[RFC PATCH 07/10] fs/dax: Create function dax_mapping_is_dax()

[ira.weiny@intel.com]

From: Ira Weiny <ira.weiny@intel.com>

In order to support longterm lease breaking operations.  Lease break
code in the file systems need to know if a mapping is DAX.

Split out the logic to determine if a mapping is DAX and export it.
---
 fs/dax.c            | 23 ++++++++++++++++-------
 include/linux/dax.h |  6 ++++++
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index ca0671d55aa6..c3a932235e88 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -551,6 +551,21 @@ static void *grab_mapping_entry(struct xa_state *xas,
 	return xa_mk_internal(VM_FAULT_FALLBACK);
 }
 
+bool dax_mapping_is_dax(struct address_space *mapping)
+{
+	/*
+	 * In the 'limited' case get_user_pages() for dax is disabled.
+	 */
+	if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
+		return false;
+
+	if (!dax_mapping(mapping) || !mapping_mapped(mapping))
+		return false;
+
+	return true;
+}
+EXPORT_SYMBOL_GPL(dax_mapping_is_dax);
+
 /**
  * dax_layout_busy_page - find first pinned page in @mapping
  * @mapping: address space to scan for a page with ref count > 1
@@ -573,13 +588,7 @@ struct page *dax_layout_busy_page(struct address_space *mapping)
 	unsigned int scanned = 0;
 	struct page *page = NULL;
 
-	/*
-	 * In the 'limited' case get_user_pages() for dax is disabled.
-	 */
-	if (IS_ENABLED(CONFIG_FS_DAX_LIMITED))
-		return NULL;
-
-	if (!dax_mapping(mapping) || !mapping_mapped(mapping))
+	if (!dax_mapping_is_dax(mapping))
 		return NULL;
 
 	/*
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 0dd316a74a29..78fea21b990e 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -89,6 +89,7 @@ struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev);
 int dax_writeback_mapping_range(struct address_space *mapping,
 		struct block_device *bdev, struct writeback_control *wbc);
 
+bool dax_mapping_is_dax(struct address_space *mapping);
 struct page *dax_layout_busy_page(struct address_space *mapping);
 dax_entry_t dax_lock_page(struct page *page);
 void dax_unlock_page(struct page *page, dax_entry_t cookie);
@@ -113,6 +114,11 @@ static inline struct dax_device *fs_dax_get_by_bdev(struct block_device *bdev)
 	return NULL;
 }
 
+bool dax_mapping_is_dax(struct address_space *mapping)
+{
+	return false;
+}
+
 static inline struct page *dax_layout_busy_page(struct address_space *mapping)
 {
 	return NULL;
-- 
2.20.1