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