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
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
// This file contains code from external sources.
// Attributions: https://github.com/wasmerio/wasmer/blob/main/docs/ATTRIBUTIONS.md

//! Low-level abstraction for allocating and managing zero-filled pages
//! of memory.

use more_asserts::assert_le;
use std::io;
use std::ptr;
use std::slice;

/// Round `size` up to the nearest multiple of `page_size`.
fn round_up_to_page_size(size: usize, page_size: usize) -> usize {
    (size + (page_size - 1)) & !(page_size - 1)
}

/// A simple struct consisting of a page-aligned pointer to page-aligned
/// and initially-zeroed memory and a length.
#[derive(Debug)]
pub struct Mmap {
    // Note that this is stored as a `usize` instead of a `*const` or `*mut`
    // pointer to allow this structure to be natively `Send` and `Sync` without
    // `unsafe impl`. This type is sendable across threads and shareable since
    // the coordination all happens at the OS layer.
    ptr: usize,
    total_size: usize,
    accessible_size: usize,
    sync_on_drop: bool,
}

/// The type of mmap to create
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
pub enum MmapType {
    /// The memory is private to the process and not shared with other processes.
    Private,
    /// The memory is shared with other processes. This is only supported on Unix.
    /// When the memory is flushed it will update the file data.
    Shared,
}

impl Mmap {
    /// Construct a new empty instance of `Mmap`.
    pub fn new() -> Self {
        // Rust's slices require non-null pointers, even when empty. `Vec`
        // contains code to create a non-null dangling pointer value when
        // constructed empty, so we reuse that here.
        let empty = Vec::<u8>::new();
        Self {
            ptr: empty.as_ptr() as usize,
            total_size: 0,
            accessible_size: 0,
            sync_on_drop: false,
        }
    }

    /// Create a new `Mmap` pointing to at least `size` bytes of page-aligned accessible memory.
    pub fn with_at_least(size: usize) -> Result<Self, String> {
        let page_size = region::page::size();
        let rounded_size = round_up_to_page_size(size, page_size);
        Self::accessible_reserved(rounded_size, rounded_size, None, MmapType::Private)
    }

    /// Create a new `Mmap` pointing to `accessible_size` bytes of page-aligned accessible memory,
    /// within a reserved mapping of `mapping_size` bytes. `accessible_size` and `mapping_size`
    /// must be native page-size multiples.
    #[cfg(not(target_os = "windows"))]
    pub fn accessible_reserved(
        mut accessible_size: usize,
        mapping_size: usize,
        mut backing_file: Option<std::path::PathBuf>,
        memory_type: MmapType,
    ) -> Result<Self, String> {
        use std::os::fd::IntoRawFd;

        let page_size = region::page::size();
        assert_le!(accessible_size, mapping_size);
        assert_eq!(mapping_size & (page_size - 1), 0);
        assert_eq!(accessible_size & (page_size - 1), 0);

        // Mmap may return EINVAL if the size is zero, so just
        // special-case that.
        if mapping_size == 0 {
            return Ok(Self::new());
        }

        // If there is a backing file, resize the file so that its at least
        // `mapping_size` bytes.
        let mut memory_fd = -1;
        if let Some(backing_file_path) = &mut backing_file {
            let file = std::fs::OpenOptions::new()
                .read(true)
                .write(true)
                .open(&backing_file_path)
                .map_err(|e| e.to_string())?;

            let mut backing_file_accessible = backing_file_path.clone();
            backing_file_accessible.set_extension("accessible");

            let len = file.metadata().map_err(|e| e.to_string())?.len() as usize;
            if len < mapping_size {
                std::fs::write(&backing_file_accessible, format!("{}", len).as_bytes()).ok();

                file.set_len(mapping_size as u64)
                    .map_err(|e| e.to_string())?;
            }

            if backing_file_accessible.exists() {
                let accessible = std::fs::read_to_string(&backing_file_accessible)
                    .map_err(|e| e.to_string())?
                    .parse::<usize>()
                    .map_err(|e| e.to_string())?;
                accessible_size = accessible_size.max(accessible);
            } else {
                accessible_size = accessible_size.max(len);
            }

            accessible_size = accessible_size.min(mapping_size);
            memory_fd = file.into_raw_fd();
        }

        // Compute the flags
        let mut flags = match memory_fd {
            fd if fd < 0 => libc::MAP_ANON,
            _ => libc::MAP_FILE,
        };
        flags |= match memory_type {
            MmapType::Private => libc::MAP_PRIVATE,
            MmapType::Shared => libc::MAP_SHARED,
        };

        Ok(if accessible_size == mapping_size {
            // Allocate a single read-write region at once.
            let ptr = unsafe {
                libc::mmap(
                    ptr::null_mut(),
                    mapping_size,
                    libc::PROT_READ | libc::PROT_WRITE,
                    flags,
                    memory_fd,
                    0,
                )
            };
            if ptr as isize == -1_isize {
                return Err(io::Error::last_os_error().to_string());
            }

