linux-kernel - Re: [PATCH v5] rust: add global lock support

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Message-ID: <CAH5fLggv98iPAPm=PPa686osmfjqcdH9D3wD47ytCqkqbgwx7w@mail.gmail.com>
Date: Tue, 22 Oct 2024 19:24:38 +0200
From: Alice Ryhl <aliceryhl@...gle.com>
To: Boqun Feng <boqun.feng@...il.com>
Cc: Miguel Ojeda <ojeda@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>, Waiman Long <longman@...hat.com>, 
	Gary Guo <gary@...yguo.net>, Björn Roy Baron <bjorn3_gh@...tonmail.com>, 
	Benno Lossin <benno.lossin@...ton.me>, rust-for-linux@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Andreas Hindborg <a.hindborg@...nel.org>
Subject: Re: [PATCH v5] rust: add global lock support

On Tue, Oct 22, 2024 at 6:44 PM Boqun Feng <boqun.feng@...il.com> wrote:
>
> On Tue, Oct 22, 2024 at 02:46:19PM +0200, Alice Ryhl wrote:
> > On Mon, Oct 21, 2024 at 5:23 PM Boqun Feng <boqun.feng@...il.com> wrote:
> > >
> > > On Mon, Oct 21, 2024 at 01:17:23PM +0000, Alice Ryhl wrote:
> > > [...]
> > > > +///
> > > > +/// A global mutex used to protect all instances of a given struct.
> > > > +///
> > > > +/// ```
> > > > +/// # mod ex {
> > > > +/// # use kernel::prelude::*;
> > > > +/// kernel::sync::global_lock! {
> > > > +///     // SAFETY: Initialized in module initializer before first use.
> > > > +///     unsafe(uninit) static MY_MUTEX: Mutex<(), Guard = MyGuard, LockedBy = LockedByMyMutex> = ();
> > >
> > > Thanks! This looks much better now ;-)
> > >
> > > But I still want to get rid of "LockedBy=", so I've tried and seems it
> > > works, please see the below diff on top of your patch, I think it's
> > > better because:
> > >
> > > * Users don't to pick up the names for the locked_by type ;-)
> > > * It moves a significant amount of code out of macros.
> > > * By having:
> > >
> > >     struct MyStruct {
> > >         my_counter: GlobalLockedBy<MyGuard, u32>,
> > >     }
> > >
> > >   , it's much clear for users to see which guard is used to protected
> > >   `my_counter`.
> > >
> > > I prefer this way. Any concern about doing this?
> >
> > I think I came up with an even better way of doing it. The macro can
>
> Cool!
>
> > generate a dummy token type for the global lock, and then we can have
> > three types: GlobalLock<T>, GlobalGuard<T>, GlobalLockedBy<T> that are
> > all generic over the token type. The token type is an empty enum with
>
> Just to make sure I understand it, so let's say the token type's name is
> `TK`, you mean we have GlobalLock<T, TK>, GlobalGuard<T, TK> and
> GlobalLockedBy<S, TK>? Where T is the type protected by the static mutex
> and S is the type protected by the locked_by type?

Something along those lines, yes.

> > no contents, but implements an unsafe trait saying that there's only
> > one static using it.
> >
> > This way we also do not need the helper module, as we no longer need
> > to generate a struct with private fields.
> >
>
> Sounds good to me. Do you plan to let the user name the token type? It's
> fine to me, or do you want to name the token based on the static lock
> name?

The name of the lock has the wrong case, so we can't really reuse it.

Alice