Re: [PATCH v3 2/2] rust: workqueue: add creation of workqueues

[Danilo Krummrich]

On Fri Feb 27, 2026 at 8:05 PM CET, Alice Ryhl wrote:
> On Fri, Feb 27, 2026 at 04:30:59PM +0100, Danilo Krummrich wrote:
>> On Fri Feb 27, 2026 at 3:53 PM CET, Alice Ryhl wrote:
>> > +    /// Set the maximum number of active cpus.
>> > +    ///
>> > +    /// If not set, a reasonable default value is used. The maximum value is `WQ_MAX_ACTIVE`.
>> 
>> Should we just mention the default value?
>
> I can mention the constant name, but I'd like to avoid mentioning a
> value that might change.

Yes, that's what I meant.

>> > +    #[inline]
>> > +    pub fn max_active(mut self, max_active: u32) -> Builder {
>> > +        self.max_active = i32::try_from(max_active).unwrap_or(i32::MAX);
>> 
>> The workqueue code prints a warning for max_active >  WQ_MAX_ACTIVE. Maybe use
>> debug_assert()?
>
> What's wrong with just making use of the C-side warning?

IIRC, we have the same pattern in other Rust code that we use debug_assert()
when a value got clamped, e.g. in udelay().

>> It's also a bit unfortunate that alloc_ordered_workqueue() becomes
>> .max_active(1).
>> 
>> At the same time having a separate ordered() method competes with max_active().
>> 
>> Mybe a type state, i.e. Builder<Ordered> that doesn't have max_active()?
>
> Sorry I'm a bit confused by this. Why does an ordered() compete with
> max_active()?

Because you could get an inconsistent state with __WQ_ORDERED and
max_active > 1.

It also conflicts with sysfs() I think [1].

[1] https://elixir.bootlin.com/linux/v6.19.3/source/kernel/workqueue.c#L7417