            Self {
                ptr: ptr as usize,
                total_size: mapping_size,
                accessible_size,
                sync_on_drop: memory_fd != -1 && memory_type == MmapType::Shared,
            }
        } else {
            // Reserve the mapping size.
            let ptr = unsafe {
                libc::mmap(
                    ptr::null_mut(),
                    mapping_size,
                    libc::PROT_NONE,
                    flags,
                    memory_fd,
                    0,
                )
            };
            if ptr as isize == -1_isize {
                return Err(io::Error::last_os_error().to_string());
            }

            let mut result = Self {
                ptr: ptr as usize,
                total_size: mapping_size,
                accessible_size,
                sync_on_drop: memory_fd != -1 && memory_type == MmapType::Shared,
            };

            if accessible_size != 0 {
                // Commit the accessible size.
                result.make_accessible(0, accessible_size)?;
            }

            result
        })
    }

    /// Create a new `Mmap` pointing to `accessible_size` bytes of page-aligned accessible memory,
    /// within a reserved mapping of `mapping_size` bytes. `accessible_size` and `mapping_size`
    /// must be native page-size multiples.
    #[cfg(target_os = "windows")]
    pub fn accessible_reserved(
        accessible_size: usize,
        mapping_size: usize,
        _backing_file: Option<std::path::PathBuf>,
        _memory_type: MmapType,
    ) -> Result<Self, String> {
        use windows_sys::Win32::System::Memory::{
            VirtualAlloc, MEM_COMMIT, MEM_RESERVE, PAGE_NOACCESS, PAGE_READWRITE,
        };

        let page_size = region::page::size();
        assert_le!(accessible_size, mapping_size);
        assert_eq!(mapping_size & (page_size - 1), 0);
        assert_eq!(accessible_size & (page_size - 1), 0);

        // VirtualAlloc may return ERROR_INVALID_PARAMETER if the size is zero,
        // so just special-case that.
        if mapping_size == 0 {
            return Ok(Self::new());
        }

        Ok(if accessible_size == mapping_size {
            // Allocate a single read-write region at once.
            let ptr = unsafe {
                VirtualAlloc(
                    ptr::null_mut(),
                    mapping_size,
                    MEM_RESERVE | MEM_COMMIT,
                    PAGE_READWRITE,
                )
            };
            if ptr.is_null() {
                return Err(io::Error::last_os_error().to_string());
            }

            Self {
                ptr: ptr as usize,
                total_size: mapping_size,
                accessible_size,
                sync_on_drop: false,
            }
        } else {
            // Reserve the mapping size.
            let ptr =
                unsafe { VirtualAlloc(ptr::null_mut(), mapping_size, MEM_RESERVE, PAGE_NOACCESS) };
            if ptr.is_null() {
                return Err(io::Error::last_os_error().to_string());
            }

            let mut result = Self {
                ptr: ptr as usize,
                total_size: mapping_size,
                accessible_size,
                sync_on_drop: false,
            };

            if accessible_size != 0 {
                // Commit the accessible size.
                result.make_accessible(0, accessible_size)?;
            }

            result
        })
    }

    /// Make the memory starting at `start` and extending for `len` bytes accessible.
    /// `start` and `len` must be native page-size multiples and describe a range within
    /// `self`'s reserved memory.
    #[cfg(not(target_os = "windows"))]
    pub fn make_accessible(&mut self, start: usize, len: usize) -> Result<(), String> {
        let page_size = region::page::size();
        assert_eq!(start & (page_size - 1), 0);
        assert_eq!(len & (page_size - 1), 0);
        assert_le!(len, self.total_size);
        assert_le!(start, self.total_size - len);

        // Commit the accessible size.
        let ptr = self.ptr as *const u8;
        unsafe { region::protect(ptr.add(start), len, region::Protection::READ_WRITE) }
            .map_err(|e| e.to_string())
    }

    /// Make the memory starting at `start` and extending for `len` bytes accessible.
    /// `start` and `len` must be native page-size multiples and describe a range within
    /// `self`'s reserved memory.
    #[cfg(target_os = "windows")]
    pub fn make_accessible(&mut self, start: usize, len: usize) -> Result<(), String> {
        use std::ffi::c_void;
        use windows_sys::Win32::System::Memory::{VirtualAlloc, MEM_COMMIT, PAGE_READWRITE};
        let page_size = region::page::size();
        assert_eq!(start & (page_size - 1), 0);
        assert_eq!(len & (page_size - 1), 0);
        assert_le!(len, self.len());
        assert_le!(start, self.len() - len);

