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