linux-kernel - Re: [PATCH] libnvdimm, region: sysfs trigger for nvdimm

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Date:   Mon, 24 Apr 2017 00:04:23 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Masayoshi Mizuma <m.mizuma@...fujitsu.com>
Cc:     "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        Linux ACPI <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] libnvdimm, region: sysfs trigger for nvdimm_flush()

On Sun, Apr 23, 2017 at 10:31 PM, Masayoshi Mizuma
<m.mizuma@...fujitsu.com> wrote:
> On Fri, 21 Apr 2017 16:48:57 -0700 Dan Williams wrote:
>> The nvdimm_flush() mechanism helps to reduce the impact of an ADR
>> (asynchronous-dimm-refresh) failure. The ADR mechanism handles flushing
>> platform WPQ (write-pending-queue) buffers when power is removed. The
>> nvdimm_flush() mechanism performs that same function on-demand.
>>
>> When a pmem namespace is associated with a block device, an
>> nvdimm_flush() is triggered with every block-layer REQ_FUA, or REQ_FLUSH
>> request. However, when a namespace is in device-dax mode, or namespaces
>> are disabled, userspace needs another path.
>>
>> The new 'flush' attribute is visible when it can be determined that the
>> interleave-set either does, or does not have DIMMs that expose WPQ-flush
>> addresses, "flush-hints" in ACPI NFIT terminology. It returns "1" and
>> flushes DIMMs, or returns "0" the flush operation is a platform nop.
>>
>> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
>> ---
>>  drivers/nvdimm/region_devs.c |   17 +++++++++++++++++
>>  1 file changed, 17 insertions(+)
>>
>> diff --git a/drivers/nvdimm/region_devs.c b/drivers/nvdimm/region_devs.c
>> index 8de5a04644a1..3495b4c23941 100644
>> --- a/drivers/nvdimm/region_devs.c
>> +++ b/drivers/nvdimm/region_devs.c
>> @@ -255,6 +255,19 @@ static ssize_t size_show(struct device *dev,
>>  }
>>  static DEVICE_ATTR_RO(size);
>>
>> +static ssize_t flush_show(struct device *dev,
>> +             struct device_attribute *attr, char *buf)
>> +{
>> +     struct nd_region *nd_region = to_nd_region(dev);
>> +
>> +     if (nvdimm_has_flush(nd_region)) {
>
> nvdimm_has_flush() also returns as -ENXIO, so
>
> if (nvdimm_has_flush(nd_region) == 1)

If it returns -ENXIO then region_visible() will hide the attribute.

>
>> +             nvdimm_flush(nd_region);
>> +             return sprintf(buf, "1\n");
>> +     }
>> +     return sprintf(buf, "0\n");
>> +}
>> +static DEVICE_ATTR_RO(flush);
>> +
>
> I think separating show and store is better because
> users may only check wheter the device has the flush capability or not.

Makes sense, I'll separate. Thanks for the review.