On Wed, Oct 27 2021 at  8:16P -0400,
Dan Williams [off-list ref] 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 [off-list ref] wrote:

quoted

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.

quoted

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 <redacted>