[Xen-devel] Re: [kvm-devel] [PATCH RFC 1/3] virtio infrastructure

[Avi Kivity <avi@xxxxxxxxxxxx>]

Rusty Russell wrote:
> This attempts to implement a "virtual I/O" layer which should allow
> common drivers to be efficiently used across most virtual I/O
> mechanisms.  It will no-doubt need further enhancement.
>
> The details of probing the device are left to hypervisor-specific
> code: it simple constructs the "struct virtio_device" and hands it to
> the probe function (eg. virtnet_probe() or virtblk_probe()).
>
> The virtio drivers add and detach input and output buffers; as the
> buffers are used up their associated "used" pointers are filled in.
>
>   

Good stuff.

> +/**
> + * virtio_ops - virtio abstraction layer
> + * @add_outbuf: prepare to send data to the other end:
> + *   vdev: the virtio_device
> + *   sg: the description of the buffer(s).
> + *   num: the size of the sg array.
> + *   used: the length sent (set once sending is done).
> + *      Returns an identifier or an error.
> + * @add_inbuf: prepare to receive data from the other end:
> + *   vdev: the virtio_device
> + *   sg: the description of the buffer(s).
> + *   num: the size of the sg array.
> + *   used: the length sent (set once data received).
> + *      Returns an identifier or an error (eg. -ENOSPC).
>   

Instead of 'used', how about a completion callback (with associated data
pointer)?  A new helper, virtio_complete(), would call the callback for
all completed requests.  It would eliminate all the tedious scanning
used to match the identifier.

It would also be nice to support a bit of non-buffer data, like a set of
bitflags.


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to 
panic.


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