Struct memmap::MmapOptions

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pub struct MmapOptions { /* private fields */ }

Expand description

A memory map builder, providing advanced options and flags for specifying memory map behavior.

MmapOptions can be used to create an anonymous memory map using MmapOptions::map_anon, or a file-backed memory map using one of MmapOptions::map, MmapOptions::map_mut, MmapOptions::map_exec, or MmapOptions::map_copy.

Implementations

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impl MmapOptions

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pub fn new() -> MmapOptions

Creates a new set of options for configuring and creating a memory map.

Example

use memmap::{MmapMut, MmapOptions};

// Create a new memory map builder.
let mut mmap_options = MmapOptions::new();

// Configure the memory map builder using option setters, then create
// a memory map using one of `mmap_options.map_anon`, `mmap_options.map`,
// `mmap_options.map_mut`, `mmap_options.map_exec`, or `mmap_options.map_copy`:
let mut mmap: MmapMut = mmap_options.len(36).map_anon()?;

// Use the memory map:
mmap.copy_from_slice(b"...data to copy to the memory map...");

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pub fn offset(&mut self, offset: usize) -> &mut Self

Configures the memory map to start at byte offset from the beginning of the file.

This option has no effect on anonymous memory maps.

By default, the offset is 0.

Example

use memmap::MmapOptions;
use std::fs::File;

let mmap = unsafe {
    MmapOptions::new()
                .offset(10)
                .map(&File::open("README.md")?)?
};
assert_eq!(&b"A Rust library for cross-platform memory mapped IO."[..],
           &mmap[..51]);

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pub fn len(&mut self, len: usize) -> &mut Self

Configures the created memory mapped buffer to be len bytes long.

This option is mandatory for anonymous memory maps.

For file-backed memory maps, the length will default to the file length.

Example

use memmap::MmapOptions;
use std::fs::File;

let mmap = unsafe {
    MmapOptions::new()
                .len(8)
                .map(&File::open("README.md")?)?
};
assert_eq!(&b"# memmap"[..], &mmap[..]);

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pub fn stack(&mut self) -> &mut Self

Configures the anonymous memory map to be suitable for a process or thread stack.

This option corresponds to the MAP_STACK flag on Linux.

This option has no effect on file-backed memory maps.

Example

use memmap::MmapOptions;

let stack = MmapOptions::new().stack().len(4096).map_anon();

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pub unsafe fn map(&self, file: &File) -> Result<Mmap>

Creates a read-only memory map backed by a file.

Errors

This method returns an error when the underlying system call fails, which can happen for a variety of reasons, such as when the file is not open with read permissions.

Example

use memmap::MmapOptions;
use std::fs::File;
use std::io::Read;

let mut file = File::open("README.md")?;

let mut contents = Vec::new();
file.read_to_end(&mut contents)?;

let mmap = unsafe {
    MmapOptions::new().map(&file)?
};

assert_eq!(&contents[..], &mmap[..]);

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pub unsafe fn map_exec(&self, file: &File) -> Result<Mmap>

Creates a readable and executable memory map backed by a file.

Errors

This method returns an error when the underlying system call fails, which can happen for a variety of reasons, such as when the file is not open with read permissions.

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pub unsafe fn map_mut(&self, file: &File) -> Result<MmapMut>

Creates a writeable memory map backed by a file.

Errors

This method returns an error when the underlying system call fails, which can happen for a variety of reasons, such as when the file is not open with read and write permissions.

Example

use std::fs::OpenOptions;
use std::path::PathBuf;

use memmap::MmapOptions;
let path: PathBuf = /* path to file */
let file = OpenOptions::new().read(true).write(true).create(true).open(&path)?;
file.set_len(13)?;

let mut mmap = unsafe {
    MmapOptions::new().map_mut(&file)?
};

mmap.copy_from_slice(b"Hello, world!");

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pub unsafe fn map_copy(&self, file: &File) -> Result<MmapMut>

Creates a copy-on-write memory map backed by a file.

Data written to the memory map will not be visible by other processes, and will not be carried through to the underlying file.

Errors

This method returns an error when the underlying system call fails, which can happen for a variety of reasons, such as when the file is not open with writable permissions.

Example

use memmap::MmapOptions;
use std::fs::File;
use std::io::Write;

let file = File::open("README.md")?;
let mut mmap = unsafe { MmapOptions::new().map_copy(&file)? };
(&mut mmap[..]).write_all(b"Hello, world!")?;