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

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Date:   Thu, 3 Feb 2022 21:34:25 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jane Chu <jane.chu@...cle.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 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.