2 * Copyright (c) 2017 François Tigeot <ftigeot@wolfpond.org>
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
8 * 1. Redistributions of source code must retain the above copyright
9 * notice unmodified, this list of conditions, and the following
11 * 2. Redistributions in binary form must reproduce the above copyright
12 * notice, this list of conditions and the following disclaimer in the
13 * documentation and/or other materials provided with the distribution.
15 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
16 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
17 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
18 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
19 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
20 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
21 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
22 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
23 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
24 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
27 #ifndef _LINUX_SEQLOCK_H_
28 #define _LINUX_SEQLOCK_H_
30 #include <linux/spinlock.h>
31 #include <linux/lockdep.h>
32 #include <linux/compiler.h>
41 seqlock_init(seqlock_t *sl)
44 spin_init(&sl->lock, "lsql");
48 * Writers always use a spinlock. We still use store barriers
49 * in order to quickly update the state of the sequence variable
53 write_seqlock(seqlock_t *sl)
61 write_sequnlock(seqlock_t *sl)
64 spin_unlock(&sl->lock);
69 * Read functions are fully unlocked.
70 * We use load barriers to obtain a reasonably up-to-date state
71 * for the sequence number.
73 static inline unsigned
74 read_seqbegin(const seqlock_t *sl)
76 return READ_ONCE(sl->sequence);
79 static inline unsigned
80 read_seqretry(const seqlock_t *sl, unsigned start)
83 return (sl->sequence != start);
86 #endif /* _LINUX_SEQLOCK_H_ */