Re: [PATCH v2 3/5] ata: libata-scsi: route non-zero LUN commands for multi-LUN ATAPI

[Hannes Reinecke <hare@suse.de>]

On 4/20/26 14:23, Phil Pemberton wrote:
> Two changes are required to route commands to ATAPI LUNs other than 0:
> 
> 1. __ata_scsi_find_dev():  The existing code rejects any scsi_device
>     with a non-zero LUN, returning NULL and dropping the command on
>     the floor.  Relax both the PMP and non-PMP branches to allow
>     non-zero LUNs through when the underlying ata_device is ATAPI
>     class, since ATAPI devices can legitimately expose multiple LUNs.
> 
> 2. atapi_xlat():  Older ATAPI devices (SCSI-2 era) expect the LUN in
>     CDB byte 1 bits 7:5 rather than relying on transport-level LUN
>     addressing.  Encode scmd->device->lun into those bits, preserving
>     the existing command-specific bits in 4:0.  This is required by
>     both the Panasonic PD/CD combos and Nakamichi CD changers.
> 
> Signed-off-by: Phil Pemberton <philpem@philpem.me.uk>
> ---
>   drivers/ata/libata-scsi.c | 17 +++++++++++++++--
>   1 file changed, 15 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
> index 317883bac25f..4e88ae7d94c3 100644
> --- a/drivers/ata/libata-scsi.c
> +++ b/drivers/ata/libata-scsi.c
> @@ -2951,6 +2951,11 @@ static unsigned int atapi_xlat(struct ata_queued_cmd *qc)
>   	memset(qc->cdb, 0, dev->cdb_len);
>   	memcpy(qc->cdb, scmd->cmnd, scmd->cmd_len);
>   
> +	/* SCSI-2 CDB LUN encoding: bits 7:5 of byte 1 */
> +	if (scmd->device->lun < 8)
> +		qc->cdb[1] = (qc->cdb[1] & 0x1f) |
> +			      ((u8)scmd->device->lun << 5);
> +

Hmm. And what happens when scmd->device->lun is _greater_ than 7?
We surely should abort that command, shouldn't we?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@suse.de                                +49 911 74053 688
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