[PATCH v2 12/30] dax: remove block device dependencies

[Vivek Goyal <vgoyal@redhat.com>]

From: Stefan Hajnoczi <stefanha@redhat.com>

Although struct dax_device itself is not tied to a block device, some
DAX code assumes there is a block device.  Make block devices optional
by allowing bdev to be NULL in commonly used DAX APIs.

When there is no block device:
 * Skip the partition offset calculation in bdev_dax_pgoff()
 * Skip the blkdev_issue_zeroout() optimization

Note that more block device assumptions remain but I haven't reach those
code paths yet.

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 drivers/dax/super.c | 3 ++-
 fs/dax.c            | 7 ++++++-
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 0a339b85133e..cb44ec663991 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -53,7 +53,8 @@ EXPORT_SYMBOL_GPL(dax_read_unlock);
 int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
 		pgoff_t *pgoff)
 {
-	phys_addr_t phys_off = (get_start_sect(bdev) + sector) * 512;
+	sector_t start_sect = bdev ? get_start_sect(bdev) : 0;
+	phys_addr_t phys_off = (start_sect + sector) * 512;
 
 	if (pgoff)
 		*pgoff = PHYS_PFN(phys_off);
diff --git a/fs/dax.c b/fs/dax.c
index e5e54da1715f..815bc32fd967 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1042,7 +1042,12 @@ static vm_fault_t dax_load_hole(struct xa_state *xas,
 static bool dax_range_is_aligned(struct block_device *bdev,
 				 unsigned int offset, unsigned int length)
 {
-	unsigned short sector_size = bdev_logical_block_size(bdev);
+	unsigned short sector_size;
+
+	if (!bdev)
+		return false;
+
+	sector_size = bdev_logical_block_size(bdev);
 
 	if (!IS_ALIGNED(offset, sector_size))
 		return false;
-- 
2.20.1