From 4ddedd521418d67e845ecb43dc02c09b0af53022 Mon Sep 17 00:00:00 2001 From: The8472 Date: Fri, 14 Aug 2020 22:39:04 +0200 Subject: [PATCH] perform copy_file_range until EOF is reached instead of basing things 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 https://github.com/coreutils/coreutils/commit/4b04a0c - copy_file_range returning 0 for some filesystems (overlay? bind mounts?) inside docker, again leading to an infinite loop --- library/std/src/sys/unix/fs.rs | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/library/std/src/sys/unix/fs.rs b/library/std/src/sys/unix/fs.rs index 63af25e3092..566ac0920dc 100644 --- a/library/std/src/sys/unix/fs.rs +++ b/library/std/src/sys/unix/fs.rs @@ -1140,14 +1140,14 @@ unsafe fn copy_file_range( } 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 @@ -1173,6 +1173,15 @@ unsafe fn copy_file_range( 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() { -- GitLab