Re: [ndctl PATCH] libndctl: Update nvdimm flags after inject-smart

[Vaibhav Jain <vaibhav@linux.ibm.com>]

Thanks for looking into this patch Dan

Dan Williams <dan.j.williams@intel.com> writes:

> On Tue, Jul 13, 2021 at 1:25 PM Vaibhav Jain <vaibhav@linux.ibm.com> wrote:
>>
>> Presently after performing a inject-smart the nvdimm flags reported are out
>> of date as shown below where no 'smart_notify' or 'flush_fail' flags were
>> reported even though they are set after injecting the smart error:
>>
>> $ sudo inject-smart -fU nmem0
>> [
>>   {
>>     "dev":"nmem0",
>>     "health":{
>>       "health_state":"fatal",
>>       "shutdown_state":"dirty",
>>       "shutdown_count":0
>>     }
>>   }
>> ]
>> $ sudo cat /sys/class/nd/ndctl0/device/nmem0/papr/flags
>> flush_fail smart_notify
>>
>> This happens because nvdimm flags are only parsed once during its probe and
>> not refreshed even after a inject-smart operation makes them out of
>> date. To fix this the patch adds a new export from libndctl named as
>> ndctl_refresh_dimm_flags() that can be called after inject-smart that
>> forces a refresh of nvdimm flags. This ensures that correct nvdimm flags
>> are reported after the inject-smart operation as shown below:
>>
>> $ sudo ndctl inject-smart -fU nmem0
>> [
>>   {
>>     "dev":"nmem0",
>>     "flag_failed_flush":true,
>>     "flag_smart_event":true,
>>     "health":{
>>       "health_state":"fatal",
>>       "shutdown_state":"dirty",
>>       "shutdown_count":0
>>     }
>>   }
>> ]
>>
>> The patch refactors populate_dimm_attributes() to move the nvdimm flags
>> parsing code to the newly introduced ndctl_refresh_dimm_flags()
>> export. Since reading nvdimm flags requires constructing path using
>> 'bus_prefix' which is only available during add_dimm(), the patch
>> introduces a new member 'struct ndctl_dimm.bus_prefix' to cache its
>> value. During ndctl_refresh_dimm_flags() the cached bus_prefix is used to
>> read the contents of the nvdimm flag file and pass it on to the appropriate
>> flag parsing function.
>
> I think this can be handled without needing an explicit
> ndctl_refresh_dimm_flags() api. Teach all the flag retrieval apis to
> check if the cached value has been invalidated and re-parse the flags.
> Then teach the inject-smart path to invalidate the cached copy of the
> flags.
>
Thanks for the suggestion. On the same line I think refreshing nvdimm
flags can also be done implicitly after a successful ndctl_cmd_submit()
call as that point we have interacted with the kernel_module which may
have triggered a nvdimm flags change.

Such a changeset would also be smaller compared to updating all flags
retrieval api's to invalidate and refresh nvdimm flags.

-- 
Cheers
~ Vaibhav