projects/linux·blob master · refs

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1// SPDX-License-Identifier: GPL-2.0
2
3// Copyright (c) 2024 Christian Brauner <[email protected]>
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 {}