Re: [PATCH] Cygwin: Add /dev/disk/by-id symlinks

[Corinna Vinschen <corinna-cygwin@cygwin.com>]

On Nov  3 17:09, Christian Franke wrote:
> Corinna Vinschen wrote:
> > I haven't found out where the UUID is coming from, yet, but based on the
> > description from
> > https://learn.microsoft.com/en-us/windows-hardware/drivers/storage/device-unique-identifiers--duids--for-storage-devices
> > I came up with this Q&D solution:
> > 
> > =============== SNIP ================
> > diff --git a/winsup/cygwin/fhandler/dev_disk.cc b/winsup/cygwin/fhandler/dev_disk.cc
> > index caca57d63216..74abfb8a3288 100644
> > --- a/winsup/cygwin/fhandler/dev_disk.cc
> > +++ b/winsup/cygwin/fhandler/dev_disk.cc
> > @@ -36,29 +36,51 @@ sanitize_id_string (char *s)
> >     return i;
> >   }
> > +typedef struct _STORAGE_DEVICE_UNIQUE_IDENTIFIER {
> > +  ULONG Version;
> > +  ULONG Size;
> > +  ULONG StorageDeviceIdOffset;
> > +  ULONG StorageDeviceOffset;
> > +  ULONG DriveLayoutSignatureOffset;
> > +} STORAGE_DEVICE_UNIQUE_IDENTIFIER, *PSTORAGE_DEVICE_UNIQUE_IDENTIFIER;
> > +
> > +typedef struct _STORAGE_DEVICE_LAYOUT_SIGNATURE {
> > +  ULONG   Version;
> > +  ULONG   Size;
> > +  BOOLEAN Mbr;
> > +  union {
> > +    ULONG MbrSignature;
> > +    GUID  GptDiskId;
> > +  } DeviceSpecific;
> > +} STORAGE_DEVICE_LAYOUT_SIGNATURE, *PSTORAGE_DEVICE_LAYOUT_SIGNATURE;
> > +
> 
> These are available in storduid.h

Yeah, and defining STORAGE_DEVICE_LAYOUT_SIGNATURE is useless,
but it was just for PoC.

> Thanks. Using this makes plenty of sense as a fallback if the serial number
> is unavailable. But if available, the serial number should be in the
> generated name as on Linux. This would provide a persistent name which
> reflects the actual device without a number invented by MS.

ACK

> The serial number is usually available with (S)ATA and NVMe (namespace uuid
> in the latter case). I'm not familiar with QEMU/KVM details. The fact that
> both 'vendor' and 'product' are returned on your system suggests that a
> SCSI/SAS controller is emulated.

Yes.

> Unlike (S)ATA and NVMe, the serial number
> is not available for free in the device identify data block but requires an
> extra command (SCSI INQUIRY of VPD page 0x80). This might not be supported
> by the emulated controller or Windows does not use this command.

AFAICS, only the data from STORAGE_DEVICE_ID_DESCRIPTOR is available
which is equivalent to the data from VPD page 0x83.  As you can see,
it's part of the STORAGE_DEVICE_UNIQUE_IDENTIFIER data.  The data
returned for the VirtIo device is the identifier string "\x01\x00",
which is a bit underwhelming.

Would be great if we would learn how to access page 0x80...

> IIRC the serial number is sometimes available via WMI even if missing in
> IOCTL_STORAGE_QUERY_PROPERTY:
> 
>   wmic diskdrive get manufacturer,model,serialnumber

Nope, it returns an empty string, just as the date from
STORAGE_DEVICE_DESCRIPTOR.


Corinna