Re: [PATCH V2 6/8] mdev: introduce virtio device and its device ops

Jason Wang
2019-09-25T12:45:21Z

On 2019/9/25 下午5:09, Tian, Kevin wrote:
>> From: Jason Wang [mailto:jasowang@redhat.com]
>> Sent: Tuesday, September 24, 2019 9:54 PM
>>
>> This patch implements basic support for mdev driver that supports
>> virtio transport for kernel virtio driver.
>>
>> Signed-off-by: Jason Wang <jasowang@redhat.com>
>> ---
>> include/linux/mdev.h | 2 +
>> include/linux/virtio_mdev.h | 145
>> ++++++++++++++++++++++++++++++++++++
>> 2 files changed, 147 insertions(+)
>> create mode 100644 include/linux/virtio_mdev.h
>>
>> diff --git a/include/linux/mdev.h b/include/linux/mdev.h
>> index 3414307311f1..73ac27b3b868 100644
>> --- a/include/linux/mdev.h
>> +++ b/include/linux/mdev.h
>> @@ -126,6 +126,8 @@ struct mdev_device *mdev_from_dev(struct device
>> *dev);
>>
>> enum {
>> MDEV_ID_VFIO = 1,
>> + MDEV_ID_VIRTIO = 2,
>> + MDEV_ID_VHOST = 3,
>> /* New entries must be added here */
>> };
>>
>> diff --git a/include/linux/virtio_mdev.h b/include/linux/virtio_mdev.h
>> new file mode 100644
>> index 000000000000..d1a40a739266
>> --- /dev/null
>> +++ b/include/linux/virtio_mdev.h
>> @@ -0,0 +1,145 @@
>> +/* SPDX-License-Identifier: GPL-2.0-only */
>> +/*
>> + * Virtio mediated device driver
>> + *
>> + * Copyright 2019, Red Hat Corp.
>> + * Author: Jason Wang <jasowang@redhat.com>
>> + */
>> +#ifndef _LINUX_VIRTIO_MDEV_H
>> +#define _LINUX_VIRTIO_MDEV_H
>> +
>> +#include <linux/interrupt.h>
>> +#include <linux/mdev.h>
>> +#include <uapi/linux/vhost.h>
>> +
>> +#define VIRTIO_MDEV_DEVICE_API_STRING "virtio-mdev"
>> +#define VIRTIO_MDEV_VERSION 0x1
> Just be curious. is this version identical to virtio spec version that below
> callbacks are created for, or just irrelevant?

It could be a hint but basically it's a way for userspace driver
compatibility. For kernel we don't need this.

>
>> +
>> +struct virtio_mdev_callback {
>> + irqreturn_t (*callback)(void *data);
>> + void *private;
>> +};
>> +
>> +/**
>> + * struct vfio_mdev_device_ops - Structure to be registered for each
>> + * mdev device to register the device to virtio-mdev module.
>> + *
>> + * @set_vq_address: Set the address of virtqueue
>> + * @mdev: mediated device
>> + * @idx: virtqueue index
>> + * @desc_area: address of desc area
>> + * @driver_area: address of driver area
>> + * @device_area: address of device area
>> + * Returns integer: success (0) or error (< 0)
>> + * @set_vq_num: Set the size of virtqueue
>> + * @mdev: mediated device
>> + * @idx: virtqueue index
>> + * @num: the size of virtqueue
>> + * @kick_vq: Kick the virtqueue
>> + * @mdev: mediated device
>> + * @idx: virtqueue index
>> + * @set_vq_cb: Set the interrut calback function for
>> + * a virtqueue
>> + * @mdev: mediated device
>> + * @idx: virtqueue index
>> + * @cb: virtio-mdev interrupt callback
>> structure
>> + * @set_vq_ready: Set ready status for a virtqueue
>> + * @mdev: mediated device
>> + * @idx: virtqueue index
>> + * @ready: ready (true) not ready(false)
>> + * @get_vq_ready: Get ready status for a virtqueue
>> + * @mdev: mediated device
>> + * @idx: virtqueue index
>> + * Returns boolean: ready (true) or not (false)
>> + * @set_vq_state: Set the state for a virtqueue
>> + * @mdev: mediated device
>> + * @idx: virtqueue index
>> + * @state: virtqueue state (last_avail_idx)
>> + * Returns integer: success (0) or error (< 0)
>> + * @get_vq_state: Get the state for a virtqueue
>> + * @mdev: mediated device
>> + * @idx: virtqueue index
>> + * Returns virtqueue state (last_avail_idx)
>> + * @get_vq_align: Get the virtqueue align requirement
>> + * for the device
>> + * @mdev: mediated device
>> + * Returns virtqueue algin requirement
>> + * @get_features: Get virtio features supported by the device
>> + * @mdev: mediated device
>> + * Returns the features support by the
>> + * device
>> + * @get_features: Set virtio features supported by the driver
>> + * @mdev: mediated device
>> + * @features: feature support by the driver
>> + * Returns integer: success (0) or error (< 0)
>> + * @set_config_cb: Set the config interrupt callback
>> + * @mdev: mediated device
>> + * @cb: virtio-mdev interrupt callback
>> structure
>> + * @get_device_id: Get virtio device id
>> + * @mdev: mediated device
>> + * Returns u32: virtio device id
>> + * @get_vendor_id: Get virtio vendor id
>> + * @mdev: mediated device
>> + * Returns u32: virtio vendor id
>> + * @get_status: Get the device status
>> + * @mdev: mediated device
>> + * Returns u8: virtio device status
>> + * @set_status: Set the device status
>> + * @mdev: mediated device
>> + * @status: virtio device status
>> + * @get_config: Read from device specific confiugration
>> space
> configuration (and similar typos downward)

