Re: [pbs-devel] applied: [PATCH proxmox-backup] fix: proxmox-backup-manager network reload wait on worker

[Wolfgang Bumiller <w.bumiller@proxmox.com>]

On Fri, Aug 30, 2024 at 10:18:22AM GMT, Gabriel Goller wrote:
> On 29.08.2024 14:17, Wolfgang Bumiller wrote:
> > applied, thanks
> > 
> > On Wed, Aug 21, 2024 at 12:22:36PM GMT, Gabriel Goller wrote:
> > > Make the `network reload` command in proxmox-backup-manager wait on the
> > > api handler's workertask. Otherwise the task would be killed when the
> > > client exits.
> > > 
> > > Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
> > > ---
> > >  src/bin/proxmox_backup_manager/network.rs | 21 +++++++++++++++++++--
> > >  1 file changed, 19 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/src/bin/proxmox_backup_manager/network.rs b/src/bin/proxmox_backup_manager/network.rs
> > > index deac5b1b2960..0f0a50a8932a 100644
> > > --- a/src/bin/proxmox_backup_manager/network.rs
> > > +++ b/src/bin/proxmox_backup_manager/network.rs
> > > @@ -129,6 +129,24 @@ fn pending_network_changes(
> > >      Ok(Value::Null)
> > >  }
> > > 
> > > +#[api()]
> > > +/// Reload network changes
> > > +async fn reload_network_changes(
> > > +    mut param: Value,
> > > +    rpcenv: &mut dyn RpcEnvironment,
> > > +) -> Result<Value, Error> {
> > > +    param["node"] = "localhost".into();
> > > +
> > > +    let info = &api2::node::network::API_METHOD_RELOAD_NETWORK_CONFIG;
> > > +    let result = match info.handler {
> > > +        ApiHandler::Async(handler) => (handler)(param, info, rpcenv).await?,
> > > +        _ => unreachable!(),
> > > +    };
> > 
> > Note: we have the above pattern a lot. For `Schema` we already have a
> > bunch of `const fn unwrap_<type>_schema()`.
> > We can now also use `const {}` expressions, so maybe we should have
> > something like this for `ApiHandler` as well, with all these handler
> > functions then using something like:
> > 
> >    let handler = const { info.handler.unwrap_async_handler() };
> >    let result = (handler)(param, info, rpcenv).await?
> > 
> 
> Hmm on a second glance, I don't think we can do this currently.
> 
> I tried this:
> 
>     pub const fn unwrap_async_handler(&self) -> &ApiAsyncHandlerFn {
>         match self {
>             ApiHandler::Async(a) => a,
>             _ => panic!("unwrap_async_handler called on wrong apihandler"),
>         }
>     }
> 
> But it doesn't compile because we have a &mut reference in
> `ApiAsyncHandlerFn` and mutable references in `const fn`'s currently
> don't work [0].
> 
> Obviously we can make everything non-const and still improve the
> readability.
> 
> [0]: https://github.com/rust-lang/rust/issues/57349.

This looks like a bug, actually. The linked issue is about mutable
references used inside the functions, however, this mutable references
is actually part of a function signature in the *output*.
This has been addressed for *regular* function pointers here[0], but
apparently not for Fn traits.

[0] https://github.com/rust-lang/rust/pull/116015


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