Re: [PATCH 02/31] vhost: Add VhostShadowVirtqueue

[Eugenio Perez Martin]

On Fri, Jan 21, 2022 at 9:32 PM Eugenio Pérez <eperezma@redhat.com> wrote:
>
> Vhost shadow virtqueue (SVQ) is an intermediate jump for virtqueue
> notifications and buffers, allowing qemu to track them. While qemu is
> forwarding the buffers and virtqueue changes, it is able to commit the
> memory it's being dirtied, the same way regular qemu's VirtIO devices
> do.
>
> This commit only exposes basic SVQ allocation and free. Next patches of
> the series add functionality like notifications and buffers forwarding.
>
> Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
> ---
>  hw/virtio/vhost-shadow-virtqueue.h | 21 ++++++++++
>  hw/virtio/vhost-shadow-virtqueue.c | 64 ++++++++++++++++++++++++++++++
>  hw/virtio/meson.build              |  2 +-
>  3 files changed, 86 insertions(+), 1 deletion(-)
>  create mode 100644 hw/virtio/vhost-shadow-virtqueue.h
>  create mode 100644 hw/virtio/vhost-shadow-virtqueue.c
>
> diff --git a/hw/virtio/vhost-shadow-virtqueue.h 
> b/hw/virtio/vhost-shadow-virtqueue.h
> new file mode 100644
> index 0000000000..61ea112002
> --- /dev/null
> +++ b/hw/virtio/vhost-shadow-virtqueue.h
> @@ -0,0 +1,21 @@
> +/*
> + * vhost shadow virtqueue
> + *
> + * SPDX-FileCopyrightText: Red Hat, Inc. 2021
> + * SPDX-FileContributor: Author: Eugenio Pérez <eperezma@redhat.com>
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#ifndef VHOST_SHADOW_VIRTQUEUE_H
> +#define VHOST_SHADOW_VIRTQUEUE_H
> +
> +#include "hw/virtio/vhost.h"
> +
> +typedef struct VhostShadowVirtqueue VhostShadowVirtqueue;
> +
> +VhostShadowVirtqueue *vhost_svq_new(void);
> +
> +void vhost_svq_free(VhostShadowVirtqueue *vq);
> +
> +#endif
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c 
> b/hw/virtio/vhost-shadow-virtqueue.c
> new file mode 100644
> index 0000000000..5ee7b401cb
> --- /dev/null
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -0,0 +1,64 @@
> +/*
> + * vhost shadow virtqueue
> + *
> + * SPDX-FileCopyrightText: Red Hat, Inc. 2021
> + * SPDX-FileContributor: Author: Eugenio Pérez <eperezma@redhat.com>
> + *
> + * SPDX-License-Identifier: GPL-2.0-or-later
> + */
> +
> +#include "qemu/osdep.h"
> +#include "hw/virtio/vhost-shadow-virtqueue.h"
> +
> +#include "qemu/error-report.h"
> +#include "qemu/event_notifier.h"
> +
> +/* Shadow virtqueue to relay notifications */
> +typedef struct VhostShadowVirtqueue {

This is already typedef as VhostShadowVirtqueue in the header, so I
will remove it here for the next version.

> +    /* Shadow kick notifier, sent to vhost */
> +    EventNotifier hdev_kick;
> +    /* Shadow call notifier, sent to vhost */
> +    EventNotifier hdev_call;
> +} VhostShadowVirtqueue;
> +
> +/**
> + * Creates vhost shadow virtqueue, and instruct vhost device to use the 
> shadow
> + * methods and file descriptors.
> + */
> +VhostShadowVirtqueue *vhost_svq_new(void)
> +{
> +    g_autofree VhostShadowVirtqueue *svq = g_new0(VhostShadowVirtqueue, 1);
> +    int r;
> +
> +    r = event_notifier_init(&svq->hdev_kick, 0);
> +    if (r != 0) {
> +        error_report("Couldn't create kick event notifier: %s",
> +                     strerror(errno));
> +        goto err_init_hdev_kick;
> +    }
> +
> +    r = event_notifier_init(&svq->hdev_call, 0);
> +    if (r != 0) {
> +        error_report("Couldn't create call event notifier: %s",
> +                     strerror(errno));
> +        goto err_init_hdev_call;
> +    }
> +
> +    return g_steal_pointer(&svq);
> +
> +err_init_hdev_call:
> +    event_notifier_cleanup(&svq->hdev_kick);
> +
> +err_init_hdev_kick:
> +    return NULL;
> +}
> +
> +/**
> + * Free the resources of the shadow virtqueue.
> + */
> +void vhost_svq_free(VhostShadowVirtqueue *vq)
> +{
> +    event_notifier_cleanup(&vq->hdev_kick);
> +    event_notifier_cleanup(&vq->hdev_call);
> +    g_free(vq);
> +}
> diff --git a/hw/virtio/meson.build b/hw/virtio/meson.build
> index 521f7d64a8..2dc87613bc 100644
> --- a/hw/virtio/meson.build
> +++ b/hw/virtio/meson.build
> @@ -11,7 +11,7 @@ softmmu_ss.add(when: 'CONFIG_ALL', if_true: 
> files('vhost-stub.c'))
>
>  virtio_ss = ss.source_set()
>  virtio_ss.add(files('virtio.c'))
> -virtio_ss.add(when: 'CONFIG_VHOST', if_true: files('vhost.c', 
> 'vhost-backend.c'))
> +virtio_ss.add(when: 'CONFIG_VHOST', if_true: files('vhost.c', 
> 'vhost-backend.c', 'vhost-shadow-virtqueue.c'))
>  virtio_ss.add(when: 'CONFIG_VHOST_USER', if_true: files('vhost-user.c'))
>  virtio_ss.add(when: 'CONFIG_VHOST_VDPA', if_true: files('vhost-vdpa.c'))
>  virtio_ss.add(when: 'CONFIG_VIRTIO_BALLOON', if_true: 
> files('virtio-balloon.c'))
> --
> 2.27.0
>
>