[PATCH 02/14] btrfs: extent_io: introduce a helper to grab an existing extent buffer from a page

[Qu Wenruo <wqu@suse.com>]

This patch will extract the code to grab an extent buffer from a page
into a helper, grab_extent_buffer_from_page().

This reduces one indent level, and provides the work place for later
expansion for subapge support.

Signed-off-by: Qu Wenruo <wqu@suse.com>
---
 fs/btrfs/extent_io.c | 60 ++++++++++++++++++++++++++------------------
 1 file changed, 36 insertions(+), 24 deletions(-)

diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 55115f485d09..759d2f2292ed 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -5249,6 +5249,36 @@ struct extent_buffer *alloc_test_extent_buffer(struct btrfs_fs_info *fs_info,
 }
 #endif
 
+static struct extent_buffer *grab_extent_buffer_from_page(struct page *page)
+{
+	struct extent_buffer *exists;
+
+	/* Page not yet attached to an extent buffer */
+	if (!PagePrivate(page))
+		return NULL;
+
+	/*
+	 * We could have already allocated an eb for this page
+	 * and attached one so lets see if we can get a ref on
+	 * the existing eb, and if we can we know it's good and
+	 * we can just return that one, else we know we can just
+	 * overwrite page->private.
+	 */
+	exists = (struct extent_buffer *)page->private;
+	if (atomic_inc_not_zero(&exists->refs)) {
+		mark_extent_buffer_accessed(exists, page);
+		return exists;
+	}
+
+	WARN_ON(PageDirty(page));
+	/*
+	 * The page belongs to an eb which is being freed.
+	 * Detach it from previous eb so that we can reuse it.
+	 */
+	detach_page_private(page);
+	return NULL;
+}
+
 struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 					  u64 start, u64 owner_root, int level)
 {
@@ -5293,30 +5323,12 @@ struct extent_buffer *alloc_extent_buffer(struct btrfs_fs_info *fs_info,
 		}
 
 		spin_lock(&mapping->private_lock);
-		if (PagePrivate(p)) {
-			/*
-			 * We could have already allocated an eb for this page
-			 * and attached one so lets see if we can get a ref on
-			 * the existing eb, and if we can we know it's good and
-			 * we can just return that one, else we know we can just
-			 * overwrite page->private.
-			 */
-			exists = (struct extent_buffer *)p->private;
-			if (atomic_inc_not_zero(&exists->refs)) {
-				spin_unlock(&mapping->private_lock);
-				unlock_page(p);
-				put_page(p);
-				mark_extent_buffer_accessed(exists, p);
-				goto free_eb;
-			}
-			exists = NULL;
-			WARN_ON(PageDirty(p));
-
-			/*
-			 * Do this so attach doesn't complain and we need to
-			 * drop the ref the old guy had.
-			 */
-			detach_page_private(page);
+		exists = grab_extent_buffer_from_page(p);
+		if (exists) {
+			spin_unlock(&mapping->private_lock);
+			unlock_page(p);
+			put_page(p);
+			goto free_eb;
 		}
 		attach_extent_buffer_page(eb, p);
 		spin_unlock(&mapping->private_lock);
-- 
2.29.2