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A rolling buffer is a series of folios held in a list of folio_queues. New folios and folio_queue structs may be inserted at the head simultaneously with spent ones being removed from the tail without the need for locking. The rolling buffer includes an iov_iter and it has to be careful managing this as the list of folio_queues is extended such that an oops doesn't incurred because the iterator was pointing to the end of a folio_queue segment that got appended to and then removed. We need to use the mechanism twice, once for read and once for write, and, in future patches, we will use a second rolling buffer to handle bounce buffering for content encryption. Signed-off-by: David Howells <dhowells@redhat.com> Link: https://lore.kernel.org/r/20241216204124.3752367-6-dhowells@redhat.com cc: Jeff Layton <jlayton@kernel.org> cc: netfs@lists.linux.dev cc: linux-fsdevel@vger.kernel.org Signed-off-by: Christian Brauner <brauner@kernel.org>
62 lines
2.2 KiB
C
62 lines
2.2 KiB
C
/* SPDX-License-Identifier: GPL-2.0-or-later */
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/* Rolling buffer of folios
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*
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* Copyright (C) 2024 Red Hat, Inc. All Rights Reserved.
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* Written by David Howells (dhowells@redhat.com)
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*/
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#ifndef _ROLLING_BUFFER_H
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#define _ROLLING_BUFFER_H
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#include <linux/folio_queue.h>
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#include <linux/uio.h>
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/*
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* Rolling buffer. Whilst the buffer is live and in use, folios and folio
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* queue segments can be added to one end by one thread and removed from the
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* other end by another thread. The buffer isn't allowed to be empty; it must
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* always have at least one folio_queue in it so that neither side has to
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* modify both queue pointers.
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*
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* The iterator in the buffer is extended as buffers are inserted. It can be
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* snapshotted to use a segment of the buffer.
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*/
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struct rolling_buffer {
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struct folio_queue *head; /* Producer's insertion point */
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struct folio_queue *tail; /* Consumer's removal point */
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struct iov_iter iter; /* Iterator tracking what's left in the buffer */
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u8 next_head_slot; /* Next slot in ->head */
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u8 first_tail_slot; /* First slot in ->tail */
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};
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/*
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* Snapshot of a rolling buffer.
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*/
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struct rolling_buffer_snapshot {
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struct folio_queue *curr_folioq; /* Queue segment in which current folio resides */
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unsigned char curr_slot; /* Folio currently being read */
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unsigned char curr_order; /* Order of folio */
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};
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/* Marks to store per-folio in the internal folio_queue structs. */
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#define ROLLBUF_MARK_1 BIT(0)
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#define ROLLBUF_MARK_2 BIT(1)
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int rolling_buffer_init(struct rolling_buffer *roll, unsigned int rreq_id,
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unsigned int direction);
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int rolling_buffer_make_space(struct rolling_buffer *roll);
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ssize_t rolling_buffer_load_from_ra(struct rolling_buffer *roll,
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struct readahead_control *ractl,
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struct folio_batch *put_batch);
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ssize_t rolling_buffer_append(struct rolling_buffer *roll, struct folio *folio,
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unsigned int flags);
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struct folio_queue *rolling_buffer_delete_spent(struct rolling_buffer *roll);
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void rolling_buffer_clear(struct rolling_buffer *roll);
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static inline void rolling_buffer_advance(struct rolling_buffer *roll, size_t amount)
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{
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iov_iter_advance(&roll->iter, amount);
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}
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#endif /* _ROLLING_BUFFER_H */
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