axdevice 0.5.4

A reusable, OS-agnostic device abstraction layer designed for virtual machines.
Documentation 
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145

use alloc::{vec, vec::Vec};
use core::ops::Range;

/// A minimal best-fit range allocator for IVC GPA ranges.
#[derive(Debug)]
pub(crate) struct RangeAllocator {
    initial: Range<usize>,
    free: Vec<Range<usize>>,
}

impl RangeAllocator {
    pub(crate) fn new(range: Range<usize>) -> Self {
        Self {
            initial: range.clone(),
            free: vec![range],
        }
    }

    pub(crate) fn allocate_range(&mut self, size: usize) -> Option<Range<usize>> {
        debug_assert!(size > 0);

        let mut best_fit = None;
        for (index, range) in self.free.iter().enumerate() {
            let len = range.end - range.start;
            if len < size {
                continue;
            }
            if len == size {
                best_fit = Some(index);
                break;
            }
            match best_fit {
                Some(best_index)
                    if len >= self.free[best_index].end - self.free[best_index].start => {}
                _ => best_fit = Some(index),
            }
        }

        let index = best_fit?;
        let start = self.free[index].start;
        let end = start + size;
        if self.free[index].end == end {
            self.free.remove(index);
        } else {
            self.free[index].start = end;
        }
        Some(start..end)
    }

    pub(crate) fn free_range(&mut self, range: Range<usize>) -> bool {
        if range.start >= range.end
            || range.start < self.initial.start
            || range.end > self.initial.end
        {
            return false;
        }

        let index = self
            .free
            .iter()
            .position(|free| free.start > range.start)
            .unwrap_or(self.free.len());

        if index > 0 && self.free[index - 1].end > range.start {
            return false;
        }
        if index < self.free.len() && range.end > self.free[index].start {
            return false;
        }

        if index > 0 && self.free[index - 1].end == range.start {
            self.free[index - 1].end = range.end;
            if index < self.free.len() && self.free[index - 1].end == self.free[index].start {
                let next = self.free.remove(index);
                self.free[index - 1].end = next.end;
            }
        } else if index < self.free.len() && range.end == self.free[index].start {
            self.free[index].start = range.start;
        } else {
            self.free.insert(index, range);
        }

        true
    }
}

#[cfg(test)]
mod tests {
    use super::RangeAllocator;

    #[test]
    fn allocates_and_reuses_ranges() {
        let mut allocator = RangeAllocator::new(0..0x4000);

        assert_eq!(allocator.allocate_range(0x1000), Some(0..0x1000));
        assert_eq!(allocator.allocate_range(0x1000), Some(0x1000..0x2000));

        assert!(allocator.free_range(0..0x1000));
        assert_eq!(allocator.allocate_range(0x1000), Some(0..0x1000));
    }

    #[test]
    fn picks_best_fit_range() {
        let mut allocator = RangeAllocator::new(0..0x9000);

        assert_eq!(allocator.allocate_range(0x3000), Some(0..0x3000));
        assert_eq!(allocator.allocate_range(0x3000), Some(0x3000..0x6000));
        assert_eq!(allocator.allocate_range(0x3000), Some(0x6000..0x9000));

        assert!(allocator.free_range(0..0x3000));
        assert!(allocator.free_range(0x6000..0x9000));

        assert_eq!(allocator.allocate_range(0x3000), Some(0..0x3000));
        assert_eq!(allocator.allocate_range(0x3000), Some(0x6000..0x9000));
    }

    #[test]
    fn merges_neighboring_freed_ranges() {
        let mut allocator = RangeAllocator::new(0..0x3000);

        assert_eq!(allocator.allocate_range(0x1000), Some(0..0x1000));
        assert_eq!(allocator.allocate_range(0x1000), Some(0x1000..0x2000));
        assert_eq!(allocator.allocate_range(0x1000), Some(0x2000..0x3000));

        assert!(allocator.free_range(0..0x1000));
        assert!(allocator.free_range(0x2000..0x3000));
        assert!(allocator.free_range(0x1000..0x2000));

        assert_eq!(allocator.allocate_range(0x3000), Some(0..0x3000));
    }

    #[test]
    fn rejects_invalid_or_duplicate_frees() {
        let mut allocator = RangeAllocator::new(0x1000..0x3000);

        assert!(!allocator.free_range(0x1000..0x1000));
        assert!(!allocator.free_range(0..0x1000));
        assert!(!allocator.free_range(0x2000..0x4000));
        assert!(!allocator.free_range(0x1000..0x2000));

        assert_eq!(allocator.allocate_range(0x1000), Some(0x1000..0x2000));
        assert!(allocator.free_range(0x1000..0x2000));
        assert!(!allocator.free_range(0x1000..0x2000));
    }
}