[PATCH v3 4/6] folio: Add a function to get the host inode for a folio

David Howells
2021-11-02T08:31:19Z

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

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

Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/YST8OcVNy02Rivbm@casper.infradead.org/ [1]
Link: https://lore.kernel.org/r/162880453171.3369675.3704943108660112470.stgit@warthog.procyon.org.uk/ # rfc
Link: https://lore.kernel.org/r/162981151155.1901565.7010079316994382707.stgit@warthog.procyon.org.uk/
Link: https://lore.kernel.org/r/163005744370.2472992.18324470937328925723.stgit@warthog.procyon.org.uk/ # v2
---

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 569302e4defe..fc4b7fcf4cc5 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->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 9c64490171e0..c4d2414a92dd 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -2960,7 +2960,7 @@ 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);