Function nc::mmap

source · 
pub unsafe fn mmap(
    start: usize,
    len: size_t,
    prot: i32,
    flags: i32,
    fd: i32,
    offset: off_t
) -> Result<usize, Errno>
Expand description

Map files or devices into memory.

§Example

let path = "/etc/passwd";
let ret = unsafe { nc::openat(nc::AT_FDCWD, path, nc::O_RDONLY, 0o644) };
assert!(ret.is_ok());
let fd = ret.unwrap();

let mut sb = nc::stat_t::default();
let ret = unsafe { nc::fstat(fd, &mut sb) };
assert!(ret.is_ok());

let offset: usize = 0;
let length: usize = sb.st_size as usize - offset;
// Offset for mmap must be page aligned.
let pa_offset: usize = offset & !(nc::PAGE_SIZE - 1);
let map_length = length + offset - pa_offset;

let addr = unsafe {
    nc::mmap(
        0, // 0 as NULL
        map_length,
        nc::PROT_READ,
        nc::MAP_PRIVATE,
        fd,
        pa_offset as nc::off_t,
    )
};
assert!(addr.is_ok());
let addr = addr.unwrap();

let n_write = unsafe { nc::write(1, addr + offset - pa_offset, length) };
assert!(n_write.is_ok());
assert_eq!(n_write, Ok(length as nc::ssize_t));
let ret = unsafe { nc::munmap(addr, map_length) };
assert!(ret.is_ok());
let ret = unsafe { nc::close(fd) };
assert!(ret.is_ok());
Examples found in repository?
examples/mmap.rs (lines 34-41)
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fn main() {
    let path = "/etc/passwd";
    let fd = unsafe { nc::openat(nc::AT_FDCWD, path, nc::O_RDONLY, 0o644) };
    assert!(fd.is_ok());
    let fd = fd.unwrap();

    let mut sb = nc::stat_t::default();
    let ret = unsafe { nc::fstat(fd, &mut sb) };
    assert!(ret.is_ok());

    let offset: usize = 0;
    let length: usize = sb.st_size as usize - offset;
    // Offset for mmap must be page aligned.
    let pa_offset: usize = offset & !(nc::PAGE_SIZE - 1);
    let map_length = length + offset - pa_offset;

    #[cfg(target_arch = "arm")]
    let addr = unsafe {
        nc::mmap2(
            0, // 0 as NULL
            map_length,
            nc::PROT_READ,
            nc::MAP_PRIVATE,
            fd,
            pa_offset as nc::off_t,
        )
    };
    #[cfg(not(target_arch = "arm"))]
    let addr = unsafe {
        nc::mmap(
            0, // 0 as NULL
            map_length,
            nc::PROT_READ,
            nc::MAP_PRIVATE,
            fd,
            pa_offset as nc::off_t,
        )
    };
    assert!(addr.is_ok());

    let addr = addr.unwrap();
    let n_write = unsafe { nc::write(1, addr + offset - pa_offset, length) };
    assert!(n_write.is_ok());
    assert_eq!(n_write, Ok(length as nc::ssize_t));
    let ret = unsafe { nc::munmap(addr, map_length) };
    assert!(ret.is_ok());
    let ret = unsafe { nc::close(fd) };
    assert!(ret.is_ok());
}
More examples
Hide additional examples
examples/mprotect.rs (lines 46-53)
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fn main() {
    // Register SIGSEGV handler.
    let sa = nc::sigaction_t {
        sa_handler: handle_segfault as nc::sighandler_t,
        sa_flags: nc::SA_SIGINFO,
        ..nc::sigaction_t::default()
    };
    let mut old_sa = nc::sigaction_t::default();
    let ret = unsafe {
        nc::rt_sigaction(
            nc::SIGSEGV,
            &sa,
            &mut old_sa,
            mem::size_of::<nc::sigset_t>(),
        )
    };
    assert!(ret.is_ok());

    // Initialize an anonymous mapping with 4 pages.
    let map_length = 4 * nc::PAGE_SIZE;
    #[cfg(target_arch = "arm")]
    let addr = unsafe {
        nc::mmap2(
            0,
            map_length,
            nc::PROT_READ | nc::PROT_WRITE,
            nc::MAP_PRIVATE | nc::MAP_ANONYMOUS,
            -1,
            0,
        )
    };

    #[cfg(not(target_arch = "arm"))]
    let addr = unsafe {
        nc::mmap(
            0,
            map_length,
            nc::PROT_READ | nc::PROT_WRITE,
            nc::MAP_PRIVATE | nc::MAP_ANONYMOUS,
            -1,
            0,
        )
    };
    assert!(addr.is_ok());
    let addr = addr.unwrap();

    // Set the third page readonly. And we will run into SIGSEGV when updating it.
    let ret = unsafe { nc::mprotect(addr + 2 * nc::PAGE_SIZE, nc::PAGE_SIZE, nc::PROT_READ) };
    assert!(ret.is_ok());

    for p in addr..(addr + map_length) {
        unsafe {
            *(p as *mut u8) = 42;
        }
    }

    let ret = unsafe { nc::munmap(addr, map_length) };
    assert!(ret.is_ok());
    unsafe { nc::exit(0) };
}