dax: move the partition alignment check into fs_dax_get_by_bdev

fs_dax_get_by_bdev is the primary interface to find a dax device for a
block device, so move the partition alignment check there instead of
wiring it up through ->dax_supported.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Dan Williams <dan.j.williams@intel.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20211129102203.2243509-7-hch@lst.deSigned-off-by: Dan Williams <dan.j.williams@intel.com>

drivers/dax/super.c

@@ -92,6 +92,12 @@ struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
 	if (!blk_queue_dax(bdev->bd_disk->queue))
 		return NULL;
 
+	if ((get_start_sect(bdev) * SECTOR_SIZE) % PAGE_SIZE ||
+	    (bdev_nr_sectors(bdev) * SECTOR_SIZE) % PAGE_SIZE) {
+		pr_info("%pg: error: unaligned partition for dax\n", bdev);
+		return NULL;
+	}
+
 	id = dax_read_lock();
 	dax_dev = xa_load(&dax_hosts, (unsigned long)bdev->bd_disk);
 	if (!dax_dev || !dax_alive(dax_dev) || !igrab(&dax_dev->inode))
@@ -106,10 +112,6 @@ bool generic_fsdax_supported(struct dax_device *dax_dev,
 		struct block_device *bdev, int blocksize, sector_t start,
 		sector_t sectors)
 {
-	pgoff_t pgoff, pgoff_end;
-	sector_t last_page;
-	int err;
-
 	if (blocksize != PAGE_SIZE) {
 		pr_info("%pg: error: unsupported blocksize for dax\n", bdev);
 		return false;
@@ -120,19 +122,6 @@ bool generic_fsdax_supported(struct dax_device *dax_dev,
 		return false;
 	}
 
-	err = bdev_dax_pgoff(bdev, start, PAGE_SIZE, &pgoff);
-	if (err) {
-		pr_info("%pg: error: unaligned partition for dax\n", bdev);
-		return false;
-	}
-
-	last_page = PFN_DOWN((start + sectors - 1) * 512) * PAGE_SIZE / 512;
-	err = bdev_dax_pgoff(bdev, last_page, PAGE_SIZE, &pgoff_end);
-	if (err) {
-		pr_info("%pg: error: unaligned partition for dax\n", bdev);
-		return false;
-	}
-
 	return true;
 }
 EXPORT_SYMBOL_GPL(generic_fsdax_supported);