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Subject: Re: Writing to '\\.\X:' that has no backing PhysicalDrive?
To: cygwin@cygwin.com
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Date: Thu, 24 Oct 2024 19:50:47 +0200
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From: Christian Franke via Cygwin <cygwin@cygwin.com>
Reply-To: cygwin@cygwin.com
Cc: Christian Franke <Christian.Franke@t-online.de>
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Ilya Basin via Cygwin wrote:
> Hi.
> I was trying to write an .img file to a VeraCrypt drive.
> VeraCrypt doesn't create a virtual PhysicalDrive so tools like Rufus don't see it.
> I hoped that with cygwin I would be able to do that, but Cygwin only creates /dev/sd?? nodes for PhysicalDrive partitions.
> I tried `dd` with '\\.\X:', but it can't open for writing because it treats it as a directory (reading succeeds).
>
> $ dd count=1 if='\\.\E:' | xxd
> 1+0 records in
> 1+0 records out
> 512 bytes copied, 0.0213007 s, 24.0 kB/s
> 00000000: eb52 904e 5446 5320 2020 2000 0208 0000  .R.NTFS    .....
> ...
>
> $ dd if=/dev/null count=0 of='\\.\E:'
> dd: failed to open '\\.\E:': Is a directory

Could reproduce this. The inconsistency between open for reading vs. 
writing of '\\.\E:' is actually interesting. Subtle bug in Cygwin?


>
> Same error in MSYS2.
>
> Does cygwin provide some (hidden) /dev/ nodes for drive letters or volumes like "\\?\Volume{GUID}"? Can I create one with mknod?

Alternatively, VeraCrypt Volumes could be accessed via:

$ ls -l /proc/sys/DosDevices/E:
lr--r--r-- 1 ... /proc/sys/DosDevices/E: -> 
/proc/sys/Device/VeraCryptVolumeE

But /proc/sys is completely R/O like /proc/registry, so you cannot write 
the image via this path.

OT:
/proc/sys/Device/HarddiskVolumeShadowCopyN[/PATH/TO/FILE] allows to read 
the image and individual files from a volume shadow copy.

-- 
Regards,
Christian


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