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WIMLIB WIMBOOT Extraction with NTFS Compression Attribute

Posted: Wed Dec 05, 2018 5:46 pm
by zipmagic
WIMLIB retains NTFS compression attributes and restores these attributes when applying a WIM image in WIMBOOT mode.

As documented on this thread:


The current WIMLIB workflow for WIM image application in WIMBOOT mode leads to undesirable behavior:

1.) File is created, but no data is written yet.
2.) FILE_ATTRIBUTE_COMPRESSED is set if needed to match the state in the WIM file. Again, no data is written yet.
3.) FSCTL_SET_EXTERNAL_BACKING is used to mark the file's contents as externally backed by the WIM file.

Subsequently, Windows File Explorer will show all affected files as NTFS compressed, when in fact none are NTFS compressed.

Suggested Fix: Only when applying an image in WIMBOOT mode, provide an option (or default to) not setting the NTFS compression attribute on the file.

Applying a WIM image in WIMBOOT mode does not actually apply NTFS compression on any of the files marked as NTFS compressed, at least not until those files are modified.