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shred: minor improvements and tests #7925

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Merged
merged 2 commits into from
May 21, 2025
Merged

shred: minor improvements and tests #7925

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24d88d7
shred:bitwise method to set OPTIMAL_IO_BLOCK_SIZE
alexs-sh May 12, 2025
14a8f3f
shred:add checks for block sizes
alexs-sh May 12, 2025
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17 changes: 11 additions & 6 deletions src/uu/shred/src/shred.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -49,11 +49,11 @@ const NAME_CHARSET: &[u8] = b"0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMN
const PATTERN_LENGTH: usize = 3;
const PATTERN_BUFFER_SIZE: usize = BLOCK_SIZE + PATTERN_LENGTH - 1;

/// Optimal block size for the filesystem. This constant is used for data size alignment,
/// similar to the behavior of GNU shred. Usually, optimal block size is a 4K block, which is why
/// Optimal block size for the filesystem. This constant is used for data size alignment, similar
/// to the behavior of GNU shred. Usually, optimal block size is a 4K block (2^12), which is why
/// it's defined as a constant. However, it's possible to get the actual size at runtime using, for
/// example, `std::os::unix::fs::MetadataExt::blksize()`.
const OPTIMAL_IO_BLOCK_SIZE: usize = 4096;
const OPTIMAL_IO_BLOCK_SIZE: usize = 1 << 12;

/// Patterns that appear in order for the passes
///
Expand Down Expand Up @@ -514,12 +514,17 @@ fn wipe_file(
}

fn split_on_blocks(file_size: u64, exact: bool) -> (u64, u64) {
// OPTIMAL_IO_BLOCK_SIZE must not exceed BLOCK_SIZE. Violating this may cause overflows due
// to alignment or performance issues.This kind of misconfiguration is
// highly unlikely but would indicate a serious error.
const _: () = assert!(OPTIMAL_IO_BLOCK_SIZE <= BLOCK_SIZE);

let file_size = if exact {
file_size
} else {
// The main idea here is to align the file size to the OPTIMAL_IO_BLOCK_SIZE, and then split it into
// BLOCK_SIZE + remaining bytes. Since the input data is already aligned to N * OPTIMAL_IO_BLOCK_SIZE,
// the output file size will also be aligned and correct.
// The main idea here is to align the file size to the OPTIMAL_IO_BLOCK_SIZE, and then
// split it into BLOCK_SIZE + remaining bytes. Since the input data is already aligned to N
// * OPTIMAL_IO_BLOCK_SIZE, the output file size will also be aligned and correct.
file_size.div_ceil(OPTIMAL_IO_BLOCK_SIZE as u64) * OPTIMAL_IO_BLOCK_SIZE as u64
};
(file_size / BLOCK_SIZE as u64, file_size % BLOCK_SIZE as u64)
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