[PATCH 1/6] dax: Define a helper dax_pgoff() which takes in dax_offset as argument

[Vivek Goyal <vgoyal@redhat.com>]

Create a new helper dax_pgoff() which will replace bdev_dax_pgoff(). Difference
between two is that dax_pgoff() takes in "sector_t dax_offset" as an argument
instead of "struct block_device".

dax_offset specifies any offset into dax device which should be added to
sector while calculating pgoff.

Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
---
 drivers/dax/super.c | 12 ++++++++++++
 include/linux/dax.h |  1 +
 2 files changed, 13 insertions(+)

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 0aa4b6bc5101..e9daa30e4250 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -56,6 +56,18 @@ int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
 }
 EXPORT_SYMBOL(bdev_dax_pgoff);
 
+int dax_pgoff(sector_t dax_offset, sector_t sector, size_t size, pgoff_t *pgoff)
+{
+	phys_addr_t phys_off = (dax_offset + sector) * 512;
+
+	if (pgoff)
+		*pgoff = PHYS_PFN(phys_off);
+	if (phys_off % PAGE_SIZE || size % PAGE_SIZE)
+		return -EINVAL;
+	return 0;
+}
+EXPORT_SYMBOL(dax_pgoff);
+
 #if IS_ENABLED(CONFIG_FS_DAX)
 struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
 {
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 328c2dbb4409..5101a4b5c1f9 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -111,6 +111,7 @@ static inline bool daxdev_mapping_supported(struct vm_area_struct *vma,
 
 struct writeback_control;
 int bdev_dax_pgoff(struct block_device *, sector_t, size_t, pgoff_t *pgoff);
+int dax_pgoff(sector_t dax_offset, sector_t, size_t, pgoff_t *pgoff);
 #if IS_ENABLED(CONFIG_FS_DAX)
 bool __bdev_dax_supported(struct block_device *bdev, int blocksize);
 static inline bool bdev_dax_supported(struct block_device *bdev, int blocksize)
-- 
2.20.1
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