIOChannel *ioc,
+                                                GIOCondition condition)
+{
+    QIOChannelBuffer *bioc = QIO_CHANNEL_BUFFER(ioc);
+    QIOChannelBufferSource *ssource;
+    GSource *source;
+
+    source = g_source_new(&qio_channel_buffer_source_funcs,
+                          sizeof(QIOChannelBufferSource));
+    g_source_set_name(source, "QIOChannelBuffer");
+    ssource = (QIOChannelBufferSource *)source;
+
+    ssource->bioc = bioc;
+    object_ref(OBJECT(bioc));
+
+    ssource->condition = condition;
+
+    return source;
+}
+
+
+static void qio_channel_buffer_class_init(ObjectClass *klass,
+                                          void *class_data G_GNUC_UNUSED)
+{
+    QIOChannelClass *ioc_klass = QIO_CHANNEL_CLASS(klass);
+
+    ioc_klass->io_writev = qio_channel_buffer_writev;
+    ioc_klass->io_readv = qio_channel_buffer_readv;
+    ioc_klass->io_set_blocking = qio_channel_buffer_set_blocking;
+    ioc_klass->io_seek = qio_channel_buffer_seek;
+    ioc_klass->io_close = qio_channel_buffer_close;
+    ioc_klass->io_create_watch = qio_channel_buffer_create_watch;
+}
+
+static const TypeInfo qio_channel_buffer_info = {
+    .parent = TYPE_QIO_CHANNEL,
+    .name = TYPE_QIO_CHANNEL_BUFFER,
+    .instance_size = sizeof(QIOChannelBuffer),
+    .instance_finalize = qio_channel_buffer_finalize,
+    .class_init = qio_channel_buffer_class_init,
+};
+
+static void qio_channel_buffer_register_types(void)
+{
+    type_register_static(&qio_channel_buffer_info);
+}
+
+type_init(qio_channel_buffer_register_types);
-- 
2.4.3