base/sys/linux/
write_zeroes.rs

1// Copyright 2018 The ChromiumOS Authors
2// Use of this source code is governed by a BSD-style license that can be
3// found in the LICENSE file.
4
5use std::cmp::min;
6use std::fs::File;
7use std::io;
8use std::os::unix::fs::FileExt;
9
10use super::discard_block;
11use super::fallocate;
12use super::is_block_file;
13use super::FallocateMode;
14
15pub(crate) fn file_punch_hole(file: &File, offset: u64, length: u64) -> io::Result<()> {
16    if is_block_file(file)? {
17        Ok(discard_block(file, offset, length)?)
18    } else {
19        fallocate(file, FallocateMode::PunchHole, offset, length)
20            .map_err(|e| io::Error::from_raw_os_error(e.errno()))
21    }
22}
23
24pub(crate) fn file_write_zeroes_at(file: &File, offset: u64, length: usize) -> io::Result<usize> {
25    // Try to use fallocate() first.
26    if fallocate(file, FallocateMode::ZeroRange, offset, length as u64).is_ok() {
27        return Ok(length);
28    }
29
30    // fall back to write()
31    // fallocate() failed; fall back to writing a buffer of zeroes
32    // until we have written up to length.
33    let buf_size = min(length, 0x10000);
34    let buf = vec![0u8; buf_size];
35    let mut nwritten: usize = 0;
36    while nwritten < length {
37        let remaining = length - nwritten;
38        let write_size = min(remaining, buf_size);
39        nwritten += file.write_at(&buf[0..write_size], offset + nwritten as u64)?;
40    }
41    Ok(length)
42}
base/sys/linux/write_zeroes.rs

base/sys/linux/
write_zeroes.rs
