shred: add 4K data alignment #7915
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This commit allows aligning output data by 4K to better match GNU shred. The 4K block size is configured as a constant because it provides a widely used value in the simplest way. However, there is a chance that some systems may use a different value. So far, I haven't encountered anything other than 4K, I decided not to overcomplicate the approach for now.
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GNU testsuite comparison: |
This commit improves the reliability of the writing logic and removes implicit dependencies between the preferred I/O size and the block size. For example, in earlier versions, using BLOCK_SIZE != N * IO_SIZE could lead to overflows due to alignment with values larger than the buffer size.
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GNU testsuite comparison: |
BenWiederhake
approved these changes
May 11, 2025
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Thank you for your feedback and quick review |
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About
This PR continues the work on issue #7870. It adds 4K alignment of output data to better matching with GNU shred behavior. Updating the alignment, but not the application's block size, allows to avoid the performance degradation observed in shred: use 4K block PR.
Before
After
Expected
I also tested a few more control values (1,4095,4096,4097,65535,65536,65537) to compare GNU shred with uutils shred. With these changes, both apps produce the same output.
GNU shred
Modified uutils shred