1 // Copyright 2022 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
5 use std::cmp::min;
6 use std::fs::File;
7 use std::io;
8 use std::os::windows::fs::FileExt;
9
10 use crate::PunchHole;
11
12 // TODO(b/195151495): Fix so that this will extend a file size if needed.
file_write_zeroes_at( file: &mut File, offset: u64, length: usize, ) -> io::Result<usize>13 pub(crate) fn file_write_zeroes_at(
14 file: &mut File,
15 offset: u64,
16 length: usize,
17 ) -> io::Result<usize> {
18 // Try to punch a hole first.
19 if let Ok(()) = file.punch_hole(offset, length as u64) {
20 return Ok(length);
21 }
22
23 // fall back to write()
24 // punch_hole() failed; fall back to writing a buffer of zeroes
25 // until we have written up to length.
26 let buf_size = min(length, 0x10000);
27 let buf = vec![0u8; buf_size];
28 let mut nwritten: usize = 0;
29 while nwritten < length {
30 let remaining = length - nwritten;
31 let write_size = min(remaining, buf_size);
32 nwritten += file.seek_write(&buf[0..write_size], offset + nwritten as u64)?;
33 }
34 Ok(length)
35 }
36