Re: [PATCH v2 0/1] MR7747: ntdll: Guess optical disc type based on data size.

[Alex Henrie (＠alexhenrie)]

On Fri May 23 04:23:45 2025 +0000, Alexandre Julliard wrote:
> > There is probably some tiny DVD somewhere in the world that will still
> > be misdetected, but I'm not sure that issuing SCSI commands to the drive
> > to try to determine the disc type would be any more reliable.
> > To support an app that is most likely going to issue DVD ioctls,
> > checking by using a DVD ioctl seems preferable.
> > Linux has only three [DVD ioctls](https://docs.kernel.org/userspace-api/ioctl/cdrom.html): DVD_READ_STRUCT, DVD_WRITE_STRUCT, and DVD_AUTH. It has no blu-ray ioctls. Of the three DVD ioctls, only DVD_READ_STRUCT would be suitable for disc type detection.

DVD_READ_STRUCT can read five kinds of information: DVD_STRUCT_PHYSICAL, DVD_STRUCT_COPYRIGHT, DVD_STRUCT_DISCKEY, DVD_STRUCT_BCA, and DVD_STRUCT_MANUFACT. Of those five, only DVD_STRUCT_PHYSICAL would be suitable for disc type detection.

At least on my LG WH16NS40 drive, DVD_STRUCT_PHYSICAL succeeds when there is a DVD in the drive, but it fails when there is a CD or a blu-ray in the drive. That means that we could use DVD_STRUCT_PHYSICAL to accurately detect whether there is a DVD in the drive, but we would still need another way to detect blu-rays.

Is there another ioctl that you had in mind, or something else that I missed? Do you want to try DVD_STRUCT_PHYSICAL first and fall back to guessing based on the data size if it fails? Please let me know how to proceed.

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https://gitlab.winehq.org/wine/wine/-/merge_requests/7747#note_104292