/* SPDX-License-Identifier: GPL-2.0 */ /* * See Documentation/core-api/circular-buffers.rst for more information. */ #ifndef _LINUX_CIRC_BUF_H #define _LINUX_CIRC_BUF_H 1 struct circ_buf { char *buf; int head; int tail; }; /* Return count in buffer. */ #define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1)) /* Return space available, 0..size-1. We always leave one free char as a completely full buffer has head == tail, which is the same as empty. */ #define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size)) /* Return count up to the end of the buffer. Carefully avoid accessing head and tail more than once, so they can change underneath us without returning inconsistent results. */ #define CIRC_CNT_TO_END(head,tail,size) \ ({int end = (size) - (tail); \ int n = ((head) + end) & ((size)-1); \ n < end ? n : end;}) /* Return space available up to the end of the buffer. */ #define CIRC_SPACE_TO_END(head,tail,size) \ ({int end = (size) - 1 - (head); \ int n = (end + (tail)) & ((size)-1); \ n <= end ? n : end+1;}) #endif /* _LINUX_CIRC_BUF_H */