dax: introduce dax_direct_access()

Replace bdev_direct_access() with dax_direct_access() that uses
dax_device and dax_operations instead of a block_device and
block_device_operations for dax. Once all consumers of the old api have
been converted bdev_direct_access() will be deleted.

Given that block device partitioning decisions can cause dax page
alignment constraints to be violated this also introduces the
bdev_dax_pgoff() helper. It handles calculating a logical pgoff relative
to the dax_device and also checks for page alignment.

Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 39 insertions, 0 deletions

diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 1a58542ee8fd..465dcd7317d5 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -65,6 +65,45 @@ struct dax_device {
         const struct dax_operations *ops;
 };
 
+/**
+ * dax_direct_access() - translate a device pgoff to an absolute pfn
+ * @dax_dev: a dax_device instance representing the logical memory range
+ * @pgoff: offset in pages from the start of the device to translate
+ * @nr_pages: number of consecutive pages caller can handle relative to @pfn
+ * @kaddr: output parameter that returns a virtual address mapping of pfn
+ * @pfn: output parameter that returns an absolute pfn translation of @pgoff
+ *
+ * Return: negative errno if an error occurs, otherwise the number of
+ * pages accessible at the device relative @pgoff.
+ */
+long dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff, long nr_pages,
+                void **kaddr, pfn_t *pfn)
+{
+        long avail;
+
+        /*
+         * The device driver is allowed to sleep, in order to make the
+         * memory directly accessible.
+         */
+        might_sleep();
+
+        if (!dax_dev)
+                return -EOPNOTSUPP;
+
+        if (!dax_alive(dax_dev))
+                return -ENXIO;
+
+        if (nr_pages < 0)
+                return nr_pages;
+
+        avail = dax_dev->ops->direct_access(dax_dev, pgoff, nr_pages,
+                        kaddr, pfn);
+        if (!avail)
+                return -ERANGE;
+        return min(avail, nr_pages);
+}
+EXPORT_SYMBOL_GPL(dax_direct_access);
+
 bool dax_alive(struct dax_device *dax_dev)
 {
         lockdep_assert_held(&dax_srcu);