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Re: [PATCH] Fix stat.st_blocks for files compressed with CompactOS method


Corinna Vinschen wrote:
Hi Christian,

On Apr 22 14:50, Christian Franke wrote:
Cygwin 2.8.0 returns stat.st_blocks = 0 if a file is compressed with
CompactOS method (at least on Win10 1607):
[...]
This is because StandardInformation.AllocationSize is always 0 for theses
files. CompressedFileSize returns the correct value.

This is likely related to the interesting method how these files are encoded
in the MFT:
The default $DATA stream is a sparse stream with original size but no
allocated blocks.
An alternate $DATA stream WofCompressedData contains the compressed data.
An additional $REPARSE_POINT possibly marks this file a special and lets
accesses fail on older Windows releases (and on Linux, most current forensic
tools, ...).

With the attached patch, stat.st_blocks work as expected:
[...]
-  else if (::has_attribute (attributes, FILE_ATTRIBUTE_COMPRESSED
-					| FILE_ATTRIBUTE_SPARSE_FILE)
+  else if ((pfai->StandardInformation.AllocationSize.QuadPart == 0LL
+	    || ::has_attribute (attributes, FILE_ATTRIBUTE_COMPRESSED
+					  | FILE_ATTRIBUTE_SPARSE_FILE))
Are you saying these files actually have no FILE_ATTRIBUTE_COMPRESSED
bit set???


Yes. The only evidence is the CompressedSize.
There is also no visual emphasis in explorer listings.

Christian


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