| 1 | /* SPDX-License-Identifier: GPL-2.0-or-later */ |
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| 2 | /* Rolling buffer of folios |
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| 3 | * |
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| 4 | * Copyright (C) 2024 Red Hat, Inc. All Rights Reserved. |
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| 5 | * Written by David Howells (dhowells@redhat.com) |
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| 6 | */ |
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| 7 | |
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| 8 | #ifndef _ROLLING_BUFFER_H |
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| 9 | #define _ROLLING_BUFFER_H |
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| 10 | |
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| 11 | #include <linux/folio_queue.h> |
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| 12 | #include <linux/uio.h> |
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| 13 | |
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| 14 | /* |
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| 15 | * Rolling buffer. Whilst the buffer is live and in use, folios and folio |
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| 16 | * queue segments can be added to one end by one thread and removed from the |
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| 17 | * other end by another thread. The buffer isn't allowed to be empty; it must |
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| 18 | * always have at least one folio_queue in it so that neither side has to |
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| 19 | * modify both queue pointers. |
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| 20 | * |
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| 21 | * The iterator in the buffer is extended as buffers are inserted. It can be |
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| 22 | * snapshotted to use a segment of the buffer. |
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| 23 | */ |
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| 24 | struct rolling_buffer { |
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| 25 | struct folio_queue *head; /* Producer's insertion point */ |
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| 26 | struct folio_queue *tail; /* Consumer's removal point */ |
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| 27 | struct iov_iter iter; /* Iterator tracking what's left in the buffer */ |
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| 28 | u8 next_head_slot; /* Next slot in ->head */ |
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| 29 | u8 first_tail_slot; /* First slot in ->tail */ |
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| 30 | }; |
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| 31 | |
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| 32 | /* |
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| 33 | * Snapshot of a rolling buffer. |
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| 34 | */ |
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| 35 | struct rolling_buffer_snapshot { |
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| 36 | struct folio_queue *curr_folioq; /* Queue segment in which current folio resides */ |
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| 37 | unsigned char curr_slot; /* Folio currently being read */ |
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| 38 | unsigned char curr_order; /* Order of folio */ |
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| 39 | }; |
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| 40 | |
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| 41 | /* Marks to store per-folio in the internal folio_queue structs. */ |
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| 42 | #define ROLLBUF_MARK_1 BIT(0) |
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| 43 | #define ROLLBUF_MARK_2 BIT(1) |
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| 44 | |
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| 45 | int rolling_buffer_init(struct rolling_buffer *roll, unsigned int rreq_id, |
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| 46 | unsigned int direction); |
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| 47 | int rolling_buffer_make_space(struct rolling_buffer *roll); |
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| 48 | ssize_t rolling_buffer_load_from_ra(struct rolling_buffer *roll, |
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| 49 | struct readahead_control *ractl, |
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| 50 | struct folio_batch *put_batch); |
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| 51 | ssize_t rolling_buffer_append(struct rolling_buffer *roll, struct folio *folio, |
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| 52 | unsigned int flags); |
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| 53 | struct folio_queue *rolling_buffer_delete_spent(struct rolling_buffer *roll); |
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| 54 | void rolling_buffer_clear(struct rolling_buffer *roll); |
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| 55 | |
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| 56 | static inline void rolling_buffer_advance(struct rolling_buffer *roll, size_t amount) |
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| 57 | { |
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| 58 | iov_iter_advance(i: &roll->iter, bytes: amount); |
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| 59 | } |
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| 60 | |
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| 61 | #endif /* _ROLLING_BUFFER_H */ |
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| 62 | |
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