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

[Christian Franke <Christian.Franke@t-online.de>]

Corinna Vinschen wrote:
> On Nov  4 10:34, Corinna Vinschen wrote:
>> On Nov  3 18:54, Christian Franke wrote:
>>> ...
>>>> MSDN claims:
>>>>
>>>>     If the storage device is SCSI-compliant, the port driver attempts to
>>>>     extract the serial number from the optional Unit Serial Number page
>>>>     (page 0x80) of the VPD.
>>>>
>>>> Now I'm puzzled.
>>> A quick test with a Debian 12 VM in VirtualBox with many virtual
>>> controllers+drives shows the same problem:
>>> Entries in /dev/disk/by-id appear only for virtual disks behind emulated
>>> SATA and NVMe controllers, but not for SCSI and SAS controllers.
>>> A test with "smartctl -i ..." with SCSI/SAS devices doesn't print a serial
>>> number. In debug mode it prints "Vital Product Data (VPD) INQUIRY failed..."
>>> and other messages that suggest limited/buggy support of optional SCSI
>>> commands.
>>>
>>> If a Win11 PE (from install ISO) is run in same VM, the
>>> STORAGE_DEVICE_DESCRIPTOR only provides the serial number for SATA (NVMe
>>> drives not detected), but not for SCSI.
>>>
>>> Conclusion: The behavior of the current patch is compatible with Linux :-)
>> Ok, but with the DUID we have a workaround which makes it  work even
>> better than on Linux, so it would begreat if we used it, unless we find
>> out where the UUID in "\GLOBAL??\Disk{<UUID>} comes from...
>>
>> Given the size of the STORAGE_DEVICE_UNIQUE_IDENTIFIER struct, we could
>> even contemplate a 128 bit hash, just to be on the safe side.
> Kind of like this
>
> -  strcat (name, ioctl_buf + desc->SerialNumberOffset);
> +  /* Use SerialNumber in the first place, if available */
> +  if (desc->SerialNumberOffset && desc_buf[desc->SerialNumberOffset])
> +    strcat (name, desc_buf + desc->SerialNumberOffset);
> +  else /* Utilize the DUID as defined by MSDN to generate a hash */
> +    {
> +      union {
> +	unsigned __int128 all;
> +	struct {
> +	  unsigned long high;
> +	  unsigned long low;
> +	};
> +      } hash = { 0 };
> +
> +      for (ULONG i = 0; i < id->Size; ++i)
> +	hash.all = ioctl_buf[i] + (hash.all << 6) + (hash.all << 16) - hash.all;
> +      __small_sprintf (name + strlen (name), "%X%X", hash.high, hash.low);
> +    }
>

I agree and will provide a new patch soon.

Christian