swap: rework map_swap_page() again

Seems that page_io.c doesn't really need to know that page_private(page)
is the swp_entry 'val'.  Rework map_swap_page() to do what its name says
and map a page to a page offset in the swap space.

The only other caller of map_swap_page() is internal to mm/swapfile.c and
it does want to map a swap entry to the 'sector'.  So rename
map_swap_page() to map_swap_entry(), make it 'static' and and implement
map_swap_page() as a wrapper around that.

Signed-off-by: Lee Schermerhorn <lee.schermerhorn@hp.com>
Cc: Hugh Dickins <hugh.dickins@tiscali.co.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 16 insertions, 4 deletions

diff --git a/mm/swapfile.c b/mm/swapfile.c
index 58bec660016..d5eb2e85600 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -38,6 +38,7 @@
 static bool swap_count_continued(struct swap_info_struct *, pgoff_t,
                                  unsigned char);
 static void free_swap_count_continuations(struct swap_info_struct *);
+static sector_t map_swap_entry(swp_entry_t, struct block_device**);
 
 static DEFINE_SPINLOCK(swap_lock);
 static unsigned int nr_swapfiles;
@@ -782,7 +783,7 @@ sector_t swapdev_block(int type, pgoff_t offset)
                 return 0;
         if (!(swap_info[type]->flags & SWP_WRITEOK))
                 return 0;
-        return map_swap_page(swp_entry(type, offset), &bdev);
+        return map_swap_entry(swp_entry(type, offset), &bdev);
 }
 
 /*
@@ -1249,10 +1250,11 @@ static void drain_mmlist(void)
 
 /*
  * Use this swapdev's extent info to locate the (PAGE_SIZE) block which
- * corresponds to page offset `offset'.  Note that the type of this function
- * is sector_t, but it returns page offset into the bdev, not sector offset.
+ * corresponds to page offset for the specified swap entry.
+ * Note that the type of this function is sector_t, but it returns page offset
+ * into the bdev, not sector offset.
  */
-sector_t map_swap_page(swp_entry_t entry, struct block_device **bdev)
+static sector_t map_swap_entry(swp_entry_t entry, struct block_device **bdev)
 {
         struct swap_info_struct *sis;
         struct swap_extent *start_se;
@@ -1281,6 +1283,16 @@ sector_t map_swap_page(swp_entry_t entry, struct block_device **bdev)
 }
 
 /*
+ * Returns the page offset into bdev for the specified page's swap entry.
+ */
+sector_t map_swap_page(struct page *page, struct block_device **bdev)
+{
+        swp_entry_t entry;
+        entry.val = page_private(page);
+        return map_swap_entry(entry, bdev);
+}
+
+/*
  * Free all of a swapdev's extent information
  */
 static void destroy_swap_extents(struct swap_info_struct *sis)