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