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      1 #ifndef FIO_SEQLOCK_H
      2 #define FIO_SEQLOCK_H
      3 
      4 #include "../arch/arch.h"
      5 
      6 struct seqlock {
      7 	volatile int sequence;
      8 };
      9 
     10 static inline void seqlock_init(struct seqlock *s)
     11 {
     12 	s->sequence = 0;
     13 }
     14 
     15 static inline unsigned int read_seqlock_begin(struct seqlock *s)
     16 {
     17 	unsigned int seq;
     18 
     19 	do {
     20 		seq = s->sequence;
     21 		if (!(seq & 1))
     22 			break;
     23 		nop;
     24 	} while (1);
     25 
     26 	read_barrier();
     27 	return seq;
     28 }
     29 
     30 static inline bool read_seqlock_retry(struct seqlock *s, unsigned int seq)
     31 {
     32 	read_barrier();
     33 	return s->sequence != seq;
     34 }
     35 
     36 static inline void write_seqlock_begin(struct seqlock *s)
     37 {
     38 	s->sequence++;
     39 	write_barrier();
     40 }
     41 
     42 static inline void write_seqlock_end(struct seqlock *s)
     43 {
     44 	write_barrier();
     45 	s->sequence++;
     46 }
     47 
     48 #endif
     49