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Re: Why QEMU should move from C to Rust (clickbait alert ;))

From: Daniel P . Berrangé
Subject: Re: Why QEMU should move from C to Rust (clickbait alert ;))
Date: Thu, 6 Aug 2020 13:01:30 +0100
User-agent: Mutt/1.14.5 (2020-06-23)

On Thu, Aug 06, 2020 at 01:51:48PM +0200, Sergio Lopez wrote:
> On Thu, Aug 06, 2020 at 11:24:13AM +0100, Stefan Hajnoczi wrote:
> <snip>
> > Conclusion
> > ---------------
> > Most security bugs in QEMU today are C programming bugs. Switching to
> > a safer programming language will significantly reduce security bugs
> > in QEMU. Rust is now mature and proven enough to use as the language
> > for device emulation code. Thanks to vhost-user and vfio-user using
> > Rust for device emulation does not require a big conversion of QEMU
> > code, it can simply be done in a separate program. This way attack
> > surfaces can be written in Rust to make them less susceptible to
> > security bugs going forward.
> > 
> Having worked on Rust implementations for vhost-user-fs and
> vhost-user-blk, I'm 100% sold on this idea.
> That said, there are a couple things that I think may help getting
> more people into implementing vhost-user devices in Rust.
>  1. Having a reference implementation for a simple device somewhere
>  close or inside the QEMU source tree. I'd say vhost-user-blk is a
>  clear candidate, given that a naive implementation for raw files
>  without any I/O optimization is quite easy to read and understand.
>  2. Integrating the ability to start-up vhost-user daemons from QEMU,
>  in an easy and portable way. I know we can always rely on daemons
>  like libvirt to do this for us, but I think it'd be nicer to be able
>  to define a vhost-user device from the command line and have QEMU
>  execute it with the proper parameters (BTW, Cloud-Hypervisor already
>  does that). This would probably require some kind of configuration
>  file, to be able to define which binary provides each vhost-user
>  device personality, but could also be a way for "sanctioning"
>  daemons (through the configuration defaults), and to have them adhere
>  to a standardized command line format.

This second point is such a good idea that we already have defined
how todo this in QEMU - see the docs/interop/vhost-user.json file.
This specifies metadata files that should be installed into a
defined location such that QEMU/libvirt/other mgmt app can locate
vhost-user impls for each type of device, and priortize between
different impls.

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