linux-kernel - Re: [PATCH v5 3/7] dm: make dm aware of target's DAXDEV

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Message-ID: <1ae40b1b-9d07-a69c-aed8-e6a6b63b1cc6@oracle.com>
Date:   Sun, 6 Feb 2022 08:27:23 +0000
From:   Jane Chu <jane.chu@...cle.com>
To:     Dan Williams <dan.j.williams@...el.com>
CC:     david <david@...morbit.com>, "Darrick J. Wong" <djwong@...nel.org>,
        Christoph Hellwig <hch@...radead.org>,
        Vishal L Verma <vishal.l.verma@...el.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        device-mapper development <dm-devel@...hat.com>,
        "Weiny, Ira" <ira.weiny@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        Vivek Goyal <vgoyal@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux NVDIMM <nvdimm@...ts.linux.dev>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>
Subject: Re: [PATCH v5 3/7] dm: make dm aware of target's DAXDEV_RECOVERY
 capability

On 2/3/2022 9:34 PM, Dan Williams wrote:
> On Fri, Jan 28, 2022 at 1:32 PM Jane Chu <jane.chu@...cle.com> wrote:
>>
>> If one of the MD raid participating target dax device supports
>> DAXDEV_RECOVERY, then it'll be declared on the whole that the
>> MD device is capable of DAXDEV_RECOVERY.
>> And only when the recovery process reaches to the target driver,
>> it becomes deterministic whether a certain dax address range
>> maybe recovered, or not.
>>
>> Signed-off-by: Jane Chu <jane.chu@...cle.com>
>> ---
>>   drivers/md/dm-table.c | 33 +++++++++++++++++++++++++++++++++
>>   1 file changed, 33 insertions(+)
>>
>> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
>> index e43096cfe9e2..8af8a81b6172 100644
>> --- a/drivers/md/dm-table.c
>> +++ b/drivers/md/dm-table.c
>> @@ -844,6 +844,36 @@ static bool dm_table_supports_dax(struct dm_table *t,
>>          return true;
>>   }
>>
>> +/* Check whether device is capable of dax poison recovery */
>> +static int device_poison_recovery_capable(struct dm_target *ti,
>> +       struct dm_dev *dev, sector_t start, sector_t len, void *data)
>> +{
>> +       if (!dev->dax_dev)
>> +               return false;
>> +       return dax_recovery_capable(dev->dax_dev);
> 
> Hmm it's not clear to me that dax_recovery_capable is necessary. If a
> dax_dev does not support recovery it can simply fail the
> dax_direct_access() call with the DAX_RECOVERY flag set.
> 
> So all DM needs to worry about is passing the new @flags parameter
> through the stack.

Yeah, given your idea about adding the .recovery_write to pgmap_ops, it 
wouldn't be needed.

thanks,
-jane