Re: [PATCH v7 1/4] lib/vsprintf: Export functions for Rust pointer formatting support

[Alice Ryhl <aliceryhl@google.com>]

On Mon, Dec 29, 2025 at 04:18:57PM +0200, Andy Shevchenko wrote:
> On Mon, Dec 29, 2025 at 03:21:19PM +0800, Ke Sun wrote:
> > Export ptr_to_hashval() and extract kptr_restrict_value() to enable
> > Rust code to use kernel pointer formatting functionality.
> > 
> > - Export ptr_to_hashval() with EXPORT_SYMBOL_GPL for pointer hashing.
> >   This function is used to hash kernel pointers before printing them,
> >   preventing information leaks about kernel memory layout.
> > 
> > - Extract kptr_restrict handling logic from restricted_pointer() into
> >   a separate exported function kptr_restrict_value() that can be
> >   reused by both restricted_pointer() (for %pK format specifier) and
> >   Rust code.
> > 
> > The kptr_restrict_value() function:
> > - Returns 0, 1, or 2 to indicate the kptr_restrict sysctl value
> > - Returns -1 for error case (IRQ context with kptr_restrict==1)
> > - Modifies the pointer value through @pptr parameter when needed
> >   (sets to NULL when access should be restricted)
> > 
> > These functions are needed for the HashedPtr and RestrictedPtr wrapper
> > types in rust/kernel/ptr.rs to provide safe pointer formatting that
> > matches C kernel patterns.
> > 
> > This refactoring:
> > - Allows restricted_pointer() to reuse the common logic while
> >   maintaining the same behavior
> > - Enables Rust code to use the same kptr_restrict handling logic
> > - Reduces code duplication
> 
> ...
> 
> > +EXPORT_SYMBOL_GPL(ptr_to_hashval);
> 
> I do not like this. At bare minimum we should make sure it's namespaced, so the
> author of the code deliberately needs to import it (I'm talking about C side).
> 
> Ideally we should have something which is Rust specific, like
> 
> EXPORT_SYMBOL_FOR_RUST_ONLY(foo);
> 
> Can we do that first?

We don't have an EXPORT_SYMBOL_FOR_RUST_ONLY(). The closest there is
would be to place it in rust/helpers/, since such symbols won't be
available to C modules once we land this:

https://lore.kernel.org/all/20251202-inline-helpers-v1-0-879dae33a66a@google.com/

But since the current file also needs to access this, I don't think it
will fly.

Alice