Re: [PATCH] BTT: Change nd_btt_arena_is_valid() to verify UUID

[Linda Knippers]

On 1/12/2016 11:38 AM, Dan Williams wrote:
> On Tue, Jan 12, 2016 at 7:02 AM, Toshi Kani <toshi.kani@xxxxxxx> wrote:
>> On Fri, 2015-12-18 at 14:23 -0800, Dan Williams wrote:
>>> On Fri, Dec 18, 2015 at 10:52 AM, Toshi Kani <toshi.kani@xxxxxxx> wrote:
>>>> On Fri, 2015-12-18 at 09:54 -0800, Dan Williams wrote:
>>>>> On Fri, Dec 18, 2015 at 7:15 AM, Toshi Kani <toshi.kani@xxxxxxx>
>>>>> wrote:
>>>>>> On Fri, 2015-12-18 at 01:34 -0700, Vishal Verma wrote:
>>>>>>> Also, I wonder if this problem is solved by using libndctl to
>>>>>>> manage
>>>>>>> BTTs.
>>>>>>
>>>>>> I have not tested with libndctl yet, but I think our bind/unbind
>>>>>> scripts do the same procedures.
>>>>>
>>>>> We loop through all combinations of sector size in our unit test.  If
>>>>> you want to change the sector size the expectation is that the
>>>>> namespace is destroyed and fully re-created, especially due to the
>>>>> fact that changing sector size invalidates all data on the namespace.
>>>>>
>>>>> See: https://github.com/pmem/ndctl/blob/master/lib/test-libndctl.c
>>>>
>>>> The parent_uuid is not set on our NVDIMM-N systems.  I do not see
>>>> 'uuid' file under sysfs 'namespaceX.X' per namespace_visible(), either.
>>>> This concept of creating/destroying a namespace is a bit foreign to us
>>>> since we've never needed to do.  Can you elaborate how it's supposed to
>>>> work for NVDIMM-N?
>>>>
>>>
>>> Ugh, yes.  An oversight on my part, let me give this some thought.
>>> Whatever we decide, I want the libndctl api to be identical for the
>>> two cases.
>>>
>>> I expect the simplest option is to have
>>> ndctl_namespace_disable_invalidate() destroy the btt-info block in the
>>> NVDIMM-N case.
>>
>> Do you have any update on this?  If we are going to use ndctl to address
>> this issue, does it mean that we will have to use ndctl to manage BTT?
> 
> This is my current proposal:
> 
> https://github.com/pmem/ndctl/blob/pending/Documentation/ndctl-create-namespace.txt

I don't really like "safe" as a mode choice.  The others are "memory" and "raw".
Could the one using the BTT be "sector" or "atomic" or "btt" or something other
than "safe"?  Using "safe" implies that the others aren't safe, but they are if
you use them for their intended purpose and know what you're doing.

-- ljk

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