/* * See Documentation/circular-buffers.txt 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  */