forked from mirrors/linux
90fddabf58
Document the circular buffering capabilities available in Linux. Signed-off-by: David Howells <dhowells@redhat.com> Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> Reviewed-by: Randy Dunlap <rdunlap@xenotime.net> Reviewed-by: Stefan Richter <stefanr@s5r6.in-berlin.de> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
36 lines
1 KiB
C
36 lines
1 KiB
C
/*
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* See Documentation/circular-buffers.txt for more information.
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*/
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#ifndef _LINUX_CIRC_BUF_H
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#define _LINUX_CIRC_BUF_H 1
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struct circ_buf {
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char *buf;
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int head;
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int tail;
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};
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/* Return count in buffer. */
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#define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1))
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/* Return space available, 0..size-1. We always leave one free char
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as a completely full buffer has head == tail, which is the same as
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empty. */
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#define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size))
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/* Return count up to the end of the buffer. Carefully avoid
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accessing head and tail more than once, so they can change
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underneath us without returning inconsistent results. */
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#define CIRC_CNT_TO_END(head,tail,size) \
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({int end = (size) - (tail); \
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int n = ((head) + end) & ((size)-1); \
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n < end ? n : end;})
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/* Return space available up to the end of the buffer. */
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#define CIRC_SPACE_TO_END(head,tail,size) \
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({int end = (size) - 1 - (head); \
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int n = (end + (tail)) & ((size)-1); \
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n <= end ? n : end+1;})
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#endif /* _LINUX_CIRC_BUF_H */
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