1 /*-
2  * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
3  *
4  * Copyright (c) 2021 Vladimir Kondratyev <wulf@FreeBSD.org>
5  *
6  * Redistribution and use in source and binary forms, with or without
7  * modification, are permitted provided that the following conditions are
8  * met:
9  * 1. Redistributions of source code must retain the above copyright
10  *    notice, this list of conditions and the following disclaimer.
11  * 2. Redistributions in binary form must reproduce the above copyright
12  *    notice, this list of conditions and the following disclaimer in
13  *    the documentation and/or other materials provided with the
14  *    distribution.
15  *
16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
17  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
18  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
19  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
20  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
21  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
22  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
23  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
24  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
25  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
26  * SUCH DAMAGE.
27  */
28 
29 #ifndef _LINUXKPI_LINUX_SEQLOCK_H__
30 #define	_LINUXKPI_LINUX_SEQLOCK_H__
31 
32 #include <sys/param.h>
33 #include <sys/lock.h>
34 #include <sys/mutex.h>
35 #include <sys/seqc.h>
36 
37 struct lock_class_key;
38 
39 struct seqcount {
40 	seqc_t		seqc;
41 };
42 typedef struct seqcount seqcount_t;
43 
44 struct seqlock {
45 	struct mtx	seql_lock;
46 	struct seqcount	seql_count;
47 };
48 typedef struct seqlock seqlock_t;
49 
50 static inline void
51 __seqcount_init(struct seqcount *seqcount, const char *name __unused,
52     struct lock_class_key *key __unused)
53 {
54 	seqcount->seqc = 0;
55 }
56 #define	seqcount_init(seqcount)	__seqcount_init(seqcount, NULL, NULL)
57 
58 static inline void
59 write_seqcount_begin(struct seqcount *seqcount)
60 {
61 	seqc_sleepable_write_begin(&seqcount->seqc);
62 }
63 
64 static inline void
65 write_seqcount_end(struct seqcount *seqcount)
66 {
67 	seqc_sleepable_write_end(&seqcount->seqc);
68 }
69 
70 /*
71  * XXX: Are predicts from inline functions still not honored by clang?
72  */
73 #define	__read_seqcount_retry(seqcount, gen)	\
74 	(!seqc_consistent_no_fence(&(seqcount)->seqc, gen))
75 #define	read_seqcount_retry(seqcount, gen)	\
76 	(!seqc_consistent(&(seqcount)->seqc, gen))
77 
78 static inline unsigned
79 read_seqcount_begin(const struct seqcount *seqcount)
80 {
81 	return (seqc_read(&seqcount->seqc));
82 }
83 
84 static inline unsigned
85 raw_read_seqcount(const struct seqcount *seqcount)
86 {
87 	return (seqc_read_any(&seqcount->seqc));
88 }
89 
90 static inline void
91 seqlock_init(struct seqlock *seqlock)
92 {
93 	/*
94 	 * Don't enroll to witness(4) to avoid orphaned references after struct
95 	 * seqlock has been freed. There is no seqlock destructor exists so we
96 	 * can't expect automatic mtx_destroy() execution before free().
97 	 */
98 	mtx_init(&seqlock->seql_lock, "seqlock", NULL, MTX_DEF|MTX_NOWITNESS);
99 	seqcount_init(&seqlock->seql_count);
100 }
101 
102 static inline void
103 write_seqlock(struct seqlock *seqlock)
104 {
105 	mtx_lock(&seqlock->seql_lock);
106 	write_seqcount_begin(&seqlock->seql_count);
107 }
108 
109 static inline void
110 write_sequnlock(struct seqlock *seqlock)
111 {
112 	write_seqcount_end(&seqlock->seql_count);
113 	mtx_unlock(&seqlock->seql_lock);
114 }
115 
116 #define	write_seqlock_irqsave(seqlock, flags)	do {	\
117 	(flags) = 0;					\
118 	write_seqlock(seqlock);				\
119 } while (0)
120 
121 static inline void
122 write_sequnlock_irqrestore(struct seqlock *seqlock,
123     unsigned long flags __unused)
124 {
125 	write_sequnlock(seqlock);
126 }
127 
128 static inline unsigned
129 read_seqbegin(const struct seqlock *seqlock)
130 {
131 	return (read_seqcount_begin(&seqlock->seql_count));
132 }
133 
134 #define	read_seqretry(seqlock, gen)	\
135 	read_seqcount_retry(&(seqlock)->seql_count, gen)
136 
137 #endif	/* _LINUXKPI_LINUX_SEQLOCK_H__ */
138