| 1 | /* SPDX-License-Identifier: GPL-2.0 */ |
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| 2 | /* |
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| 3 | * See Documentation/core-api/circular-buffers.rst for more information. |
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| 4 | */ |
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| 5 | |
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| 6 | #ifndef _LINUX_CIRC_BUF_H |
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| 7 | #define _LINUX_CIRC_BUF_H 1 |
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| 8 | |
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| 9 | struct circ_buf { |
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| 10 | char *buf; |
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| 11 | int head; |
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| 12 | int tail; |
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| 13 | }; |
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| 14 | |
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| 15 | /* Return count in buffer. */ |
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| 16 | #define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1)) |
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| 17 | |
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| 18 | /* Return space available, 0..size-1. We always leave one free char |
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| 19 | as a completely full buffer has head == tail, which is the same as |
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| 20 | empty. */ |
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| 21 | #define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size)) |
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| 22 | |
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| 23 | /* Return count up to the end of the buffer. Carefully avoid |
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| 24 | accessing head and tail more than once, so they can change |
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| 25 | underneath us without returning inconsistent results. */ |
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| 26 | #define CIRC_CNT_TO_END(head,tail,size) \ |
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| 27 | ({int end = (size) - (tail); \ |
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| 28 | int n = ((head) + end) & ((size)-1); \ |
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| 29 | n < end ? n : end;}) |
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| 30 | |
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| 31 | /* Return space available up to the end of the buffer. */ |
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| 32 | #define CIRC_SPACE_TO_END(head,tail,size) \ |
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| 33 | ({int end = (size) - 1 - (head); \ |
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| 34 | int n = (end + (tail)) & ((size)-1); \ |
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| 35 | n <= end ? n : end+1;}) |
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| 36 | |
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| 37 | #endif /* _LINUX_CIRC_BUF_H */ |
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| 38 | |
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