Let me fix.

>
>> + * @mdev: mediated device
>> + * @offset: offset from the beginning of
>> + * configuration space
>> + * @buf: buffer used to read to
>> + * @len: the length to read from
>> + * configration space
>> + * @set_config: Write to device specific confiugration space
>> + * @mdev: mediated device
>> + * @offset: offset from the beginning of
>> + * configuration space
>> + * @buf: buffer used to write from
>> + * @len: the length to write to
>> + * configration space
>> + * @get_version: Get the version of virtio mdev device
>> + * @mdev: mediated device
>> + * Returns integer: version of the device
>> + * @get_generation: Get device generaton
>> + * @mdev: mediated device
>> + * Returns u32: device generation
>> + */
>> +struct virtio_mdev_device_ops {
>> + /* Virtqueue ops */
>> + int (*set_vq_address)(struct mdev_device *mdev,
>> + u16 idx, u64 desc_area, u64 driver_area,
>> + u64 device_area);
>> + void (*set_vq_num)(struct mdev_device *mdev, u16 idx, u32 num);
>> + void (*kick_vq)(struct mdev_device *mdev, u16 idx);
>> + void (*set_vq_cb)(struct mdev_device *mdev, u16 idx,
>> + struct virtio_mdev_callback *cb);
>> + void (*set_vq_ready)(struct mdev_device *mdev, u16 idx, bool
>> ready);
>> + bool (*get_vq_ready)(struct mdev_device *mdev, u16 idx);
>> + int (*set_vq_state)(struct mdev_device *mdev, u16 idx, u64 state);
>> + u64 (*get_vq_state)(struct mdev_device *mdev, u16 idx);
>> +
>> + /* Device ops */
>> + u16 (*get_vq_align)(struct mdev_device *mdev);
>> + u64 (*get_features)(struct mdev_device *mdev);
>> + int (*set_features)(struct mdev_device *mdev, u64 features);
>> + void (*set_config_cb)(struct mdev_device *mdev,
>> + struct virtio_mdev_callback *cb);
>> + u16 (*get_queue_max)(struct mdev_device *mdev);
>> + u32 (*get_device_id)(struct mdev_device *mdev);
>> + u32 (*get_vendor_id)(struct mdev_device *mdev);
>> + u8 (*get_status)(struct mdev_device *mdev);
>> + void (*set_status)(struct mdev_device *mdev, u8 status);
>> + void (*get_config)(struct mdev_device *mdev, unsigned int offset,
>> + void *buf, unsigned int len);
>> + void (*set_config)(struct mdev_device *mdev, unsigned int offset,
>> + const void *buf, unsigned int len);
>> + int (*get_version)(struct mdev_device *mdev);
>> + u32 (*get_generation)(struct mdev_device *mdev);
>> +};
> I'm not sure how stable above ops are.

It's the kernel internal API, so there's no strict requirement for this.
We will export a version value for userspace for compatibility.

> Does it make sense if defining
> just two callbacks here, e.g. vq_ctrl and device_ctrl, and then let the
> vendor driver to handle specific ops in each category (similar to how
> ioctl works)?

My understanding is that it introduce another indirection, you still
need to differ from different command, and it's less flexible than
direct callback.

What's the value of doing this?

Thanks

>
> Thanks
> Kevin
>