linux-kernel - [PATCH 3/6] folio: Add a function to get the host inode for a folio

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Message-ID: <162981151155.1901565.7010079316994382707.stgit@warthog.procyon.org.uk>
Date:   Tue, 24 Aug 2021 14:25:11 +0100
From:   David Howells <dhowells@...hat.com>
To:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc:     dhowells@...hat.com, Jeff Layton <jlayton@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-cachefs@...hat.com,
        linux-afs@...ts.infradead.org, linux-nfs@...r.kernel.org,
        linux-cifs@...r.kernel.org, ceph-devel@...r.kernel.org,
        v9fs-developer@...ts.sourceforge.net, devel@...ts.orangefs.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: [PATCH 3/6] folio: Add a function to get the host inode for a folio

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

Signed-off-by: David Howells <dhowells@...hat.com>
---

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

diff --git a/include/linux/pagemap.h b/include/linux/pagemap.h
index c8d336e62177..115b4f831e7d 100644
--- a/include/linux/pagemap.h
+++ b/include/linux/pagemap.h
@@ -203,6 +203,20 @@ 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 is hosting
+ * 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_file_mapping(folio)->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 86b90173baf8..f750946d11f7 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2918,7 +2918,7 @@ 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);