On 11/1/22 07:47, Bart Van Assche wrote:
> From ZBC-1:
> * RC BASIS = 0: The RETURNED LOGICAL BLOCK ADDRESS field indicates the
> highest LBA of a contiguous range of zones that are not sequential write
> required zones starting with the first zone.
> * RC BASIS = 1: The RETURNED LOGICAL BLOCK ADDRESS field indicates the LBA
> of the last logical block on the logical unit.
>
> The current scsi_debug READ CAPACITY response does not comply with the above
> if there are one or more sequential write required zones. SCSI initiators
> need a way to retrieve the largest valid LBA from SCSI devices. Reporting
> the largest valid LBA if there are one or more sequential zones requires to
> set the RC BASIS field in the READ CAPACITY response to one. Hence this
> patch.
>
> Cc: Douglas Gilbert <dgilbert@xxxxxxxxxxxx>
> Cc: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
> Suggested-by: Damien Le Moal <damien.lemoal@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
> ---
> drivers/scsi/scsi_debug.c | 4 ++++
> 1 file changed, 4 insertions(+)
>
> diff --git a/drivers/scsi/scsi_debug.c b/drivers/scsi/scsi_debug.c
> index 697fc57bc711..fec87296cf06 100644
> --- a/drivers/scsi/scsi_debug.c
> +++ b/drivers/scsi/scsi_debug.c
> @@ -1899,6 +1899,10 @@ static int resp_readcap16(struct scsi_cmnd *scp,
> arr[14] |= 0x40;
> }
>
> + /* Set RC BASIS = 1 for host-managed devices. */
No it is not necessarily set. It is up to the device vendor to choose if
RC_BASIS is set or not, based on the device implementation.
Applicability of RC = 0 or RC = 1 depends on the presence of conventional
zones. so:
1) If there are conventional zones, then using RC_BASIS = 1 or = 0 are
both OK with HM devices. In the case of RC_BASIS = 0, the host can issue a
report zones and get the device max lba from the report header (sd_zbc.c
does that).
2) If there are no conventional zones, then using RC_BASIS = 0 does not
make much sense, but nothing in the ZBC text prevent it either...
So we should refine this and maybe add an option to allow specifying rc
basis ?
> + if (devip->zmodel == BLK_ZONED_HM)
> + arr[12] |= 1 << 4;
> +
> arr[15] = sdebug_lowest_aligned & 0xff;
>
> if (have_dif_prot) {
--
Damien Le Moal
Western Digital Research
