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Date:   Tue, 14 Sep 2021 08:58:28 -0400
From:   "Michael S. Tsirkin" <mst@redhat.com>
To:     Wu Zongyong <wuzongyong@linux.alibaba.com>
Cc:     jasowang@redhat.com, virtualization@lists.linux-foundation.org,
        linux-kernel@vger.kernel.org, wei.yang1@linux.alibaba.com
Subject: Re: [PATCH v2 4/5] vdpa: add new vdpa attribute
 VDPA_ATTR_DEV_F_VERSION_1
Message-ID: <20210914085711-mutt-send-email-mst@kernel.org>
References: <cover.1631101392.git.wuzongyong@linux.alibaba.com>
 <cover.1631621507.git.wuzongyong@linux.alibaba.com>
 <834528d24c839080215b2e077f100e9ed5073edc.1631621507.git.wuzongyong@linux.alibaba.com>
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In-Reply-To: <834528d24c839080215b2e077f100e9ed5073edc.1631621507.git.wuzongyong@linux.alibaba.com>
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On Tue, Sep 14, 2021 at 08:24:51PM +0800, Wu Zongyong wrote:
> This new attribute advertises whether the vdpa device is legacy or not.
> Users can pick right virtqueue size if the vdpa device is legacy which
> doesn't support to change virtqueue size.
> 
> Signed-off-by: Wu Zongyong <wuzongyong@linux.alibaba.com>

So if we are bothering with legacy, I think there are
several things to do when building the interface
- support transitional devices, that is allow userspace
  to tell device it's in legacy mode
- support reporting/setting supporting endian-ness

> ---
>  drivers/vdpa/vdpa.c          | 6 ++++++
>  drivers/virtio/virtio_vdpa.c | 7 ++++++-
>  include/uapi/linux/vdpa.h    | 1 +
>  3 files changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/vdpa/vdpa.c b/drivers/vdpa/vdpa.c
> index 1dc121a07a93..533d7f589eee 100644
> --- a/drivers/vdpa/vdpa.c
> +++ b/drivers/vdpa/vdpa.c
> @@ -12,6 +12,7 @@
>  #include <linux/slab.h>
>  #include <linux/vdpa.h>
>  #include <uapi/linux/vdpa.h>
> +#include <uapi/linux/virtio_config.h>
>  #include <net/genetlink.h>
>  #include <linux/mod_devicetable.h>
>  
> @@ -494,6 +495,7 @@ vdpa_dev_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid, u32 seq
>  	u16 max_vq_size;
>  	u32 device_id;
>  	u32 vendor_id;
> +	u64 features;
>  	void *hdr;
>  	int err;
>  
> @@ -508,6 +510,7 @@ vdpa_dev_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid, u32 seq
>  	device_id = vdev->config->get_device_id(vdev);
>  	vendor_id = vdev->config->get_vendor_id(vdev);
>  	max_vq_size = vdev->config->get_vq_num_max(vdev);
> +	features = vdev->config->get_features(vdev);
>  
>  	err = -EMSGSIZE;
>  	if (nla_put_string(msg, VDPA_ATTR_DEV_NAME, dev_name(&vdev->dev)))
> @@ -520,6 +523,9 @@ vdpa_dev_fill(struct vdpa_device *vdev, struct sk_buff *msg, u32 portid, u32 seq
>  		goto msg_err;
>  	if (nla_put_u16(msg, VDPA_ATTR_DEV_MAX_VQ_SIZE, max_vq_size))
>  		goto msg_err;
> +	if (features & BIT_ULL(VIRTIO_F_VERSION_1) &&
> +	    nla_put_flag(msg, VDPA_ATTR_DEV_VERSION_1))
> +		goto msg_err;
>  
>  	genlmsg_end(msg, hdr);
>  	return 0;
> diff --git a/drivers/virtio/virtio_vdpa.c b/drivers/virtio/virtio_vdpa.c
> index 72eaef2caeb1..1cba957c4cdc 100644
> --- a/drivers/virtio/virtio_vdpa.c
> +++ b/drivers/virtio/virtio_vdpa.c
> @@ -7,6 +7,7 @@
>   *
>   */
>  
> +#include "linux/virtio_config.h"
>  #include <linux/init.h>
>  #include <linux/module.h>
>  #include <linux/device.h>
> @@ -145,6 +146,7 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
>  	/* Assume split virtqueue, switch to packed if necessary */
>  	struct vdpa_vq_state state = {0};
>  	unsigned long flags;
> +	bool may_reduce_num = false;
>  	u32 align, num;
>  	int err;
>  
> @@ -169,10 +171,13 @@ virtio_vdpa_setup_vq(struct virtio_device *vdev, unsigned int index,
>  		goto error_new_virtqueue;
>  	}
>  
> +	if (ops->get_features(vdpa) & BIT_ULL(VIRTIO_F_VERSION_1))
> +		may_reduce_num = true;
> +
>  	/* Create the vring */
>  	align = ops->get_vq_align(vdpa);
>  	vq = vring_create_virtqueue(index, num, align, vdev,
> -				    true, true, ctx,
> +				    true, may_reduce_num, ctx,
>  				    virtio_vdpa_notify, callback, name);
>  	if (!vq) {
>  		err = -ENOMEM;
> diff --git a/include/uapi/linux/vdpa.h b/include/uapi/linux/vdpa.h
> index 66a41e4ec163..ce0b74276a5b 100644
> --- a/include/uapi/linux/vdpa.h
> +++ b/include/uapi/linux/vdpa.h
> @@ -32,6 +32,7 @@ enum vdpa_attr {
>  	VDPA_ATTR_DEV_VENDOR_ID,		/* u32 */
>  	VDPA_ATTR_DEV_MAX_VQS,			/* u32 */
>  	VDPA_ATTR_DEV_MAX_VQ_SIZE,		/* u16 */
> +	VDPA_ATTR_DEV_VERSION_1,		/* flag */
>  
>  	/* new attributes must be added above here */
>  	VDPA_ATTR_MAX,
> -- 
> 2.31.1