migration: introduce a QIOChannel impl for BlockDriverState VMState

Introduce a QIOChannelBlock class that exposes the BlockDriverState
VMState region for I/O.

This is kept in the migration/ directory rather than io/, to avoid
a mutual dependancy between block/ <-> io/ directories. Also the
VMState should only be used by the migration code.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
  dgilbert: Fixed coding style in qio_channel_block_close

migration/channel-block.c

@@ -0,0 +1,195 @@
+/*
+ * QEMU I/O channels block driver
+ *
+ * Copyright (c) 2022 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 "qemu/osdep.h"
+#include "migration/channel-block.h"
+#include "qapi/error.h"
+#include "block/block.h"
+#include "trace.h"
+
+QIOChannelBlock *
+qio_channel_block_new(BlockDriverState *bs)
+{
+    QIOChannelBlock *ioc;
+
+    ioc = QIO_CHANNEL_BLOCK(object_new(TYPE_QIO_CHANNEL_BLOCK));
+
+    bdrv_ref(bs);
+    ioc->bs = bs;
+
+    return ioc;
+}
+
+
+static void
+qio_channel_block_finalize(Object *obj)
+{
+    QIOChannelBlock *ioc = QIO_CHANNEL_BLOCK(obj);
+
+    g_clear_pointer(&ioc->bs, bdrv_unref);
+}
+
+
+static ssize_t
+qio_channel_block_readv(QIOChannel *ioc,
+                        const struct iovec *iov,
+                        size_t niov,
+                        int **fds,
+                        size_t *nfds,
+                        Error **errp)
+{
+    QIOChannelBlock *bioc = QIO_CHANNEL_BLOCK(ioc);
+    QEMUIOVector qiov;
+    int ret;
+
+    qemu_iovec_init_external(&qiov, (struct iovec *)iov, niov);
+    ret = bdrv_readv_vmstate(bioc->bs, &qiov, bioc->offset);
+    if (ret < 0) {
+        return ret;
+    }
+
+    bioc->offset += qiov.size;
+    return qiov.size;
+}
+
+
+static ssize_t
+qio_channel_block_writev(QIOChannel *ioc,
+                         const struct iovec *iov,
+                         size_t niov,
+                         int *fds,
+                         size_t nfds,
+                         int flags,
+                         Error **errp)
+{
+    QIOChannelBlock *bioc = QIO_CHANNEL_BLOCK(ioc);
+    QEMUIOVector qiov;
+    int ret;
+
+    qemu_iovec_init_external(&qiov, (struct iovec *)iov, niov);
+    ret = bdrv_writev_vmstate(bioc->bs, &qiov, bioc->offset);
+    if (ret < 0) {
+        return ret;
+    }
+
+    bioc->offset += qiov.size;
+    return qiov.size;
+}
+
+
+static int
+qio_channel_block_set_blocking(QIOChannel *ioc,
+                               bool enabled,
+                               Error **errp)
+{
+    if (!enabled) {
+        error_setg(errp, "Non-blocking mode not supported for block devices");
+        return -1;
+    }
+    return 0;
+}
+
+
+static off_t
+qio_channel_block_seek(QIOChannel *ioc,
+                       off_t offset,
+                       int whence,
+                       Error **errp)
+{
+    QIOChannelBlock *bioc = QIO_CHANNEL_BLOCK(ioc);
+
+    switch (whence) {
+    case SEEK_SET:
+        bioc->offset = offset;
+        break;
+    case SEEK_CUR:
+        bioc->offset += whence;
+        break;
+    case SEEK_END:
+        error_setg(errp, "Size of VMstate region is unknown");
+        return (off_t)-1;
+    default:
+        g_assert_not_reached();
+    }
+
+    return bioc->offset;
+}
+
+
+static int
+qio_channel_block_close(QIOChannel *ioc,
+                        Error **errp)
+{
+    QIOChannelBlock *bioc = QIO_CHANNEL_BLOCK(ioc);
+    int rv = bdrv_flush(bioc->bs);
+
+    if (rv < 0) {
+        error_setg_errno(errp, -rv,
+                         "Unable to flush VMState");
+        return -1;
+    }
+
+    g_clear_pointer(&bioc->bs, bdrv_unref);
+    bioc->offset = 0;
+
+    return 0;
+}
+
+
+static void
+qio_channel_block_set_aio_fd_handler(QIOChannel *ioc,
+                                     AioContext *ctx,
+                                     IOHandler *io_read,
+                                     IOHandler *io_write,
+                                     void *opaque)
+{
+    /* XXX anything we can do here ? */
+}
+
+
+static void
+qio_channel_block_class_init(ObjectClass *klass,
+                             void *class_data G_GNUC_UNUSED)
+{
+    QIOChannelClass *ioc_klass = QIO_CHANNEL_CLASS(klass);
+
+    ioc_klass->io_writev = qio_channel_block_writev;
+    ioc_klass->io_readv = qio_channel_block_readv;
+    ioc_klass->io_set_blocking = qio_channel_block_set_blocking;
+    ioc_klass->io_seek = qio_channel_block_seek;
+    ioc_klass->io_close = qio_channel_block_close;
+    ioc_klass->io_set_aio_fd_handler = qio_channel_block_set_aio_fd_handler;
+}
+
+static const TypeInfo qio_channel_block_info = {
+    .parent = TYPE_QIO_CHANNEL,
+    .name = TYPE_QIO_CHANNEL_BLOCK,
+    .instance_size = sizeof(QIOChannelBlock),
+    .instance_finalize = qio_channel_block_finalize,
+    .class_init = qio_channel_block_class_init,
+};
+
+static void
+qio_channel_block_register_types(void)
+{
+    type_register_static(&qio_channel_block_info);
+}
+
+type_init(qio_channel_block_register_types);

migration/channel-block.h

@@ -0,0 +1,59 @@
+/*
+ * QEMU I/O channels block driver
+ *
+ * Copyright (c) 2022 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/>.
+ *
+ */
+
+#ifndef QIO_CHANNEL_BLOCK_H
+#define QIO_CHANNEL_BLOCK_H
+
+#include "io/channel.h"
+#include "qom/object.h"
+
+#define TYPE_QIO_CHANNEL_BLOCK "qio-channel-block"
+OBJECT_DECLARE_SIMPLE_TYPE(QIOChannelBlock, QIO_CHANNEL_BLOCK)
+
+
+/**
+ * QIOChannelBlock:
+ *
+ * The QIOChannelBlock object provides a channel implementation
+ * that is able to perform I/O on the BlockDriverState objects
+ * to the VMState region.
+ */
+
+struct QIOChannelBlock {
+    QIOChannel parent;
+    BlockDriverState *bs;
+    off_t offset;
+};
+
+
+/**
+ * qio_channel_block_new:
+ * @bs: the block driver state
+ *
+ * Create a new IO channel object that can perform
+ * I/O on a BlockDriverState object to the VMState
+ * region
+ *
+ * Returns: the new channel object
+ */
+QIOChannelBlock *
+qio_channel_block_new(BlockDriverState *bs);
+
+#endif /* QIO_CHANNEL_BLOCK_H */

migration/meson.build

@@ -13,6 +13,7 @@ softmmu_ss.add(migration_files)
 softmmu_ss.add(files(
   'block-dirty-bitmap.c',
   'channel.c',
+  'channel-block.c',
   'colo-failover.c',
   'colo.c',
   'exec.c',