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perform copy_file_range until EOF is reached instead of basing things…
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… on file size

This solves several problems

- race conditions where a file is truncated while copying from it. if we blindly trusted
  the file size this would lead to an infinite loop
- proc files appearing empty to copy_file_range but not to read/write
  coreutils/coreutils@4b04a0c
- copy_file_range returning 0 for some filesystems (overlay? bind mounts?)
  inside docker, again leading to an infinite loop
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the8472 committed Aug 14, 2020
1 parent f078363 commit 4ddedd5
Showing 1 changed file with 12 additions and 3 deletions.
15 changes: 12 additions & 3 deletions library/std/src/sys/unix/fs.rs
Original file line number Diff line number Diff line change
Expand Up @@ -1140,14 +1140,14 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
}

let (mut reader, reader_metadata) = open_from(from)?;
let len = reader_metadata.len();
let max_len = u64::MAX;
let (mut writer, _) = open_to_and_set_permissions(to, reader_metadata)?;

let has_copy_file_range = HAS_COPY_FILE_RANGE.load(Ordering::Relaxed);
let mut written = 0u64;
while written < len {
while written < max_len {
let copy_result = if has_copy_file_range {
let bytes_to_copy = cmp::min(len - written, usize::MAX as u64) as usize;
let bytes_to_copy = cmp::min(max_len - written, usize::MAX as u64) as usize;
let copy_result = unsafe {
// We actually don't have to adjust the offsets,
// because copy_file_range adjusts the file offset automatically
Expand All @@ -1173,6 +1173,15 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
Err(io::Error::from_raw_os_error(libc::ENOSYS))
};
match copy_result {
Ok(0) if written == 0 => {
// fallback to work around several kernel bugs where copy_file_range will fail to
// copy any bytes and return 0 instead of an error if
// - reading virtual files from the proc filesystem which appear to have 0 size
// but are not empty. noted in coreutils to affect kernels at least up to 5.6.19.
// - copying from an overlay filesystem in docker. reported to occur on fedora 32.
return io::copy(&mut reader, &mut writer);
}
Ok(0) => return Ok(written), // reached EOF
Ok(ret) => written += ret as u64,
Err(err) => {
match err.raw_os_error() {
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