Re: [PATCH 1/5] sd: configure ZBC devices

[Bart Van Assche <bart.vanassche@sandisk.com>]

On 07/23/16 13:31, Hannes Reinecke wrote:
> On 07/22/2016 11:56 PM, Ewan D. Milne wrote:
>> On Tue, 2016-07-19 at 15:25 +0200, Hannes Reinecke wrote:
>>> For ZBC devices I/O must not cross zone boundaries, so setup
>>> the 'chunk_sectors' block queue setting to the zone size.
>>> This is only valid for REPORT ZONES SAME type 2 or 3;
>>> for other types the zone sizes might be different
>>> for individual zones. So issue a warning if the type is
>>> found to be different.
>>> Also the capacity might be different from the announced
>>> capacity, so adjust it as needed.
>>>
>>> Signed-off-by: Hannes Reinecke <hare@suse.com>
>>
>> ...
>>
>>> +static void sd_read_zones(struct scsi_disk *sdkp, unsigned char *buffer)
>>> +{
>>> +	int retval;
>>> +	unsigned char *desc;
>>> +	u32 rep_len;
>>> +	u8 same;
>>> +	u64 zone_len, lba;
>>> +
>>> +	if (sdkp->zoned != 1)
>>> +		/* Device managed, no special handling required */
>>> +		return;
>>> +
>>> +	retval = sd_zbc_report_zones(sdkp, buffer, SD_BUF_SIZE,
>>> +				     0, ZBC_ZONE_REPORTING_OPTION_ALL, false);
>>> +	if (retval < 0)
>>> +		return;
>>> +
>>> +	rep_len = get_unaligned_be32(&buffer[0]);
>>> +	if (rep_len < 64) {
>>> +		sd_printk(KERN_WARNING, sdkp,
>>> +			  "REPORT ZONES report invalid length %u\n",
>>> +			  rep_len);
>>> +		return;
>>> +	}
>>> +
>>> +	if (sdkp->rc_basis == 0) {
>>> +		/* The max_lba field is the capacity of a zoned device */
>>> +		lba = get_unaligned_be64(&buffer[8]);
>>> +		if (lba + 1 > sdkp->capacity) {
>>> +			sd_printk(KERN_WARNING, sdkp,
>>> +				  "Max LBA %zu (capacity %zu)\n",
>>> +				  (sector_t) lba + 1, sdkp->capacity);
>>> +			sdkp->capacity = lba + 1;
>>> +		}
>>> +	}
>>> +
>>> +	/*
>>> +	 * Adjust 'chunk_sectors' to the zone length if the device
>>> +	 * supports equal zone sizes.
>>> +	 */
>>> +	same = buffer[4] & 0xf;
>>> +	if (same == 0 || same > 3) {
>>> +		sd_printk(KERN_WARNING, sdkp,
>>> +			  "REPORT ZONES SAME type %d not supported\n", same);
>>> +		return;
>>> +	}
>>> +	/* Read the zone length from the first zone descriptor */
>>> +	desc = &buffer[64];
>>> +	zone_len = logical_to_sectors(sdkp->device,
>>> +				      get_unaligned_be64(&desc[8]));
>>> +	blk_queue_chunk_sectors(sdkp->disk->queue, zone_len);
>>> +}
>>> +
>>
>> So, blk_queue_chunk_sectors() has:
>>
>> void blk_queue_chunk_sectors(struct request_queue *q, unsigned int chunk_sectors)
>> {
>>         BUG_ON(!is_power_of_2(chunk_sectors));
>>         q->limits.chunk_sectors = chunk_sectors;
>> }
>>
>> and it seems like if some device reports a non-power-of-2 zone_len then we
>> will BUG_ON().  Probably would be better if we reported an error instead?
>>
> The ZBC spec mandates that the zone size must be a power of 2.
> So I don't have problems with triggering a BUG_ON for non-compliant
> drives.

Triggering BUG_ON() if zone_len is not a power of two is completely 
unacceptable. No matter what zone information a ZBC drive exports that 
shouldn't result in a kernel oops.

Bart.