[RFC 3/4] fs/buffer: add folio_create_empty_buffers helper

[Pankaj Raghav]

Folio version of create_empty_buffers(). This is required to convert
create_page_buffers() to create_folio_buffers() later in the series.

It removes several calls to compound_head() as it works directly on folio
compared to create_empty_buffers().

Signed-off-by: Pankaj Raghav <p.raghav@xxxxxxxxxxx>
---
 fs/buffer.c                 | 34 ++++++++++++++++++++++++++++++++++
 include/linux/buffer_head.h |  2 ++
 2 files changed, 36 insertions(+)

diff --git a/fs/buffer.c b/fs/buffer.c
index 0f9c2127543d..9e6a1a738fb5 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -1645,6 +1645,40 @@ void block_invalidate_folio(struct folio *folio, size_t offset, size_t length)
 }
 EXPORT_SYMBOL(block_invalidate_folio);
 
+/*
+ * We attach and possibly dirty the buffers atomically wrt
+ * block_dirty_folio() via private_lock.  try_to_free_buffers
+ * is already excluded via the folio lock.
+ */
+void folio_create_empty_buffers(struct folio *folio, unsigned long blocksize,
+				unsigned long b_state)
+{
+	struct buffer_head *bh, *head, *tail;
+
+	head = alloc_folio_buffers(folio, blocksize, true);
+	bh = head;
+	do {
+		bh->b_state |= b_state;
+		tail = bh;
+		bh = bh->b_this_page;
+	} while (bh);
+	tail->b_this_page = head;
+
+	spin_lock(&folio->mapping->private_lock);
+	if (folio_test_uptodate(folio) || folio_test_dirty(folio)) {
+		bh = head;
+		do {
+			if (folio_test_dirty(folio))
+				set_buffer_dirty(bh);
+			if (folio_test_uptodate(folio))
+				set_buffer_uptodate(bh);
+			bh = bh->b_this_page;
+		} while (bh != head);
+	}
+	folio_attach_private(folio, head);
+	spin_unlock(&folio->mapping->private_lock);
+}
+EXPORT_SYMBOL(folio_create_empty_buffers);
 
 /*
  * We attach and possibly dirty the buffers atomically wrt
diff --git a/include/linux/buffer_head.h b/include/linux/buffer_head.h
index d5a2ef9b4cdf..8afa91cbb8e2 100644
--- a/include/linux/buffer_head.h
+++ b/include/linux/buffer_head.h
@@ -203,6 +203,8 @@ struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
 		bool retry);
 void create_empty_buffers(struct page *, unsigned long,
 			unsigned long b_state);
+void folio_create_empty_buffers(struct folio *, unsigned long,
+				unsigned long b_state);
 void end_buffer_read_sync(struct buffer_head *bh, int uptodate);
 void end_buffer_write_sync(struct buffer_head *bh, int uptodate);
 void end_buffer_async_write(struct buffer_head *bh, int uptodate);
-- 
2.34.1