[07/11] hlist-bl: add hlist_bl_fake()

Commit Message

Dave Chinner Dec. 6, 2023, 6:05 a.m. UTC

From: Dave Chinner <[e-mail]>

in preparation for switching the VFS inode cache over the hlist_bl
lists, we nee dto be able to fake a list node that looks like it is
hased for correct operation of filesystems that don't directly use
the VFS indoe cache.

Signed-off-by: Dave Chinner <[e-mail]>
---
 include/linux/list_bl.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

Comments

Al Viro Dec. 7, 2023, 3:05 a.m. UTC | #1

On Wed, Dec 06, 2023 at 05:05:36PM +1100, Dave Chinner wrote:
> From: Dave Chinner <[e-mail]>
> 
> in preparation for switching the VFS inode cache over the hlist_bl
> lists, we nee dto be able to fake a list node that looks like it is
> hased for correct operation of filesystems that don't directly use
> the VFS indoe cache.

I'd probably put it as "we need hlist_bl counterparts of hlist_fake()
and hlist_add_fake()"...

Patch

diff --git a/include/linux/list_bl.h b/include/linux/list_bl.h
index ae1b541446c9..8ee2bf5af131 100644
--- a/include/linux/list_bl.h
+++ b/include/linux/list_bl.h
@@ -143,6 +143,28 @@  static inline void hlist_bl_del_init(struct hlist_bl_node *n)
 	}
 }
 
+/**
+ * hlist_bl_add_fake - create a fake list consisting of a single headless node
+ * @n: Node to make a fake list out of
+ *
+ * This makes @n appear to be its own predecessor on a headless hlist.
+ * The point of this is to allow things like hlist_bl_del() to work correctly
+ * in cases where there is no list.
+ */
+static inline void hlist_bl_add_fake(struct hlist_bl_node *n)
+{
+	n->pprev = &n->next;
+}
+
+/**
+ * hlist_fake: Is this node a fake hlist_bl?
+ * @h: Node to check for being a self-referential fake hlist.
+ */
+static inline bool hlist_bl_fake(struct hlist_bl_node *n)
+{
+	return n->pprev == &n->next;
+}
+
 static inline void hlist_bl_lock(struct hlist_bl_head *b)
 {
 	bit_spin_lock(0, (unsigned long *)b);