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SubjectRe: [RFC PATCH 3/4] virtio: introudce a mdev based transport
On Wed, Sep 11, 2019 at 10:38:39AM +0800, Jason Wang wrote:
>
> On 2019/9/10 下午9:52, Michael S. Tsirkin wrote:
> > On Tue, Sep 10, 2019 at 09:13:02PM +0800, Jason Wang wrote:
> > > 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?
> > Should we just reuse VIRTIO_PCI_COMMON_Q_XXX then?
>
>
> You mean something like VIRTIO_PCI_COMMON_Q_MSIX? Then it becomes a PCI
> transport in fact. And using either MSIX or irq number is actually another
> layer of indirection. So I think we can just write callback function and
> parameter through registers.

I just realized, all these registers are just encoded so you
can pass stuff through read/write. But it can instead be
just a normal C function call with no messy encoding.
So why do we want to do this encoding?


>
> >
> >
> > > > > +
> > > > > +#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"?
> > I really meant "enabled", didn't remember the correct name.
> > As in: VIRTIO_PCI_COMMON_Q_ENABLE
>
>
> Yes, it's the same.
>
> Thanks
>
>
> >
> > > > > +
> > > > > +/* 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

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