Date: Wed, 6 Mar 2024 18:19:12 +0100
To: cygwin@cygwin.com
Subject: Re: ls/stat on OneDrive causes download of files
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From: Corinna Vinschen via Cygwin <cygwin@cygwin.com>
Reply-To: cygwin@cygwin.com
Cc: Corinna Vinschen <corinna-cygwin@cygwin.com>
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On Mar  6 06:54, Brian Inglis via Cygwin wrote:
> On 2024-03-06 06:28, Corinna Vinschen via Cygwin wrote:
> > On Mar  6 14:22, Corinna Vinschen via Cygwin wrote:
> > > Given these placeholder files are actually reparse points of type
> > > IO_REPARSE_TAG_FILE_PLACEHOLDER, we can handle them as symbolic links.
> > > 
> > > However, the structure of the IO_REPARSE_TAG_FILE_PLACEHOLDER reparse
> > > data buffer is undocumented.  It would be helpful if somebody using
> > > OneDrive would examine the content of the attached REPARSE_DATA_BUFFER.
> > > 
> > > > [2] https://github.com/msys2/msys2-runtime/blob/msys2-3.4.10/winsup/cygwin/fhandler/disk_file.cc#L548
> > > 
> > > The NtReadFile call at this point is not the problem.  It would be
> > > helpful to point to Cygwin's source instead of MSYS2, btw.
> > 
> > Oh, btw., this is from
> > https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-fscc/c8e77b37-3909-4fe6-a4ea-2b9d423b1ee4:
> > 
> >    IO_REPARSE_TAG_FILE_PLACEHOLDER
> >    0x80000015
> > 
> >      Obsolete.
> >      ---------
> >      Used by Windows Shell for legacy placeholder files in Windows 8.1.
> >      Server-side interpretation only, not meaningful over the wire.
> > 
> > So even if we support them, what is their replacement in W10 and later?
> 
> May or not help:
> 
> https://stackoverflow.com/questions/59152220/cant-get-reparse-point-information-for-the-onedrive-folder

We can add an explicit call to

  RtlSetProcessPlaceholderCompatibilityMode (PHCM_EXPOSE_PLACEHOLDERS);

and we can recognize the IO_REPARSE_TAG_FILE_PLACEHOLDER and
IO_REPARSE_TAG_CLOUD_* tags during symlink evaluation, but even then
we still have to know what the reparse point buffer actually contains.

Given that the content of reparse points with these reparse tags are
undocumented, some people using cloud services should examine these
reparse points so we can add some suitable code to Cygwin.


Corinna

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