1 files changed, 61 insertions, 0 deletions
diff --git a/include/linux/rolling_buffer.h b/include/linux/rolling_buffer.h
new file mode 100644
index 000000000000..ac15b1ffdd83
--- /dev/null
+++ b/include/linux/rolling_buffer.h
@@ -0,0 +1,61 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/* Rolling buffer of folios
+ *
+ * Copyright (C) 2024 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#ifndef _ROLLING_BUFFER_H
+#define _ROLLING_BUFFER_H
+
+#include <linux/folio_queue.h>
+#include <linux/uio.h>
+
+/*
+ * Rolling buffer.  Whilst the buffer is live and in use, folios and folio
+ * queue segments can be added to one end by one thread and removed from the
+ * other end by another thread.  The buffer isn't allowed to be empty; it must
+ * always have at least one folio_queue in it so that neither side has to
+ * modify both queue pointers.
+ *
+ * The iterator in the buffer is extended as buffers are inserted.  It can be
+ * snapshotted to use a segment of the buffer.
+ */
+struct rolling_buffer {
+	struct folio_queue	*head;		/* Producer's insertion point */
+	struct folio_queue	*tail;		/* Consumer's removal point */
+	struct iov_iter		iter;		/* Iterator tracking what's left in the buffer */
+	u8			next_head_slot;	/* Next slot in ->head */
+	u8			first_tail_slot; /* First slot in ->tail */
+};
+
+/*
+ * Snapshot of a rolling buffer.
+ */
+struct rolling_buffer_snapshot {
+	struct folio_queue	*curr_folioq;	/* Queue segment in which current folio resides */
+	unsigned char		curr_slot;	/* Folio currently being read */
+	unsigned char		curr_order;	/* Order of folio */
+};
+
+/* Marks to store per-folio in the internal folio_queue structs. */
+#define ROLLBUF_MARK_1	BIT(0)
+#define ROLLBUF_MARK_2	BIT(1)
+
+int rolling_buffer_init(struct rolling_buffer *roll, unsigned int rreq_id,
+			unsigned int direction);
+int rolling_buffer_make_space(struct rolling_buffer *roll);
+ssize_t rolling_buffer_load_from_ra(struct rolling_buffer *roll,
+				    struct readahead_control *ractl,
+				    struct folio_batch *put_batch);
+ssize_t rolling_buffer_append(struct rolling_buffer *roll, struct folio *folio,
+			      unsigned int flags);
+struct folio_queue *rolling_buffer_delete_spent(struct rolling_buffer *roll);
+void rolling_buffer_clear(struct rolling_buffer *roll);
+
+static inline void rolling_buffer_advance(struct rolling_buffer *roll, size_t amount)
+{
+	iov_iter_advance(&roll->iter, amount);
+}
+
+#endif /* _ROLLING_BUFFER_H */