/bin/cp of sparse files broken in 3.6.0-0.362.g68c13dc92f65.x86_64?

Wed Feb 12 21:34:38 GMT 2025

Corinna Vinschen via Cygwin wrote:
> On Feb 12 17:32, Cedric Blancher via Cygwin wrote:
>> Good afternoon!
>>>> Is copying sparse files broken in 3.6.0-0.362.g68c13dc92f65.x86_64?
>>>> cp --version
>> cp (GNU coreutils) 9.5
>> Packaged by Cygwin (9.5-1
>>>> Checklist:
>> - Volume has FILE_SUPPORTS_SPARSE_FILES
>> - Cygwin mount has "sparse" option (mount Y: -o sparse,exec /cygdrive/y)

Do all mount points below /cygdrive have 'sparse,exec' set?
If not, this may not work because different mount options for individual 
/cygdrive/s are not supported (AFIAK).
>> - source file has FILE_ATTRIBUTE_SPARSE_FILE set
>>>> But cp --sparse=auto ... or any other combination of --sparse does
>> copy holes, i.e. turns 500GB of hole into 500GB of data (zero bytes).
>>>> echo "hello sparse file\n" >testcase17_sparse_begins_with_data && dd
>> if=/dev/null of=testcase17_sparse_begins_with_data oflag=append bs=1
>> count=1 seek=$((65536*512)) && echo "endoffile"
>>>> testcase17_sparse_begins_with_data
> Works for me:
>> $ uname -r
> 3.6.0-0.362.g68c13dc92f65.x86_64
>> $ pwd
> /home/corinna/tmp
>> $ mount | grep tmp
> C:/cygwin64/home/corinna/tmp on /home/corinna/tmp type ntfs (binary,sparse,user,bind)

This mount is independent from /cygdrive. That may make the difference.
-- 
Regards,
Christian