netstack3_base/
settings.rs

1// Copyright 2025 The Fuchsia Authors. All rights reserved.
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5//! Common patterns for runtime configurable settings in netstack.
6
7use core::ops::Deref;
8
9/// Abstracts access to stack settings.
10///
11/// This trait is implemented by *bindings* to allow core access to
12/// runtime-configurable behavior for the network stack.
13///
14/// Separate modules declare their own `T` for settings structures that can be
15/// retrieved via this trait.
16pub trait SettingsContext<T> {
17    /// Borrows the current settings values.
18    fn settings(&self) -> impl Deref<Target = T> + '_;
19}
20
21/// Common settings applied to buffer size configuration.
22///
23/// This type is a witness for a valid configuration where `min <= default <=
24/// max`.
25#[derive(Copy, Clone, Debug, Eq, PartialEq)]
26pub struct BufferSizeSettings<T> {
27    default: T,
28    max: T,
29    min: T,
30}
31
32impl<T: Copy + Ord> BufferSizeSettings<T> {
33    /// Creates a new value with provided `min`, `default`, `max` sizes.
34    ///
35    /// Returns `None` if `min <= default <= max` is violated.
36    pub fn new(min: T, default: T, max: T) -> Option<Self> {
37        if min > default || max < default {
38            return None;
39        }
40        Some(Self { default, max, min })
41    }
42
43    /// Returns the clamped value `val` to the configured maximum and minimum
44    /// buffer sizes.
45    pub fn clamp(&self, val: T) -> T {
46        val.clamp(self.min, self.max)
47    }
48}
49
50impl<T: Copy> BufferSizeSettings<T> {
51    /// Returns the configured default buffer size.
52    pub fn default(&self) -> T {
53        self.default
54    }
55
56    /// Returns the configured maximum buffer size.
57    pub fn max(&self) -> T {
58        self.max
59    }
60
61    /// Returns the configured minimum buffer size.
62    pub fn min(&self) -> T {
63        self.min
64    }
65
66    /// Returns a tuple of the minimum and maximum buffer size, in this order.
67    pub fn min_max(&self) -> (T, T) {
68        (self.min, self.max)
69    }
70}
71
72#[cfg(any(test, feature = "testutils"))]
73pub(crate) mod testutil {
74    use super::*;
75
76    /// A marker trait that allows a type to implement [`SettingsContext`] that
77    /// always yields a default value for the settings type.
78    pub trait AlwaysDefaultsSettingsContext {}
79
80    impl<T, O> SettingsContext<T> for O
81    where
82        T: Default + 'static,
83        O: AlwaysDefaultsSettingsContext,
84    {
85        fn settings(&self) -> impl Deref<Target = T> + '_ {
86            DefaultSettings(T::default())
87        }
88    }
89
90    struct DefaultSettings<T>(T);
91
92    impl<T> Deref for DefaultSettings<T> {
93        type Target = T;
94
95        fn deref(&self) -> &Self::Target {
96            let Self(s) = self;
97            s
98        }
99    }
100}
netstack3_base/settings.rs

netstack3_base/
settings.rs
