dm-log-writes: add a log_writes_dax_pgoff helper

Add a helper to perform the entire remapping for DAX accesses.  This
helper open codes bdev_dax_pgoff given that the alignment checks have
already been done by the submitting file system and don't need to be
repeated.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Acked-by: NMike Snitzer <snitzer@redhat.com>
Reviewed-by: NDan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/r/20211129102203.2243509-11-hch@lst.deSigned-off-by: NDan Williams <dan.j.williams@intel.com>

drivers/md/dm-log-writes.c

@@ -947,17 +947,21 @@ static int log_dax(struct log_writes_c *lc, sector_t sector, size_t bytes,
 	return 0;
 }
 
+static struct dax_device *log_writes_dax_pgoff(struct dm_target *ti,
+		pgoff_t *pgoff)
+{
+	struct log_writes_c *lc = ti->private;
+
+	*pgoff += (get_start_sect(lc->dev->bdev) >> PAGE_SECTORS_SHIFT);
+	return lc->dev->dax_dev;
+}
+
 static long log_writes_dax_direct_access(struct dm_target *ti, pgoff_t pgoff,
 					 long nr_pages, void **kaddr, pfn_t *pfn)
 {
-	struct log_writes_c *lc = ti->private;
-	sector_t sector = pgoff * PAGE_SECTORS;
-	int ret;
+	struct dax_device *dax_dev = log_writes_dax_pgoff(ti, &pgoff);
 
-	ret = bdev_dax_pgoff(lc->dev->bdev, sector, nr_pages * PAGE_SIZE, &pgoff);
-	if (ret)
-		return ret;
-	return dax_direct_access(lc->dev->dax_dev, pgoff, nr_pages, kaddr, pfn);
+	return dax_direct_access(dax_dev, pgoff, nr_pages, kaddr, pfn);
 }
 
 static size_t log_writes_dax_copy_from_iter(struct dm_target *ti,
@@ -966,11 +970,9 @@ static size_t log_writes_dax_copy_from_iter(struct dm_target *ti,
 {
 	struct log_writes_c *lc = ti->private;
 	sector_t sector = pgoff * PAGE_SECTORS;
+	struct dax_device *dax_dev = log_writes_dax_pgoff(ti, &pgoff);
 	int err;
 
-	if (bdev_dax_pgoff(lc->dev->bdev, sector, ALIGN(bytes, PAGE_SIZE), &pgoff))
-		return 0;
-
 	/* Don't bother doing anything if logging has been disabled */
 	if (!lc->logging_enabled)
 		goto dax_copy;
@@ -981,34 +983,24 @@ static size_t log_writes_dax_copy_from_iter(struct dm_target *ti,
 		return 0;
 	}
 dax_copy:
-	return dax_copy_from_iter(lc->dev->dax_dev, pgoff, addr, bytes, i);
+	return dax_copy_from_iter(dax_dev, pgoff, addr, bytes, i);
 }
 
 static size_t log_writes_dax_copy_to_iter(struct dm_target *ti,
 					  pgoff_t pgoff, void *addr, size_t bytes,
 					  struct iov_iter *i)
 {
-	struct log_writes_c *lc = ti->private;
-	sector_t sector = pgoff * PAGE_SECTORS;
+	struct dax_device *dax_dev = log_writes_dax_pgoff(ti, &pgoff);
 
-	if (bdev_dax_pgoff(lc->dev->bdev, sector, ALIGN(bytes, PAGE_SIZE), &pgoff))
-		return 0;
-	return dax_copy_to_iter(lc->dev->dax_dev, pgoff, addr, bytes, i);
+	return dax_copy_to_iter(dax_dev, pgoff, addr, bytes, i);
 }
 
 static int log_writes_dax_zero_page_range(struct dm_target *ti, pgoff_t pgoff,
 					  size_t nr_pages)
 {
-	int ret;
-	struct log_writes_c *lc = ti->private;
-	sector_t sector = pgoff * PAGE_SECTORS;
+	struct dax_device *dax_dev = log_writes_dax_pgoff(ti, &pgoff);
 
-	ret = bdev_dax_pgoff(lc->dev->bdev, sector, nr_pages << PAGE_SHIFT,
-			     &pgoff);
-	if (ret)
-		return ret;
-	return dax_zero_page_range(lc->dev->dax_dev, pgoff,
-				   nr_pages << PAGE_SHIFT);
+	return dax_zero_page_range(dax_dev, pgoff, nr_pages << PAGE_SHIFT);
 }
 
 #else