netdev - Re: [RFC PATCH 3/4] virtio: introudce a mdev based transport

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Message-ID: <572ffc34-3081-8503-d3cc-192edc9b5311@redhat.com>
Date:   Tue, 10 Sep 2019 21:13:02 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     kvm@...r.kernel.org, virtualization@...ts.linux-foundation.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        kwankhede@...dia.com, alex.williamson@...hat.com,
        cohuck@...hat.com, tiwei.bie@...el.com, maxime.coquelin@...hat.com,
        cunming.liang@...el.com, zhihong.wang@...el.com,
        rob.miller@...adcom.com, idos@...lanox.com, xiao.w.wang@...el.com,
        haotian.wang@...ive.com
Subject: Re: [RFC PATCH 3/4] virtio: introudce a mdev based transport


On 2019/9/10 下午6:01, Michael S. Tsirkin wrote:
>> +#ifndef _LINUX_VIRTIO_MDEV_H
>> +#define _LINUX_VIRTIO_MDEV_H
>> +
>> +#include <linux/interrupt.h>
>> +#include <linux/vringh.h>
>> +#include <uapi/linux/virtio_net.h>
>> +
>> +/*
>> + * Ioctls
>> + */
> Pls add a bit more content here. It's redundant to state these
> are ioctls. Much better to document what does each one do.


Ok.


>
>> +
>> +struct virtio_mdev_callback {
>> +	irqreturn_t (*callback)(void *);
>> +	void *private;
>> +};
>> +
>> +#define VIRTIO_MDEV 0xAF
>> +#define VIRTIO_MDEV_SET_VQ_CALLBACK _IOW(VIRTIO_MDEV, 0x00, \
>> +					 struct virtio_mdev_callback)
>> +#define VIRTIO_MDEV_SET_CONFIG_CALLBACK _IOW(VIRTIO_MDEV, 0x01, \
>> +					struct virtio_mdev_callback)
> Function pointer in an ioctl parameter? How does this ever make sense?


I admit this is hacky (casting).


> And can't we use a couple of registers for this, and avoid ioctls?


Yes, how about something like interrupt numbers for each virtqueue and 
config?


>
>> +
>> +#define VIRTIO_MDEV_DEVICE_API_STRING		"virtio-mdev"
>> +
>> +/*
>> + * Control registers
>> + */
>> +
>> +/* Magic value ("virt" string) - Read Only */
>> +#define VIRTIO_MDEV_MAGIC_VALUE		0x000
>> +
>> +/* Virtio device version - Read Only */
>> +#define VIRTIO_MDEV_VERSION		0x004
>> +
>> +/* Virtio device ID - Read Only */
>> +#define VIRTIO_MDEV_DEVICE_ID		0x008
>> +
>> +/* Virtio vendor ID - Read Only */
>> +#define VIRTIO_MDEV_VENDOR_ID		0x00c
>> +
>> +/* Bitmask of the features supported by the device (host)
>> + * (32 bits per set) - Read Only */
>> +#define VIRTIO_MDEV_DEVICE_FEATURES	0x010
>> +
>> +/* Device (host) features set selector - Write Only */
>> +#define VIRTIO_MDEV_DEVICE_FEATURES_SEL	0x014
>> +
>> +/* Bitmask of features activated by the driver (guest)
>> + * (32 bits per set) - Write Only */
>> +#define VIRTIO_MDEV_DRIVER_FEATURES	0x020
>> +
>> +/* Activated features set selector - Write Only */
>> +#define VIRTIO_MDEV_DRIVER_FEATURES_SEL	0x024
>> +
>> +/* Queue selector - Write Only */
>> +#define VIRTIO_MDEV_QUEUE_SEL		0x030
>> +
>> +/* Maximum size of the currently selected queue - Read Only */
>> +#define VIRTIO_MDEV_QUEUE_NUM_MAX	0x034
>> +
>> +/* Queue size for the currently selected queue - Write Only */
>> +#define VIRTIO_MDEV_QUEUE_NUM		0x038
>> +
>> +/* Ready bit for the currently selected queue - Read Write */
>> +#define VIRTIO_MDEV_QUEUE_READY		0x044
> Is this same as started?


Do you mean "status"?


>
>> +
>> +/* Alignment of virtqueue - Read Only */
>> +#define VIRTIO_MDEV_QUEUE_ALIGN		0x048
>> +
>> +/* Queue notifier - Write Only */
>> +#define VIRTIO_MDEV_QUEUE_NOTIFY	0x050
>> +
>> +/* Device status register - Read Write */
>> +#define VIRTIO_MDEV_STATUS		0x060
>> +
>> +/* Selected queue's Descriptor Table address, 64 bits in two halves */
>> +#define VIRTIO_MDEV_QUEUE_DESC_LOW	0x080
>> +#define VIRTIO_MDEV_QUEUE_DESC_HIGH	0x084
>> +
>> +/* Selected queue's Available Ring address, 64 bits in two halves */
>> +#define VIRTIO_MDEV_QUEUE_AVAIL_LOW	0x090
>> +#define VIRTIO_MDEV_QUEUE_AVAIL_HIGH	0x094
>> +
>> +/* Selected queue's Used Ring address, 64 bits in two halves */
>> +#define VIRTIO_MDEV_QUEUE_USED_LOW	0x0a0
>> +#define VIRTIO_MDEV_QUEUE_USED_HIGH	0x0a4
>> +
>> +/* Configuration atomicity value */
>> +#define VIRTIO_MDEV_CONFIG_GENERATION	0x0fc
>> +
>> +/* The config space is defined by each driver as
>> + * the per-driver configuration space - Read Write */
>> +#define VIRTIO_MDEV_CONFIG		0x100
> Mixing device and generic config space is what virtio pci did,
> caused lots of problems with extensions.
> It would be better to reserve much more space.


I see, will do this.

Thanks


>
>
>> +
>> +#endif
>> +
>> +
>> +/* Ready bit for the currently selected queue - Read Write */
>> -- 
>> 2.19.1