Wrong Allocated Size for Sparse Files if Read from Cache File

[spacekpe]

Hello,

and thank you for an awesome software and all the work you put into it over the years!

Here is a bug report about the latest version:

Version:

• qdirstat 1.8
• qt5-base 5.15.2

Observed behavior:

• Sparse files are detected correctly when scanning filesystem from GUI
• Apparent and allocated sparse file sizes seem to be written correctly to .qdirstat.cache.gz file generated from GUI
• GUI displays incorrect Allocated size when reading cache file generated by itself

Reproducer:

• generate sparse file

dd if=/dev/zero of=sparse count=1 seek=100 bs=1M

• generate cache file of the directory either in GUI or using

qdirstat-cache-writer .

• load the cache file into the GUI

• Screenshot of "live scan" - sizes are okay:
  

• Screenshot of cache read - allocated size is incorrect:
  

• cache file to reproduce the problem:
  .qdirstat.cache.gz

Please let me know what other information you need.

[shundhammer]

You are right; good catch!

For a moment I thought it's a problem of the cache writer to write incorrect numbers of blocks to the cache for sparse files, but AFAICS that's actually correct:

[sh @ balrog] ~/tmp 6 % zcat work-test-sparse.cache.gz
[qdirstat 1.0 cache file]
# Do not edit!
#
# Type	path		size	mtime		<optional fields>

D /work/test/sparse	4K	0x5ee8e19d
F	sparse-8k-zero	8K	0x5ee8e19d	blocks: 0
F	sparse-8k	8K	0x5ee8e1a2	blocks: 8
F	sparse-zero.bin	1000M	0x56b499f6	blocks: 0
F	sparse-1MB.bin	1001M	0x56b49a1c	blocks: 2048

(Using the sparse/ subdirectory from QDirStat's test data at https://github.com/shundhammer/qdirstat/tree/master/test/data)

Reading back those data from a cache file shows "allocated: 0 Bytes" for all sparse files which is wrong for sparse-8k and sparse-1MB.bin:

[shundhammer]

This affects only sparse files when read from a cache file. Non-sparse files are displayed correctly.

[shundhammer]

The fix was adding the missing case in the FileInfo item constructor for cached items: If there is a blocks: field for this item in the cache file, it is now correctly used to initialize the item's internal _allocatedSize field.

Petr, thanks for finding and reporting this!

[spacekpe]

Wow, thank was fast! Thank you!