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Date: Tue, 8 Apr 2025 12:47:39 +0200
To: cygwin AT cygwin DOT com
Subject: Re: Windows Remote Driver Identification Re: Cygwin wishlist for
 NFSv4.2 driver?
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From: Corinna Vinschen via Cygwin <cygwin AT cygwin DOT com>
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On Apr  3 14:28, Jeremy Drake via Cygwin wrote:
> On Wed, 2 Apr 2025, Cedric Blancher via Cygwin wrote:
> 
> > On Tue, 1 Apr 2025 at 13:54, Corinna Vinschen via Cygwin
> > <cygwin AT cygwin DOT com> wrote:
> > > No, but if we want to *better* support this driver, we need either a
> > > patch (preferred) or at least info how to distinguish in
> > > fs_info::update(*) between the MSFT driver and the NFSv4.2 driver.
> >
> > That is actually easy: Roland implemented support for
> > FileRemoteProtocolInformation in
> > https://github.com/kofemann/ms-nfs41-client/commit/e9f72b61494bebd9e26fefec2659a4511a05b0fd
> >  , and the FILE_REMOTE_PROTOCOL_INFORMATION->Protocol field can be
> > used to identify the type of driver.
> >
> > Examples:
> > Windows NFSv3 driver uses WNNC_NET_MS_NFS,
> > OpenAFS uses WNNC_NET_OPENAFS, ms-nfs41-client uses
> > WNNC_NET_RDR2SAMPLE, and OpenText NFS also uses WNNC_NET_RDR2SAMPLE.
> >
> > Plan for ms-nfs42-client is to obtain an own WNNC_NET_MSNFS42CLIENT
> > tag, and also tags for DOKANY.
> 
> I thought using WNNC to identify was brought up before and rejected.  At
> this point, it's querying *volume* information, and has a volume handle.
> It looks like you get FileRemoteProtocolInformation by querying a *file*
> handle.  I could be wrong, and maybe that handle can be queried for
> FileRemoteProtocolInformation, but it's not like that returns a unique
> identifier either.

Actually, while the Win32 API requires a volume handle, the underlying
ntdll functions do not.  They only require a handle to a file or directory
opened on the volume which is requested for volume information.

Therefore, if possible, fs_info::update() just reuses the file handle
from the current path_conv check in progress.

Either way, WNNC is not what we're looking for, Jeremy is entirely
on the right path here:

> What I'm seeing of the things that come through volume information:
> FileSystemName is either NFS or DEBUG-NFS41 (the latter at least looks
> unique, if not intended for public consumption).

fsname NFS isn't sufficient obviously.

> The VolumeLabel is
> PnfsVolume, the VolumeSerialNumber is always 0xBABAFACE (that's got to
> suck for the "unique per-drive/share hash" mentioned in mount.cc), the
> flags are set in
> https://github.com/kofemann/ms-nfs41-client/blob/bf8d343ba2465926f3bfafa8407a69e79649cf46/daemon/nfs41_superblock.c#L173

This is a bug in the nfs41 driver.  It should make an effort to generate
a unique serial number and/or a unique volume label.  Why not generate a
hash value from the remote path?  If it can't create a unique VSN, the
VSN should be set to 0.  Otherwise, having the same non-0 VSN for all
mounted NFS shares will lead to confusion.

> What stands out to me in the flags is that they include
> FILE_SUPPORTS_REMOTE_STORAGE.  I'm not sure what that's supposed to
> mean, above and beyond FILE_REMOTE_DEVICE.

https://learn.microsoft.com/en-us/openspecs/windows_protocols/ms-fscc/d4bc551b-7aaf-4b4f-ba0e-3a75e7c528f0#Appendix_A_167

Setting this flag is wrong afaics.

Can somebody with nfs41 installed just run


  $ /usr/lib/csih/getVolInfo <path-to-nfs-share>

and paste the output here?

> MS NFS only seems to set
> FILE_CASE_PRESERVED_NAMES (2), so the existing flag song-and-dance could
> probably be extended to tell the difference here.
> 
> They're also always setting
> SSINFO_FLAGS_ALIGNED_DEVICE|SSINFO_FLAGS_PARTITION_ALIGNED_ON_DEVIVE|
> SSINFO_FLAGS_NO_SEEK_PENALTY.

Could be helpful to distinguish between both NFS versions, but I don't
trust Windows to set the flags if the server is a Windows machine.
Or something.


Corinna

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