Linux kernel & device driver programming

Cross-Referenced Linux and Device Driver Code

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Version: [ 2.6.11.8 ] [ 2.6.25 ] [ 2.6.25.8 ] [ 2.6.31.13 ] Architecture: [ i386 ]
  1 #ifndef _LINUX_CIRC_BUF_H
  2 #define _LINUX_CIRC_BUF_H 1
  3 
  4 struct circ_buf {
  5         char *buf;
  6         int head;
  7         int tail;
  8 };
  9 
 10 /* Return count in buffer.  */
 11 #define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1))
 12 
 13 /* Return space available, 0..size-1.  We always leave one free char
 14    as a completely full buffer has head == tail, which is the same as
 15    empty.  */
 16 #define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size))
 17 
 18 /* Return count up to the end of the buffer.  Carefully avoid
 19    accessing head and tail more than once, so they can change
 20    underneath us without returning inconsistent results.  */
 21 #define CIRC_CNT_TO_END(head,tail,size) \
 22         ({int end = (size) - (tail); \
 23           int n = ((head) + end) & ((size)-1); \
 24           n < end ? n : end;})
 25 
 26 /* Return space available up to the end of the buffer.  */
 27 #define CIRC_SPACE_TO_END(head,tail,size) \
 28         ({int end = (size) - 1 - (head); \
 29           int n = (end + (tail)) & ((size)-1); \
 30           n <= end ? n : end+1;})
 31 
 32 #endif /* _LINUX_CIRC_BUF_H  */
 33 
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