Re: [PATCH RFC 0/5] rust: implement tracing

[Manos Pitsidianakis <manos.pitsidianakis@linaro.org>]

On Tue, Aug 5, 2025 at 7:43 PM Daniel P. Berrangé <berrange@redhat.com> wrote:
>
> On Tue, Aug 05, 2025 at 07:25:39PM +0300, Manos Pitsidianakis wrote:
> > On Tue, Aug 5, 2025 at 7:05 PM Daniel P. Berrangé <berrange@redhat.com> wrote:
> > >
> > > On Mon, Aug 04, 2025 at 04:47:13PM +0300, Manos Pitsidianakis wrote:
> > > > This RFC series contains some simple patches I've been sitting on for
> > > > some months to allow tracing in rust devices in a similar matter to C,
> > > > only it's done via a proc-macro codegen instead of using tracetool
> > > > script or equivalent.
> > >
> > > IIUC, this series is only emitting the traces events via the
> > > qemu_log function, and so feels like it is missing the benefit
> > > of tracing, vs the traditional logging framework.
> > >
> > > In our RHEL & Fedora distro builds we disable the log backend
> > > and enable dtrace, so that we have fully dynamic tracing and
> > > observability across the kernel, qemu, libvirt and other
> > > components with dtrace integration.
> >
> > Hi Daniel,
> >
> > Thanks for the insight! Do you have any points where I should look at
> > the trace implementation for how the different backends are supported?
> >
> > So I think there's already work in progress to support proper tracing
> > for Rust, I only sent this as a temporary fixup to provide some kind
> > of parity between C and Rust implementations until a proper, better
> > solution is available that can replace it.
>
> Can the rust code not easily consume the existing functions in the
> trace.h files generated for the C code as a short-term solution ?
>
> It would not benefit from the code inlining in the same way as C
> would, but it would at least give feature parity for tracing with
> all the trace backends are available.
>
> Then, we can look at optimizing with a pure rust impl of some
> backends at a later date, to regain what we lost from lack of
> inlining ?

It can, but we'd need to add extra intermediate steps to convert the
trace headers into Rust equivalent code, so it's not ideal.

I tried to generate code exactly like the generated trace headers
though, so I'm not sure what is missing to be honest (hence my
previous email question). The generated code generates TraceEvents and
registers them with trace_event_register_group. What else is missing
to support e.g. dtrace?

Thanks in advance,

-- 
Manos Pitsidianakis
Emulation and Virtualization Engineer at Linaro Ltd