pid_namespace.rs

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