Re: [PATCH v5 4/4] rust: samples: Add debugfs sample

[Matthew Maurer <mmaurer@google.com>]

On Wed, May 14, 2025 at 3:14 PM Danilo Krummrich <dakr@kernel.org> wrote:
>
> On Wed, May 14, 2025 at 03:08:21PM -0700, Matthew Maurer wrote:
> > On Wed, May 14, 2025 at 2:54 AM Benno Lossin <lossin@kernel.org> wrote:
> > > Another problem that only affects complicated debugfs structures is that
> > > you would have to store all subdirs & files somewhere. If the structure
> > > is dynamic and changes over the lifetime of the driver, then you'll need
> > > a `Vec` or store the dirs in `Arc` or similar, leading to extra
> > > allocations.
> >
> > Yep, this is part of why I tried to follow the "Build it, then hold
> > the needed handles to keep it alive" approach rather than keeping the
> > entire structure around.
>
> I already replied to that [1]:
>
> "If it changes dynamically then it's pretty likely that we do not only want to
> add entries dynamically, but also remove them, which implies that we need to be
> able to drop them. So, I don't think that's a problem."
>
> It is much more of a problem if we can't remove certain entries anymore without
> removing all of them.
>
> [1] https://lore.kernel.org/rust-for-linux/aCR9cD7OcSefeaUm@pollux/

I think the main question here is this - is it OK to land an API that
does static-layout or add-only-layout first, and we figure out how to
do dynamic modification later, or do you think we need to solve the
self-referential lifetimes issue in the first edition of DebugFS
support?

If you do think we need support for dynamic layout modification in the
first patchset, do you think we want to allow static layouts that
forget things, or mandate that we always manage all of the handles for
the user?