        // Commit the accessible size.
        let ptr = self.ptr as *const u8;
        if unsafe {
            VirtualAlloc(
                ptr.add(start) as *mut c_void,
                len,
                MEM_COMMIT,
                PAGE_READWRITE,
            )
        }
        .is_null()
        {
            return Err(io::Error::last_os_error().to_string());
        }

        Ok(())
    }

    /// Return the allocated memory as a slice of u8.
    pub fn as_slice(&self) -> &[u8] {
        unsafe { slice::from_raw_parts(self.ptr as *const u8, self.total_size) }
    }

    /// Return the allocated memory as a slice of u8.
    pub fn as_slice_accessible(&self) -> &[u8] {
        unsafe { slice::from_raw_parts(self.ptr as *const u8, self.accessible_size) }
    }

    /// Return the allocated memory as a slice of u8.
    pub fn as_slice_arbitary(&self, size: usize) -> &[u8] {
        let size = usize::min(size, self.total_size);
        unsafe { slice::from_raw_parts(self.ptr as *const u8, size) }
    }

    /// Return the allocated memory as a mutable slice of u8.
    pub fn as_mut_slice(&mut self) -> &mut [u8] {
        unsafe { slice::from_raw_parts_mut(self.ptr as *mut u8, self.total_size) }
    }

    /// Return the allocated memory as a mutable slice of u8.
    pub fn as_mut_slice_accessible(&mut self) -> &mut [u8] {
        unsafe { slice::from_raw_parts_mut(self.ptr as *mut u8, self.accessible_size) }
    }

    /// Return the allocated memory as a mutable slice of u8.
    pub fn as_mut_slice_arbitary(&mut self, size: usize) -> &mut [u8] {
        let size = usize::min(size, self.total_size);
        unsafe { slice::from_raw_parts_mut(self.ptr as *mut u8, size) }
    }

    /// Return the allocated memory as a pointer to u8.
    pub fn as_ptr(&self) -> *const u8 {
        self.ptr as *const u8
    }

    /// Return the allocated memory as a mutable pointer to u8.
    pub fn as_mut_ptr(&mut self) -> *mut u8 {
        self.ptr as *mut u8
    }

    /// Return the length of the allocated memory.
    pub fn len(&self) -> usize {
        self.total_size
    }

    /// Return whether any memory has been allocated.
    pub fn is_empty(&self) -> bool {
        self.len() == 0
    }

    /// Duplicate in a new memory mapping.
    #[deprecated = "use `copy` instead"]
    pub fn duplicate(&mut self, size_hint: Option<usize>) -> Result<Self, String> {
        self.copy(size_hint)
    }

    /// Duplicate in a new memory mapping.
    pub fn copy(&mut self, size_hint: Option<usize>) -> Result<Self, String> {
        // NOTE: accessible_size != used size as the value is not
        //       automatically updated when the pre-provisioned space is used
        let mut copy_size = self.accessible_size;
        if let Some(size_hint) = size_hint {
            copy_size = usize::max(copy_size, size_hint);
        }

        let mut new =
            Self::accessible_reserved(copy_size, self.total_size, None, MmapType::Private)?;
        new.as_mut_slice_arbitary(copy_size)
            .copy_from_slice(self.as_slice_arbitary(copy_size));
        Ok(new)
    }
}

impl Drop for Mmap {
    #[cfg(not(target_os = "windows"))]
    fn drop(&mut self) {
        if self.total_size != 0 {
            if self.sync_on_drop {
                let r = unsafe {
                    libc::msync(
                        self.ptr as *mut libc::c_void,
                        self.total_size,
                        libc::MS_SYNC | libc::MS_INVALIDATE,
                    )
                };
                assert_eq!(r, 0, "msync failed: {}", io::Error::last_os_error());
            }
            let r = unsafe { libc::munmap(self.ptr as *mut libc::c_void, self.total_size) };
            assert_eq!(r, 0, "munmap failed: {}", io::Error::last_os_error());
        }
    }

    #[cfg(target_os = "windows")]
    fn drop(&mut self) {
        if self.len() != 0 {
            use std::ffi::c_void;
            use windows_sys::Win32::System::Memory::{VirtualFree, MEM_RELEASE};
            let r = unsafe { VirtualFree(self.ptr as *mut c_void, 0, MEM_RELEASE) };
            assert_ne!(r, 0);
        }
    }
}

fn _assert() {
    fn _assert_send_sync<T: Send + Sync>() {}
    _assert_send_sync::<Mmap>();
}

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

    #[test]
    fn test_round_up_to_page_size() {
        assert_eq!(round_up_to_page_size(0, 4096), 0);
        assert_eq!(round_up_to_page_size(1, 4096), 4096);
        assert_eq!(round_up_to_page_size(4096, 4096), 4096);
        assert_eq!(round_up_to_page_size(4097, 4096), 8192);
    }
}