[RFC] bhyve: modeling virtio-9p

[Daniel P. Berrangé]

On Tue, Oct 06, 2020 at 06:51:52PM +0400, Roman Bogorodskiy wrote:
> Hi,
> 
> Recently bhyve got virtio-9p support. Modeling it appears to be pretty
> straight-forward, but probably I'm missing something, so decided to
> discuss first before proceeding with the implementation.
> 
> On the host side it looks like this:
> 
>   bhyve .... -s 25:0,virtio-9p,distfiles=/workspace/distfiles
> 
> Mounting it in a (Linux) guest looks this way:
> 
>   mount -t 9p distfiles /mnt/distfiles
> 
> lspci(8) shows it like this:
> 
> 00:1f.0 SCSI storage controller: Red Hat, Inc. Virtio filesystem
>         Subsystem: Red Hat, Inc. Virtio filesystem
>         Flags: bus master, fast devsel, latency 64, IRQ 20
>         I/O ports at 2200 [size=512]
>         Memory at c2004000 (32-bit, non-prefetchable) [size=8K]
>         Expansion ROM at c0007000 [virtual] [disabled] [size=2K]
>         Capabilities: [40] MSI-X: Enable+ Count=2 Masked-
>         Capabilities: [4c] MSI: Enable- Count=1/1 Maskable- 64bit+
>         Kernel driver in use: virtio-pci
> 
> I was thinking about presenting it like this:
> 
>   <filesystem type='mount'>
>     <driver type='virtiofs'/>

This driver type is for virtio-fuse, which is different from virtio-9p.
In QEMU we support type=path and type=handle as two different QEMU
bakends for 9p. Or simply omit  "type" entirely and it defaults to
9p in QEMU. So I think you can just omit "type" for bhyve too.

>     <source dir='/workspace/distfiles'>
>     <target dir='distfiles'/>
>   </filesystem>
> 
> There's also an optional <readonly/> element for readonly mounts, which
> is also supported by bhyve.

Yep.

Also consider the "accessmode" attribute - you'll want to validate
whichever value(s) of that make sense given the bhyve impl of 9p.

Regards,
Daniel
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