include/linux/circ_buf.h

0001 /* SPDX-License-Identifier: GPL-2.0 */
0002 /*
0003  * See Documentation/core-api/circular-buffers.rst for more information.
0004  */
0005
0006 #ifndef _LINUX_CIRC_BUF_H
0007 #define _LINUX_CIRC_BUF_H 1
0008
0009 struct circ_buf {
0010     char *buf;
0011     int head;
0012     int tail;
0013 };
0014
0015 /* Return count in buffer.  */
0016 #define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1))
0017
0018 /* Return space available, 0..size-1.  We always leave one free char
0019    as a completely full buffer has head == tail, which is the same as
0020    empty.  */
0021 #define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size))
0022
0023 /* Return count up to the end of the buffer.  Carefully avoid
0024    accessing head and tail more than once, so they can change
0025    underneath us without returning inconsistent results.  */
0026 #define CIRC_CNT_TO_END(head,tail,size) \
0027     ({int end = (size) - (tail); \
0028       int n = ((head) + end) & ((size)-1); \
0029       n < end ? n : end;})
0030
0031 /* Return space available up to the end of the buffer.  */
0032 #define CIRC_SPACE_TO_END(head,tail,size) \
0033     ({int end = (size) - 1 - (head); \
0034       int n = (end + (tail)) & ((size)-1); \
0035       n <= end ? n : end+1;})
0036
0037 #endif /* _LINUX_CIRC_BUF_H  */