quoted

commenting out the error check after ata_dev_init_params() call in
ata_dev_read_id() function (libata-core.c), I got at least the device name.
The capacity is 0 so it doesn't work, obviously:

If you don't read the ID then it wouldn't.

I captured the IDENTIFY data from the virtual device. I'm not ATA guru but
looking at the data, there are zeros at many places where something should be.
That number starting at 0x78 looks like size of the array in sectors
(0x4C726C or 0x4C6C72 - the array is built from 2.5GB and 6.4GB drives).

The Ident data for the virtual device is fairly sparse but the specs
don't require a lot of the field are filled in and only the LBA really
matters.