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From:   Dave Chinner <david@fromorbit.com>
To:     linux-fsdevel@vger.kernel.org
Cc:     linux-kernel@vger.kernel.org
Subject: [PATCH 2/3] hlist-bl: add hlist_bl_fake()
Date:   Tue,  6 Apr 2021 22:33:42 +1000
Message-Id: <20210406123343.1739669-3-david@fromorbit.com>
In-Reply-To: <20210406123343.1739669-1-david@fromorbit.com>
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From: Dave Chinner <dchinner@redhat.com>

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 <dchinner@redhat.com>
---
 include/linux/list_bl.h | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)

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);
-- 
2.31.0