[v4,2/5] folio: Add a function to get the host inode for a folio

Commit Message

David Howells Nov. 9, 2021, 9:27 p.m. UTC

Add a convenience function, folio_inode() that will get the host inode from
a folio's mapping.

Changes:
 ver #3:
  - Fix mistake in function description[2].
 ver #2:
  - Fix contradiction between doc and implementation by disallowing use
    with swap caches[1].

Signed-off-by: David Howells <[e-mail]>
Reviewed-by: Matthew Wilcox (Oracle) <[e-mail]>
Tested-by: Jeff Layton <[e-mail]>
Tested-by: Dominique Martinet <[e-mail]>
Tested-by: [e-mail]
Link: https://lore.kernel.org/r/[e-mail]/ [1]
Link: https://lore.kernel.org/r/[e-mail]/ [2]
Link: https://lore.kernel.org/r/[e-mail]/ # rfc
Link: https://lore.kernel.org/r/[e-mail]/
Link: https://lore.kernel.org/r/[e-mail]/ # v2
Link: https://lore.kernel.org/r/[e-mail]/ # v3
---

 include/linux/pagemap.h |   14 ++++++++++++++
 mm/page-writeback.c     |    2 +-
 2 files changed, 15 insertions(+), 1 deletion(-)

Patch

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index 1f560aecd9b5..1a0c646eb6ff 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -253,6 +253,20 @@  static inline struct address_space *page_mapping_file(struct page *page)
 	return folio_mapping(folio);
 }
 
+/**
+ * folio_inode - Get the host inode for this folio.
+ * @folio: The folio.
+ *
+ * For folios which are in the page cache, return the inode that this folio
+ * belongs to.
+ *
+ * Do not call this for folios which aren't in the page cache.
+ */
+static inline struct inode *folio_inode(struct folio *folio)
+{
+	return folio->mapping->host;
+}
+
 static inline bool page_cache_add_speculative(struct page *page, int count)
 {
 	VM_BUG_ON_PAGE(PageTail(page), page);
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 2d498bb62248..a613f8ef6a02 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2967,7 +2967,7 @@  EXPORT_SYMBOL_GPL(folio_wait_writeback_killable);
  */
 void folio_wait_stable(struct folio *folio)
 {
-	if (folio->mapping->host->i_sb->s_iflags & SB_I_STABLE_WRITES)
+	if (folio_inode(folio)->i_sb->s_iflags & SB_I_STABLE_WRITES)
 		folio_wait_writeback(folio);
 }
 EXPORT_SYMBOL_GPL(folio_wait_stable);