Re: btt ndctl question

[Linda Knippers <linda.knippers@hpe.com>]

On 07/26/2016 05:31 PM, Dan Williams wrote:
> On Tue, Jul 26, 2016 at 2:24 PM, Verma, Vishal L
> <vishal.l.verma@intel.com> wrote:
>> On Tue, 2016-07-26 at 14:58 -0600, Vishal Verma wrote:
>>> On 07/26, Linda Knippers wrote:
>>>>
>>>> My system has 4 8G NVDIMMs and I have them configured in different
>>>> ways, as you can
>>>> see from the ndctl output:
>>>>
>>>> $ ndctl list
>>>> [
>>>>   {
>>>>     "dev":"namespace3.0",
>>>>     "mode":"raw",
>>>>     "size":8589934592,
>>>>     "blockdev":"pmem3"
>>>>   },
>>>>   {
>>>>     "dev":"namespace2.0",
>>>>     "mode":"memory",
>>>>     "size":8587837440,
>>>>     "uuid":"2567d762-68ae-486b-a6eb-2d3ab1b9dca9",
>>>>     "blockdev":"pmem2"
>>>>   },
>>>>   {
>>>>     "dev":"namespace1.0",
>>>>     "mode":"sector",
>>>>     "uuid":"44fb474e-7db8-4438-ad95-05ecb9f2075e",
>>>>     "sector_size":4096,
>>>>     "blockdev":"pmem1s"
>>>>   },
>>>>   {
>>>>     "dev":"namespace0.0",
>>>>     "mode":"memory",
>>>>     "size":8453619712,
>>>>     "uuid":"933ed54b-5b64-47f1-8409-c88f7c846522",
>>>>     "blockdev":"pmem0"
>>>>   }
>>>> ]
>>>>
>>>> The two memory namespaces have different sizes because one is --
>>>> map=dev and the other is --map=mem.
>>>> It would be nice if the map option was displayed but my question is
>>>> about the size value for the
>>>> btt device, or lack of one.
>>>>
>>>> All the namespaces show a size except for the btt.  The btt only
>>>> shows a sector size.  There
>>>> is no size value exposed by the btt sysfs information, which is
>>>> probably why it's not in ndctl.
>>>>
>>>> I know the size can be gotten from the block device but it looks
>>>> like an omission here.
>>>> Is this a bug or a feature?
>>>
>>> Probably an omission :)
>>> This patch should expose a size attribute in sysfs:
>>>
>>> $ cat /sys/bus/nd/devices/btt7.0/size
>>> 32440320
>>>
>>> I can look at the 'ndctl list' enabling too if this looks good.
>>>
>>> 8<------
>>>
>>> From fb119bf4380d1d65d82754e581bbd41161c2100f Mon Sep 17 00:00:00 2001
>>> From: Vishal Verma <vishal.l.verma@intel.com>
>>> Date: Tue, 26 Jul 2016 14:54:39 -0600
>>> Subject: [PATCH] nvdimm, btt: add a size attribute for BTTs
>>>
>>> To be consistent with other namespaces, expose a 'size' attribute for
>>> BTT devices also.
>>>
>>> Cc: Dan Williams <dan.j.williams@intel.com>
>>> Reported-by: Linda Knippers <linda.knippers@hpe.com>
>>> Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
>>> ---
>>>  drivers/nvdimm/btt.c      |  1 +
>>>  drivers/nvdimm/btt_devs.c | 15 +++++++++++++++
>>>  drivers/nvdimm/nd.h       |  1 +
>>>  3 files changed, 17 insertions(+)
>>>
>>> diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
>>> index 68a7c3c..71ce0dc 100644
>>> --- a/drivers/nvdimm/btt.c
>>> +++ b/drivers/nvdimm/btt.c
>>> @@ -1270,6 +1270,7 @@ static int btt_blk_init(struct btt *btt)
>>>               }
>>>       }
>>>       set_capacity(btt->btt_disk, btt->nlba * btt->sector_size >>
>>> 9);
>>> +     btt->nd_btt->size = btt->nlba * btt->sector_size;
>>
>> Blargh, I think I was a bit hasty; I think this should be:
>>
>> +       btt->nd_btt->size = btt->nlba * (u64)btt->sector_size;
>>
>> Right? (I always get bit by integer promotion rules...)
> 
> ...but at this point we're identical to what the block layer is
> reporting.  The other 'size' attributes are communicating the raw
> byte-aligned capacity of the namespace minus local driver overhead.

I tried Vishal's original patch and the btt is reporting a size of 8580472832
through sysfs.  It matches the capacity reported at boot time:

[   39.966252] pmem1s: detected capacity change from 0 to 8580472832
[   40.000069] pmem3: detected capacity change from 0 to 8589934592
[   40.112962] pmem2: detected capacity change from 0 to 8587837440
[   40.274013] pmem0: detected capacity change from 0 to 8453619712

For the other devices, the size reported by sysfs also matches what
is reported for the block device at boot time.

-- ljk

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