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Subject:	Re: /bin/cp of sparse files broken in
	3.6.0-0.362.g68c13dc92f65.x86_64?
To:	cygwin AT cygwin DOT com
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	<Z6zasFeEi1cavLyr AT calimero DOT vinschen DOT de>
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Message-ID:	<98bf943a-8a80-dd8d-d515-923ce1f5acf8@t-online.de>
Date:	Sat, 15 Feb 2025 13:53:04 +0100
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From:	Christian Franke via Cygwin <cygwin AT cygwin DOT com>
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Cc:	Christian Franke <Christian DOT Franke AT t-online DOT de>
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Corinna Vinschen via Cygwin wrote:
> On Feb 15 11:17, Corinna Vinschen via Cygwin wrote:
>> https://cygwin.com/cygwin-ug-net/using.html#cygdrive
> I uploaded the new 3.6 version of that chapter to cygwin.com, btw.
>
>

BTW, the info "sparse ... This flag is always silently enabled on SSD 
drives" is only here:
   https://cygwin.com/cygwin-ug-net/mount.html
but not here:
   https://cygwin.com/cygwin-ug-net/using.html#mount-table


Note that, thanks to Cygwin's support of FALLOC_FL_PUNCH_HOLE, sparse 
files may also be created on non-sparse mounts if 'cp --sparse=always' 
is used.

In some use cases requiring only single sparse files (e.g. create disk 
images with dd or ddrescue), it is also possible to preset the sparse 
attribute.

Examples (on HDD):

$ uname -r
3.6.0-0.374.g4dd859d01c22.x86_64

$ cp --version
cp (GNU coreutils) 9.6
Packaged by Cygwin (9.6-1)
...
$ dd if=/dev/zero bs=1M count=1 >file; echo EOF >>file

$ cp file file-cp

$ cp --sparse=always file file-cp-sparse-always

$ dd if=file conv=sparse of=file-dd
...
$ >file-dd-chattr-sparse

$ chattr +S file-dd-chattr-sparse

$ dd if=file conv=sparse,notrunc of=file-dd-chattr-sparse
...
$ lsattr file*
---a---------- file
---a---------- file-cp
---a-S-------- file-cp-sparse-always
---a---------- file-dd
---a-S-------- file-dd-chattr-sparse

$ stat -c "%5b %s %n" file*
  1028 1048580 file
  1028 1048580 file-cp
    64 1048580 file-cp-sparse-always
  1028 1048580 file-dd
    64 1048580 file-dd-chattr-sparse

On a SSD, 'file-dd' would also be sparse.

-- 
Regards,
Christian



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