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/* 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/bvecq.h>
#include <linux/uio.h>
/*
* Rolling buffer. Whilst the buffer is live and in use, folios and bvecq
* 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 bvecq 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 bvecq *head; /* Producer's insertion point */
struct bvecq *tail; /* Consumer's removal point */
struct iov_iter iter; /* Iterator tracking what's left in the buffer */
u8 first_tail_slot; /* First slot in ->tail */
bool for_writeback; /* T if being used for writeback */
};
int rolling_buffer_init(struct rolling_buffer *roll, unsigned int direction,
gfp_t gfp, bool for_writeback);
int rolling_buffer_make_space(struct rolling_buffer *roll, gfp_t gfp);
ssize_t rolling_buffer_bulk_load_from_ra(struct rolling_buffer *roll,
struct readahead_control *ractl,
gfp_t gfp);
ssize_t rolling_buffer_append(struct rolling_buffer *roll, struct folio *folio, gfp_t gfp);
struct bvecq *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 */
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