Re: [PATCH 07/24] DAX: virtio-fs: Add vhost-user slave commands for mapping

[Stefan Hajnoczi]

On Tue, Feb 09, 2021 at 07:02:07PM +0000, Dr. David Alan Gilbert (git) wrote:
> diff --git a/docs/interop/vhost-user.rst b/docs/interop/vhost-user.rst
> index d6085f7045..1deedd3407 100644
> --- a/docs/interop/vhost-user.rst
> +++ b/docs/interop/vhost-user.rst
> @@ -1432,6 +1432,26 @@ Slave message types
>  
>    The state.num field is currently reserved and must be set to 0.
>  
> +``VHOST_USER_SLAVE_FS_MAP``
> +  :id: 6
> +  :equivalent ioctl: N/A
> +  :slave payload: fd + n * (offset + address + len)

I'm not sure I understand this notation. '+' means field concatenation?
Is 'fd' a field or does it indicate file descriptor passing?

I suggest using a struct name instead of informal notation so that the
payload size and representation is clear.

The same applies for VHOST_USER_SLAVE_FS_UNMAP.

> +  :master payload: N/A
> +
> +  Requests that the QEMU mmap the given fd into the virtio-fs cache;

s/QEMU mmap the given fd/given fd be mmapped/

Please avoid mentioning QEMU specifically. Any VMM should be able to
implement this spec.

The same applies for VHOST_USER_SLAVE_FS_UNMAP.

> +  multiple chunks can be mapped in one command.
> +  A reply is generated indicating whether mapping succeeded.
> +
> +``VHOST_USER_SLAVE_FS_UNMAP``
> +  :id: 7
> +  :equivalent ioctl: N/A
> +  :slave payload: n * (address + len)
> +  :master payload: N/A
> +
> +  Requests that the QEMU un-mmap the given range in the virtio-fs cache;
> +  multiple chunks can be unmapped in one command.
> +  A reply is generated indicating whether unmapping succeeded.

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