1// SPDX-License-Identifier: GPL-2.0
 2
 3// Copyright (c) 2024 Christian Brauner <brauner@kernel.org>
 4
 5//! Pid namespaces.
 6//!
 7//! C header: [`include/linux/pid_namespace.h`](srctree/include/linux/pid_namespace.h) and
 8//! [`include/linux/pid.h`](srctree/include/linux/pid.h)
 9
10use crate::{
11    bindings,
12    types::{AlwaysRefCounted, Opaque},
13};
14use core::ptr;
15
16/// Wraps the kernel's `struct pid_namespace`. Thread safe.
17///
18/// This structure represents the Rust abstraction for a C `struct pid_namespace`. This
19/// implementation abstracts the usage of an already existing C `struct pid_namespace` within Rust
20/// code that we get passed from the C side.
21#[repr(transparent)]
22pub struct PidNamespace {
23    inner: Opaque<bindings::pid_namespace>,
24}
25
26impl PidNamespace {
27    /// Returns a raw pointer to the inner C struct.
28    #[inline]
29    pub fn as_ptr(&self) -> *mut bindings::pid_namespace {
30        self.inner.get()
31    }
32
33    /// Creates a reference to a [`PidNamespace`] from a valid pointer.
34    ///
35    /// # Safety
36    ///
37    /// The caller must ensure that `ptr` is valid and remains valid for the lifetime of the
38    /// returned [`PidNamespace`] reference.
39    pub unsafe fn from_ptr<'a>(ptr: *const bindings::pid_namespace) -> &'a Self {
40        // SAFETY: The safety requirements guarantee the validity of the dereference, while the
41        // `PidNamespace` type being transparent makes the cast ok.
42        unsafe { &*ptr.cast() }
43    }
44}
45
46// SAFETY: Instances of `PidNamespace` are always reference-counted.
47unsafe impl AlwaysRefCounted for PidNamespace {
48    #[inline]
49    fn inc_ref(&self) {
50        // SAFETY: The existence of a shared reference means that the refcount is nonzero.
51        unsafe { bindings::get_pid_ns(self.as_ptr()) };
52    }
53
54    #[inline]
55    unsafe fn dec_ref(obj: ptr::NonNull<PidNamespace>) {
56        // SAFETY: The safety requirements guarantee that the refcount is non-zero.
57        unsafe { bindings::put_pid_ns(obj.cast().as_ptr()) }
58    }
59}
60
61// SAFETY:
62// - `PidNamespace::dec_ref` can be called from any thread.
63// - It is okay to send ownership of `PidNamespace` across thread boundaries.
64unsafe impl Send for PidNamespace {}
65
66// SAFETY: It's OK to access `PidNamespace` through shared references from other threads because
67// we're either accessing properties that don't change or that are properly synchronised by C code.
68unsafe impl Sync for PidNamespace {}