Re: Size limitation for NcFsd drive?

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

Franz?  Ping?


Thx,
Corinna

On Aug  2 16:59, Corinna Vinschen wrote:
> Hi Franz,
> 
> On Aug  2 16:26, Franz Sirl wrote:
> > Am 2016-07-29 um 16:38 schrieb Corinna Vinschen:
> > > On Jul 29 16:18, Corinna Vinschen wrote:
> > > > In the first place it would be prudent to find out why the
> > > > FileAllInformation info class fails on this drive.  And in the second
> > > > place it would be important to find out how to fix this.  Potential
> > > > checks:
> > > > 
> > > > - Buffer alignment of the FILE_ALL_INFORMATION member in class
> > > >   path_conv_handle.
> > > > 
> > > > - Buffer size of the FILE_ALL_INFORMATION member.  For instance,
> > > >   does it work if the buffer is 1 byte bigger?  Or perhaps if
> > > >   the buffer is NAME_MAX bigger?
> > > 
> > > - There's also a chance (albeit minor) that the FileAllInformation call
> > >   actually worked and the weird status code is just wrong.  After all,
> > >   returning from this call with STATUS_BUFFER_OVERFLOW is valid, too,
> > >   so I'd check for this as well here.
> > 
> > Hi Corinna,
> > 
> > no, the error code isn't influenced by alignment or size. For local drives
> > and SMB shares the STATUS_BUFFER_OVERFLOW turns into STATUS_SUCCESS as soon
> > as there is enough room for the share path in the
> > FILE_NAME_INFORMATION.FileName flexible array member (actually, why isn't
> > path_conv_handle.attribs._fai larger? performance? FileNameInformation
> > usually not needed?).
> 
> FileNameInformation is the full path to the file.  It's not only not
> needed, but for full long pathname support the buffer would have to
> be sizeof (FILE_ALL_INFORMATION) + 32767 * sizeof (WCHAR), thus more
> than 64K in size.
> 
> FileAllInformation is designed so that you can ask for all information
> except the filename by just ignoring the name buffer requirements.  In
> that case NtQueryInformationFile returns STATUS_BUFFER_OVERFLOW, which
> can be ignored.
> 
> > But for the NCP share the strange error code for
> > FileAllInformation remains. Checking all the members of FileAllInformation
> > one by one, it turned out that it's the FileInternalIformation member that
> > fails. I've reported it as a bug to Novell.
> 
> Cool.  NtQueryInformationFile is supposed to just set all unsupported
> members to 0, see the Remarks section of
> https://msdn.microsoft.com/en-us/library/windows/hardware/ff567052(v=vs.85).aspx
> 
> However, do we need a workaround?  Kind of like this:
> 
> diff --git a/winsup/cygwin/path.cc b/winsup/cygwin/path.cc
> index 970a0fe..d9ed357 100644
> --- a/winsup/cygwin/path.cc
> +++ b/winsup/cygwin/path.cc
> @@ -1307,6 +1307,19 @@ file_get_fai (HANDLE h, PFILE_ALL_INFORMATION pfai)
>  				   FileAllInformation);
>    if (status == STATUS_BUFFER_OVERFLOW)
>      status = STATUS_SUCCESS;
> +  /* Filesystems with broken FileAllInformation exist, too.  See the thread
> +     starting with https://cygwin.com/ml/cygwin/2016-07/msg00350.html. */
> +  else if (!NT_SUCCESS (status) && status != STATUS_ACCESS_DENIED)
> +    {
> +      memset (pfai, 0, sizeof *pfai);
> +      status = NtQueryInformationFile (h, &io, &pfai->BasicInformation,
> +				       sizeof pfai->BasicInformation,
> +				       FileBasicInformation);
> +      if (NT_SUCCESS (status))
> +	status = NtQueryInformationFile (h, &io, &pfai->StandardInformation,
> +					 sizeof pfai->StandardInformation,
> +					 FileStandardInformation);
> +    }
>    return status;
>  }
>  
> 
> > Nevertheless I believe the fallback to
> > NtQueryDirectoryFile(FileIdBothDirectoryInformation) does not do what you
> > want if the path is the root directory of a share. But that's not the cause
> > of this problem.
> 
> Yeah, as I wrote in my reply, the NtQueryDirectoryFile branch isn't
> supposed to be hit in this scenario.  It's solely for "access denied"
> situations.
> 
> Are you set up to build your own Cygwin DLL so you can test the above
> patch locally?
> 
> 
> Thanks,
> Corinna
> 
> -- 
> Corinna Vinschen                  Please, send mails regarding Cygwin to
> Cygwin Maintainer                 cygwin AT cygwin DOT com
> Red Hat



-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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