[dm-devel] [PATCH v3 09/11] block: Expose queue nr_zones in sysfs

[Hannes Reinecke]

On 10/12/18 9:55 AM, Damien Le Moal wrote:
> On 2018/10/12 16:41, Hannes Reinecke wrote:
>> On 10/12/18 4:30 AM, Damien Le Moal wrote:
>>> Expose through sysfs the nr_zones field of struct request_queue.
>>> Exposing this value helps in debugging disk issues as well as
>>> facilitating scripts based use of the disk (e.g. blktests).
>>>
>>> For zoned block devices, the nr_zones field indicates the total number
>>> of zones of the device calculated using the known disk capacity and
>>> zone size. This number of zones is always 0 for regular block devices.
>>>
>>> Since nr_zones is defined conditionally with CONFIG_BLK_DEV_ZONED,
>>> introduce the blk_queue_nr_zones() function to return the correct value
>>> for any device, regardless if CONFIG_BLK_DEV_ZONED is set.
>>>
>>> Signed-off-by: Damien Le Moal <damien.lemoal at wdc.com>
>>> ---
>>>    block/blk-sysfs.c      | 11 +++++++++++
>>>    include/linux/blkdev.h | 10 ++++++++++
>>>    2 files changed, 21 insertions(+)
>>>
>>> diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
>>> index 3772671cf2bc..92be8092ca4f 100644
>>> --- a/block/blk-sysfs.c
>>> +++ b/block/blk-sysfs.c
>>> @@ -300,6 +300,11 @@ static ssize_t queue_zoned_show(struct request_queue *q, char *page)
>>>    	}
>>>    }
>>>    
>>> +static ssize_t queue_nr_zones_show(struct request_queue *q, char *page)
>>> +{
>>> +	return queue_var_show(blk_queue_nr_zones(q), page);
>>> +}
>>> +
>>>    static ssize_t queue_nomerges_show(struct request_queue *q, char *page)
>>>    {
>>>    	return queue_var_show((blk_queue_nomerges(q) << 1) |
>>> @@ -637,6 +642,11 @@ static struct queue_sysfs_entry queue_zoned_entry = {
>>>    	.show = queue_zoned_show,
>>>    };
>>>    
>>> +static struct queue_sysfs_entry queue_nr_zones_entry = {
>>> +	.attr = {.name = "nr_zones", .mode = 0444 },
>>> +	.show = queue_nr_zones_show,
>>> +};
>>> +
>>>    static struct queue_sysfs_entry queue_nomerges_entry = {
>>>    	.attr = {.name = "nomerges", .mode = 0644 },
>>>    	.show = queue_nomerges_show,
>>> @@ -727,6 +737,7 @@ static struct attribute *default_attrs[] = {
>>>    	&queue_write_zeroes_max_entry.attr,
>>>    	&queue_nonrot_entry.attr,
>>>    	&queue_zoned_entry.attr,
>>> +	&queue_nr_zones_entry.attr,
>>>    	&queue_nomerges_entry.attr,
>>>    	&queue_rq_affinity_entry.attr,
>>>    	&queue_iostats_entry.attr,
>>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>>> index c24969b1741b..879753b10263 100644
>>> --- a/include/linux/blkdev.h
>>> +++ b/include/linux/blkdev.h
>>> @@ -804,6 +804,11 @@ static inline unsigned int blk_queue_zone_sectors(struct request_queue *q)
>>>    }
>>>    
>>>    #ifdef CONFIG_BLK_DEV_ZONED
>>> +static inline unsigned int blk_queue_nr_zones(struct request_queue *q)
>>> +{
>>> +	return blk_queue_is_zoned(q) ? q->nr_zones : 0;
>>> +}
>>> +
>>>    static inline unsigned int blk_queue_zone_no(struct request_queue *q,
>>>    					     sector_t sector)
>>>    {
>>> @@ -819,6 +824,11 @@ static inline bool blk_queue_zone_is_seq(struct request_queue *q,
>>>    		return false;
>>>    	return test_bit(blk_queue_zone_no(q, sector), q->seq_zones_bitmap);
>>>    }
>>> +#else /* CONFIG_BLK_DEV_ZONED */
>>> +static inline unsigned int blk_queue_nr_zones(struct request_queue *q)
>>> +{
>>> +	return 0;
>>> +}
>>>    #endif /* CONFIG_BLK_DEV_ZONED */
>>>    
>>>    static inline bool rq_is_sync(struct request *rq)
>>>
>> Actually, we should be checking whether we can't blank out this
>> attribute via the is_visible mechanism; after all, not every block
>> device is zoned, and those which are not have no need of the attribute...
> 
> Yes we could. But it is somewhat the same as drives that do not support trim:
> they get max_discard_sectors to 0. The attribute says "not supported because the
> value is 0". I followed the same principle for nr_zones: value of 0 says "no
> zones", hopefully in sync with "zoned" saying "none". And if these 2 are not in
> sync as such, then we have a defective drive or a bug. So actually always having
> nr_zones is useful I think.
> 
> But I can make it invisible for regular disks if you insist :)
> 
I don't mind; but then I might be zbc-biased already.
Leave up to the maintainers to decide.
Hence:

Reviewed-by: Hannes Reinecke <hare at suse.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare at suse.de			               +49 911 74053 688
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