Re: [PATCH v4 2/3] rust: pid: add Pid abstraction and init_ns helper

[jongan . kim]

On Wed, Feb 11, 2026 at 10:42:30 +0000, Alice Ryhl wrote:
> On Fri, Feb 06, 2026 at 05:53:35PM +0900, jongan.kim@xxxxxxx wrote:
> > From: HeeSu Kim <heesu0025.kim@xxxxxxx>
> > 
> > Add a new Pid abstraction in rust/kernel/pid.rs that wraps the
> > kernel's struct pid and provides safe Rust interfaces for:
> > - find_vpid: Find a pid by number under RCU protection
> > - pid_task: Get the task associated with a pid under RCU protection
> > 
> > Also add init_ns() associated function to PidNamespace to get
> > a reference to the init PID namespace.
> > 
> > These abstractions use lifetime-bounded references tied to RCU guards
> > to ensure memory safety when accessing RCU-protected data structures.
> > 
> > Suggested-by: Alice Ryhl <aliceryhl@xxxxxxxxxx>
> > Link: https://lore.kernel.org/lkml/aXs3OjlGzQVABAwR@xxxxxxxxxx/
> > Suggested-by: Gary Guo <gary@xxxxxxxxxxx>
> > Link: https://lore.kernel.org/lkml/DG15B78C8IK4.ITL5HKRZ1QKP@xxxxxxxxxxx/
> > Signed-off-by: HeeSu Kim <heesu0025.kim@xxxxxxx>
> > Reviewed-by: Gary Guo <gary@xxxxxxxxxxx>
> 
> > +#ifndef __rust_helper
> > +#define __rust_helper
> > +#endif
> 
> This should not be included. __rust_helper is always defined.
> 
> > +    pub fn find_vpid<'a>(nr: i32, _rcu_guard: &'a rcu::Guard) -> Option<&'a Self> {
> 
> This should use the typedef of pid_t (in task.rs) instead of i32.
> 
> > diff --git a/rust/kernel/pid_namespace.rs b/rust/kernel/pid_namespace.rs
> > index 979a9718f153..fc815945d614 100644
> > --- a/rust/kernel/pid_namespace.rs
> > +++ b/rust/kernel/pid_namespace.rs
> > @@ -38,6 +38,15 @@ pub unsafe fn from_ptr<'a>(ptr: *const bindings::pid_namespace) -> &'a Self {
> >          // `PidNamespace` type being transparent makes the cast ok.
> >          unsafe { &*ptr.cast() }
> >      }
> > +
> > +    /// Returns a reference to the init PID namespace.
> > +    ///
> > +    /// This is the root PID namespace that exists throughout the lifetime of the kernel.
> > +    #[inline]
> > +    pub fn init_ns() -> &'static Self {
> > +        // SAFETY: `init_pid_ns` is a global static that is valid for the lifetime of the kernel.
> > +        unsafe { Self::from_ptr(&raw const bindings::init_pid_ns) }
> > +    }
> 
> This is no longer used anywhere.
> 
> >  }
> >  
> >  // SAFETY: Instances of `PidNamespace` are always reference-counted.
> > @@ -63,3 +72,11 @@ unsafe impl Send for PidNamespace {}
> >  // SAFETY: It's OK to access `PidNamespace` through shared references from other threads because
> >  // we're either accessing properties that don't change or that are properly synchronised by C code.
> >  unsafe impl Sync for PidNamespace {}
> > +
> > +impl PartialEq for PidNamespace {
> > +    fn eq(&self, other: &Self) -> bool {
> > +        self.as_ptr() == other.as_ptr()
> > +    }
> > +}
> > +impl Eq for PidNamespace {}
> 
> This is not used anywhere either.
> 
> Alice

Thank you for feedback.
We will submit the next patch version reflecting your review.
- remove __rust_helper define.
- use pid_t instead of i32
- remove unused implementations in pid_namespace.rs

Best Regards,
Jong An, Kim.