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

["Michael S. Tsirkin" <mst@redhat.com>]

On Wed, Sep 25, 2019 at 08:45:21PM +0800, Jason Wang wrote:
> 
> 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.

Given it's tied to virtio we probably want kernel+userspace
feature bits?

> 
> > 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
> > 
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