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Date:   Mon, 1 Nov 2021 12:17:43 -0400
From:   Mike Snitzer <snitzer@redhat.com>
To:     Dan Williams <dan.j.williams@intel.com>
Cc:     Christoph Hellwig <hch@lst.de>, Ira Weiny <ira.weiny@intel.com>,
        device-mapper development <dm-devel@redhat.com>,
        linux-xfs <linux-xfs@vger.kernel.org>,
        Linux NVDIMM <nvdimm@lists.linux.dev>,
        linux-s390 <linux-s390@vger.kernel.org>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        linux-erofs@lists.ozlabs.org,
        linux-ext4 <linux-ext4@vger.kernel.org>,
        virtualization@lists.linux-foundation.org
Subject: Re: [PATCH 07/11] dax: remove dax_capable
Message-ID: <YYATJ+oDT15TD9Np@redhat.com>
References: <20211018044054.1779424-1-hch@lst.de>
 <20211018044054.1779424-8-hch@lst.de>
 <CAPcyv4gE8UXjQAe_6=BKFRCyLWNP_9CNxKFH---RpPnYfmBQLg@mail.gmail.com>
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On Wed, Oct 27 2021 at  8:16P -0400,
Dan Williams <dan.j.williams@intel.com> wrote:

> I am going to change the subject of this patch to:
> 
> dax: remove ->dax_supported()
> 
> On Sun, Oct 17, 2021 at 9:41 PM Christoph Hellwig <hch@lst.de> wrote:
> >
> 
> I'll add a bit more background to help others review this.
> 
> The ->dax_supported() operation arranges for a stack of devices to
> each answer the question "is dax operational". That request routes to
> generic_fsdax_supported() at last level device and that attempted an
> actual dax_direct_access() call and did some sanity checks. However,
> those sanity checks can be validated in other ways and with those
> removed the only question to answer is "has each block device driver
> in the stack performed dax_add_host()". That can be validated without
> a dax_operation. So, just open code the block size and dax_dev == NULL
> checks in the callers, and delete ->dax_supported().
> 
> Mike, let me know if you have any concerns.

Thanks for your additional background, it helped.


> 
> > Just open code the block size and dax_dev == NULL checks in the callers.
> >
> > Signed-off-by: Christoph Hellwig <hch@lst.de>
> > ---
> >  drivers/dax/super.c          | 36 ------------------------------------
> >  drivers/md/dm-table.c        | 22 +++++++++++-----------
> >  drivers/md/dm.c              | 21 ---------------------
> >  drivers/md/dm.h              |  4 ----
> >  drivers/nvdimm/pmem.c        |  1 -
> >  drivers/s390/block/dcssblk.c |  1 -
> >  fs/erofs/super.c             | 11 +++++++----
> >  fs/ext2/super.c              |  6 ++++--
> >  fs/ext4/super.c              |  9 ++++++---
> >  fs/xfs/xfs_super.c           | 21 ++++++++-------------
> >  include/linux/dax.h          | 14 --------------
> >  11 files changed, 36 insertions(+), 110 deletions(-)
> >
> > diff --git a/drivers/dax/super.c b/drivers/dax/super.c
> > index 482fe775324a4..803942586d1b6 100644
> > --- a/drivers/dax/super.c
> > +++ b/drivers/dax/super.c
> > @@ -108,42 +108,6 @@ struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
> >         return dax_dev;
> >  }
> >  EXPORT_SYMBOL_GPL(fs_dax_get_by_bdev);
> > -
> > -bool generic_fsdax_supported(struct dax_device *dax_dev,
> > -               struct block_device *bdev, int blocksize, sector_t start,
> > -               sector_t sectors)
> > -{
> > -       if (blocksize != PAGE_SIZE) {
> > -               pr_info("%pg: error: unsupported blocksize for dax\n", bdev);
> > -               return false;
> > -       }
> > -
> > -       if (!dax_dev) {
> > -               pr_debug("%pg: error: dax unsupported by block device\n", bdev);
> > -               return false;
> > -       }
> > -
> > -       return true;
> > -}
> > -EXPORT_SYMBOL_GPL(generic_fsdax_supported);
> > -
> > -bool dax_supported(struct dax_device *dax_dev, struct block_device *bdev,
> > -               int blocksize, sector_t start, sector_t len)
> > -{
> > -       bool ret = false;
> > -       int id;
> > -
> > -       if (!dax_dev)
> > -               return false;
> > -
> > -       id = dax_read_lock();
> > -       if (dax_alive(dax_dev) && dax_dev->ops->dax_supported)
> > -               ret = dax_dev->ops->dax_supported(dax_dev, bdev, blocksize,
> > -                                                 start, len);
> > -       dax_read_unlock(id);
> > -       return ret;
> > -}
> > -EXPORT_SYMBOL_GPL(dax_supported);
> >  #endif /* CONFIG_BLOCK && CONFIG_FS_DAX */
> >
> >  enum dax_device_flags {
> > diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> > index 1fa4d5582dca5..4ae671c2168ea 100644
> > --- a/drivers/md/dm-table.c
> > +++ b/drivers/md/dm-table.c
> > @@ -807,12 +807,14 @@ void dm_table_set_type(struct dm_table *t, enum dm_queue_mode type)
> >  EXPORT_SYMBOL_GPL(dm_table_set_type);
> >
> >  /* validate the dax capability of the target device span */
> > -int device_not_dax_capable(struct dm_target *ti, struct dm_dev *dev,
> > +static int device_not_dax_capable(struct dm_target *ti, struct dm_dev *dev,
> >                         sector_t start, sector_t len, void *data)
> >  {
> > -       int blocksize = *(int *) data;
> > +       if (dev->dax_dev)
> > +               return false;
> >
> > -       return !dax_supported(dev->dax_dev, dev->bdev, blocksize, start, len);
> > +       pr_debug("%pg: error: dax unsupported by block device\n", dev->bdev);

Would prefer the use of DMDEBUG() here (which doesn't need trailing \n)

But otherwise:
Acked-by: Mike Snitzer <snitzer@redhat.com>