rolling_buffer.h

 1/* SPDX-License-Identifier: GPL-2.0-or-later */
 2/* Rolling buffer of folios
 3 *
 4 * Copyright (C) 2024 Red Hat, Inc. All Rights Reserved.
 5 * Written by David Howells (dhowells@redhat.com)
 6 */
 7
 8#ifndef _ROLLING_BUFFER_H
 9#define _ROLLING_BUFFER_H
10
11#include <linux/folio_queue.h>
12#include <linux/uio.h>
13
14/*
15 * Rolling buffer.  Whilst the buffer is live and in use, folios and folio
16 * queue segments can be added to one end by one thread and removed from the
17 * other end by another thread.  The buffer isn't allowed to be empty; it must
18 * always have at least one folio_queue in it so that neither side has to
19 * modify both queue pointers.
20 *
21 * The iterator in the buffer is extended as buffers are inserted.  It can be
22 * snapshotted to use a segment of the buffer.
23 */
24struct rolling_buffer {
25	struct folio_queue	*head;		/* Producer's insertion point */
26	struct folio_queue	*tail;		/* Consumer's removal point */
27	struct iov_iter		iter;		/* Iterator tracking what's left in the buffer */
28	u8			next_head_slot;	/* Next slot in ->head */
29	u8			first_tail_slot; /* First slot in ->tail */
30};
31
32/*
33 * Snapshot of a rolling buffer.
34 */
35struct rolling_buffer_snapshot {
36	struct folio_queue	*curr_folioq;	/* Queue segment in which current folio resides */
37	unsigned char		curr_slot;	/* Folio currently being read */
38	unsigned char		curr_order;	/* Order of folio */
39};
40
41/* Marks to store per-folio in the internal folio_queue structs. */
42#define ROLLBUF_MARK_1	BIT(0)
43#define ROLLBUF_MARK_2	BIT(1)
44
45int rolling_buffer_init(struct rolling_buffer *roll, unsigned int rreq_id,
46			unsigned int direction);
47int rolling_buffer_make_space(struct rolling_buffer *roll);
48ssize_t rolling_buffer_load_from_ra(struct rolling_buffer *roll,
49				    struct readahead_control *ractl,
50				    struct folio_batch *put_batch);
51ssize_t rolling_buffer_append(struct rolling_buffer *roll, struct folio *folio,
52			      unsigned int flags);
53struct folio_queue *rolling_buffer_delete_spent(struct rolling_buffer *roll);
54void rolling_buffer_clear(struct rolling_buffer *roll);
55
56static inline void rolling_buffer_advance(struct rolling_buffer *roll, size_t amount)
57{
58	iov_iter_advance(&roll->iter, amount);
59}
60
61#endif /* _ROLLING_BUFFER_H */