linux-kernel - Re: [PATCH] virtio_pci: move structure to a header

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Date:   Wed, 1 Nov 2023 08:38:05 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        virtualization@...ts.linux-foundation.org
Subject: Re: [PATCH] virtio_pci: move structure to a header

On Wed, Nov 1, 2023 at 12:20 AM Michael S. Tsirkin <mst@...hat.com> wrote:
>
> These are guest/host interfaces so belong in the header
> where e.g. qemu will know to find them.
> Note: we added a new structure as opposed to extending existing one
> because someone might be relying on the size of the existing structure
> staying unchanged.  Add a warning to avoid using sizeof.
>
> Signed-off-by: Michael S. Tsirkin <mst@...hat.com>

Acked-by: Jason Wang <jasowang@...hat.com>

Thanks

> ---
>  drivers/virtio/virtio_pci_modern_dev.c |  7 ++++---
>  include/linux/virtio_pci_modern.h      |  7 -------
>  include/uapi/linux/virtio_pci.h        | 11 +++++++++++
>  3 files changed, 15 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/virtio/virtio_pci_modern_dev.c b/drivers/virtio/virtio_pci_modern_dev.c
> index e2a1fe7bb66c..7de8b1ebabac 100644
> --- a/drivers/virtio/virtio_pci_modern_dev.c
> +++ b/drivers/virtio/virtio_pci_modern_dev.c
> @@ -294,9 +294,10 @@ int vp_modern_probe(struct virtio_pci_modern_device *mdev)
>
>         err = -EINVAL;
>         mdev->common = vp_modern_map_capability(mdev, common,
> -                                     sizeof(struct virtio_pci_common_cfg), 4,
> -                                     0, sizeof(struct virtio_pci_modern_common_cfg),
> -                                     &mdev->common_len, NULL);
> +                             sizeof(struct virtio_pci_common_cfg), 4, 0,
> +                             offsetofend(struct virtio_pci_modern_common_cfg,
> +                                         queue_reset),
> +                             &mdev->common_len, NULL);
>         if (!mdev->common)
>                 goto err_map_common;
>         mdev->isr = vp_modern_map_capability(mdev, isr, sizeof(u8), 1,
> diff --git a/include/linux/virtio_pci_modern.h b/include/linux/virtio_pci_modern.h
> index d0f2797420f7..a09e13a577a9 100644
> --- a/include/linux/virtio_pci_modern.h
> +++ b/include/linux/virtio_pci_modern.h
> @@ -5,13 +5,6 @@
>  #include <linux/pci.h>
>  #include <linux/virtio_pci.h>
>
> -struct virtio_pci_modern_common_cfg {
> -       struct virtio_pci_common_cfg cfg;
> -
> -       __le16 queue_notify_data;       /* read-write */
> -       __le16 queue_reset;             /* read-write */
> -};
> -
>  /**
>   * struct virtio_pci_modern_device - info for modern PCI virtio
>   * @pci_dev:       Ptr to the PCI device struct
> diff --git a/include/uapi/linux/virtio_pci.h b/include/uapi/linux/virtio_pci.h
> index f703afc7ad31..44f4dd2add18 100644
> --- a/include/uapi/linux/virtio_pci.h
> +++ b/include/uapi/linux/virtio_pci.h
> @@ -166,6 +166,17 @@ struct virtio_pci_common_cfg {
>         __le32 queue_used_hi;           /* read-write */
>  };
>
> +/*
> + * Warning: do not use sizeof on this: use offsetofend for
> + * specific fields you need.
> + */
> +struct virtio_pci_modern_common_cfg {
> +       struct virtio_pci_common_cfg cfg;
> +
> +       __le16 queue_notify_data;       /* read-write */
> +       __le16 queue_reset;             /* read-write */
> +};
> +
>  /* Fields in VIRTIO_PCI_CAP_PCI_CFG: */
>  struct virtio_pci_cfg_cap {
>         struct virtio_pci_cap cap;
> --
> MST
>