linux-kernel - Re: [PATCH v3 1/3] pmem: only set QUEUE_FLAG

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Message-ID: <20180626185830.GA7171@redhat.com>
Date:   Tue, 26 Jun 2018 14:58:30 -0400
From:   Mike Snitzer <snitzer@...hat.com>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Toshi Kani <toshi.kani@....com>,
        device-mapper development <dm-devel@...hat.com>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH v3 1/3] pmem: only set QUEUE_FLAG_DAX for fsdax mode

On Tue, Jun 26 2018 at  2:52pm -0400,
Dan Williams <dan.j.williams@...el.com> wrote:

> On Tue, Jun 26, 2018 at 10:59 AM, Ross Zwisler
> <ross.zwisler@...ux.intel.com> wrote:
> > QUEUE_FLAG_DAX is an indication that a given block device supports
> > filesystem DAX and should not be set for PMEM namespaces which are in "raw"
> > or "sector" modes.  These namespaces lack struct page and are prevented
> > from participating in filesystem DAX.
> >
> > Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
> > Suggested-by: Mike Snitzer <snitzer@...hat.com>
> > Cc: stable@...r.kernel.org
> 
> Why is this cc: stable? What is the user visible impact of this change
> especially given the requirement to validate QUEUE_FLAG_DAX with
> bdev_dax_supported()? Patch looks good, but it's just a cosmetic fixup
> afaics.

This isn't cosmetic when you consider that stacking up a DM device is
looking at this flag to determine whether a table does or does _not_
support DAX.

So this patch, in conjunction with the other changes in the series, is
certainly something I'd consider appropriate for stable.

Mike