"fd not available for reading or writing" 内存映射文件时

Question

我正在尝试将数据写入 Rust 中的内存映射文件，但它不会对指定文件进行内存映射，因为它声明给定的 fd 不可用。

我可以在文件系统上看到它，所以它确实存在并具有正确的权限。我怀疑这是一个错误，或者我没有以正确的方式使用新的 IO API。

mmap err = fd not available for reading or writing

这是代码

use std::fs::File;
use std::os::MemoryMap;
use std::os::unix::prelude::AsRawFd;
use std::os::MapOption::{MapFd, MapWritable, MapReadable};

fn main() {
    let f = File::create("test.dat").unwrap();
    f.set_len(n as u64);

    let fd = f.as_raw_fd();

    let mmap = MemoryMap::new(n, &[MapReadable, MapWritable, MapFd(fd)]);

    match mmap {
        Ok(_) => println!("mmap success"),
        Err(ref err) => println!("mmap err = {}", err),
    }
}

Answer 1

使用 File::create are in write-only mode, but you are attempting to map the file for both reading and writing. Use OpenOptions 创建的文件以获取具有两种模式的文件：

#![feature(os, std_misc)]

use std::fs::OpenOptions;
use std::os::MemoryMap;
use std::os::unix::prelude::AsRawFd;
use std::os::MapOption::{MapFd, MapReadable, MapWritable};

fn main() {
    let n = 100;

    let f = OpenOptions::new()
        .read(true)
        .write(true)
        .truncate(true)
        .create(true)
        .open("test.dat")
        .unwrap();

    f.set_len(n as u64).unwrap();

    let fd = f.as_raw_fd();

    let mmap = MemoryMap::new(n, &[MapReadable, MapWritable, MapFd(fd)]);

    match mmap {
        Ok(_) => println!("mmap success"),
        Err(err) => println!("mmap err = {}", err),
    }
}

我想通了

Grepping "fd not available for reading or writing" 的代码，这导致 this line，与 ErrFdNotAvail 对齐（也可以将 mmap err = {} 更改为 mmap err = {:?}).
搜索该枚举变体会导致 this line，它映射了潜在的 libc::EACCES 错误。
查看 man page for mmap 看看 EACCES 说了什么：

The flag PROT_READ was specified as part of the prot argument and fd was not open for reading. The flags MAP_SHARED and PROT_WRITE were specified as part of the flags and prot argument and fd was not open for writing.

"fd not available for reading or writing" 内存映射文件时

"fd not available for reading or writing" when memory-mapping a file

rust