Re: [PATCH v2 09/21] migration: introduce a QIOChannel impl for BlockDriverState VMState

[Juan Quintela <quintela@redhat.com>]

Daniel P. Berrangé <berrange@redhat.com> wrote:
> 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.
>
> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

I will maggically charge this to a:

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

O:-)

> ---
>  migration/channel-block.c | 195 ++++++++++++++++++++++++++++++++++++++
>  migration/channel-block.h |  59 ++++++++++++
>  migration/meson.build     |   1 +
>  3 files changed, 255 insertions(+)
>  create mode 100644 migration/channel-block.c
>  create mode 100644 migration/channel-block.h
>
> diff --git a/migration/channel-block.c b/migration/channel-block.c
> new file mode 100644
> index 0000000000..ad52342c10
> --- /dev/null
> +++ b/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;
> +
> +    if ((rv = bdrv_flush(bioc->bs)) < 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);
> diff --git a/migration/channel-block.h b/migration/channel-block.h
> new file mode 100644
> index 0000000000..31673824e6
> --- /dev/null
> +++ b/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 */
> diff --git a/migration/meson.build b/migration/meson.build
> index 6880b61b10..8d309f5849 100644
> --- a/migration/meson.build
> +++ b/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',