[Lzip-bug] lunzip and sparse files

[Tino Lange]

Hi Antonio,

currently I was impressed by "xz" when I extracted a compressed disk 
image file (37 GBytes, will grow to 512 GBytes) accidentally on the wrong 
harddisk (which -- as I thought -- had not enough space for 
decompression, as only 110 GBytes were free on that disk). But: The 
decompression worked! And the file system usage has not changed much 
after decompression.

After wondering how that could be, and after reading a bit I saw that the 
file has been created as "sparse" file, and in fact it did not grow much 
by the "decompression". This is a feature of "xz". sparse files are a 
feature of many file systems, almost all unix file systems, as well as 
NTFS.

Could you add that feature to "l(un)zip" as well?

Test:

$ dd if=/dev/zero of=xz_testfile bs=1024 count=1024
$ dd if=/dev/zero of=lz_testfile bs=1024 count=1024
$ du -h --apparent-size xz_testfile lz_testfile 
1,0M    xz_testfile
1,0M    lz_testfile
$ du -h  xz_testfile lz_testfile 
1,0M    xz_testfile
1,0M    lz_testfile

$ xz xz_testfile 
$ lzip lz_testfile 
$ lunzip lz_testfile.lz 
$ xz -d xz_testfile.xz 

$ du -h --apparent-size xz_testfile lz_testfile 
1,0M    xz_testfile
1,0M    lz_testfile
$ du -h  xz_testfile lz_testfile 
4,0K    xz_testfile
1,0M    lz_testfile

(see that xz testfile has still 4k, although it is apparently 
uncompressed now)


Thanks and cheers,

Tino