[PATCH 2/2] fs/dax: Make dax_layout_busy_page_range() static

[Kaitao Cheng <kaitao.cheng@linux.dev>]

From: Kaitao Cheng <chengkaitao@kylinos.cn>

dax_layout_busy_page_range() no longer has callers outside fs/dax.c.
Keeping the range helper exported unnecessarily exposes a low-level
implementation detail.

Make the helper static and remove its export and header definitions.

Also fix the stale dax_layout_busy_page_range() comment to match the
implementation.

Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
 fs/dax.c            | 18 ++++++++----------
 include/linux/dax.h |  6 ------
 2 files changed, 8 insertions(+), 16 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 1e19e4a354ce..c6ad9533aa54 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -770,24 +770,23 @@ static void *grab_mapping_entry(struct xa_state *xas,
 
 /**
  * dax_layout_busy_page_range - find first pinned page in @mapping
- * @mapping: address space to scan for a page with ref count > 1
+ * @mapping: address space to scan for a pinned page
  * @start: Starting offset. Page containing 'start' is included.
  * @end: End offset. Page containing 'end' is included. If 'end' is LLONG_MAX,
  *       pages from 'start' till the end of file are included.
  *
- * DAX requires ZONE_DEVICE mapped pages. These pages are never
- * 'onlined' to the page allocator so they are considered idle when
- * page->count == 1. A filesystem uses this interface to determine if
- * any page in the mapping is busy, i.e. for DMA, or other
- * get_user_pages() usages.
+ * DAX requires ZONE_DEVICE mapped pages. A page is considered busy when
+ * folio_ref_count(folio) exceeds folio_mapcount(folio). This helper is
+ * used to determine if any page in the mapping is busy, i.e. for DMA,
+ * or other get_user_pages() usages.
  *
  * It is expected that the filesystem is holding locks to block the
  * establishment of new mappings in this address_space. I.e. it expects
- * to be able to run unmap_mapping_range() and subsequently not race
+ * to be able to run unmap_mapping_pages() and subsequently not race
  * mapping_mapped() becoming true.
  */
-struct page *dax_layout_busy_page_range(struct address_space *mapping,
-					loff_t start, loff_t end)
+static struct page *dax_layout_busy_page_range(struct address_space *mapping,
+					       loff_t start, loff_t end)
 {
 	void *entry;
 	unsigned int scanned = 0;
@@ -839,7 +838,6 @@ struct page *dax_layout_busy_page_range(struct address_space *mapping,
 	xas_unlock_irq(&xas);
 	return page;
 }
-EXPORT_SYMBOL_GPL(dax_layout_busy_page_range);
 
 static int __dax_invalidate_entry(struct address_space *mapping,
 				  pgoff_t index, bool trunc)
diff --git a/include/linux/dax.h b/include/linux/dax.h
index 05e59e45a1c2..f2d47975d905 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -155,7 +155,6 @@ int dax_writeback_mapping_range(struct address_space *mapping,
 		struct dax_device *dax_dev, struct writeback_control *wbc);
 int dax_folio_reset_order(struct folio *folio);
 
-struct page *dax_layout_busy_page_range(struct address_space *mapping, loff_t start, loff_t end);
 dax_entry_t dax_lock_folio(struct folio *folio);
 void dax_unlock_folio(struct folio *folio, dax_entry_t cookie);
 dax_entry_t dax_lock_mapping_entry(struct address_space *mapping,
@@ -172,11 +171,6 @@ static inline int fs_dax_get(struct dax_device *dax_dev, void *holder,
 {
 	return -EOPNOTSUPP;
 }
-static inline struct page *dax_layout_busy_page_range(struct address_space *mapping, pgoff_t start, pgoff_t nr_pages)
-{
-	return NULL;
-}
-
 static inline int dax_writeback_mapping_range(struct address_space *mapping,
 		struct dax_device *dax_dev, struct writeback_control *wbc)
 {
-- 
2.50.1 (Apple Git-155)