1 | /* |
2 | * Seqlock implementation for QEMU |
3 | * |
4 | * Copyright Red Hat, Inc. 2013 |
5 | * |
6 | * Author: |
7 | * Paolo Bonzini <pbonzini@redhat.com> |
8 | * |
9 | * This work is licensed under the terms of the GNU GPL, version 2 or later. |
10 | * See the COPYING file in the top-level directory. |
11 | * |
12 | */ |
13 | |
14 | #ifndef QEMU_SEQLOCK_H |
15 | #define QEMU_SEQLOCK_H |
16 | |
17 | #include "qemu/atomic.h" |
18 | #include "qemu/thread.h" |
19 | #include "qemu/lockable.h" |
20 | |
21 | typedef struct QemuSeqLock QemuSeqLock; |
22 | |
23 | struct QemuSeqLock { |
24 | unsigned sequence; |
25 | }; |
26 | |
27 | static inline void seqlock_init(QemuSeqLock *sl) |
28 | { |
29 | sl->sequence = 0; |
30 | } |
31 | |
32 | /* Lock out other writers and update the count. */ |
33 | static inline void seqlock_write_begin(QemuSeqLock *sl) |
34 | { |
35 | atomic_set(&sl->sequence, sl->sequence + 1); |
36 | |
37 | /* Write sequence before updating other fields. */ |
38 | smp_wmb(); |
39 | } |
40 | |
41 | static inline void seqlock_write_end(QemuSeqLock *sl) |
42 | { |
43 | /* Write other fields before finalizing sequence. */ |
44 | smp_wmb(); |
45 | |
46 | atomic_set(&sl->sequence, sl->sequence + 1); |
47 | } |
48 | |
49 | /* Lock out other writers and update the count. */ |
50 | static inline void seqlock_write_lock_impl(QemuSeqLock *sl, QemuLockable *lock) |
51 | { |
52 | qemu_lockable_lock(lock); |
53 | seqlock_write_begin(sl); |
54 | } |
55 | #define seqlock_write_lock(sl, lock) \ |
56 | seqlock_write_lock_impl(sl, QEMU_MAKE_LOCKABLE(lock)) |
57 | |
58 | /* Lock out other writers and update the count. */ |
59 | static inline void seqlock_write_unlock_impl(QemuSeqLock *sl, QemuLockable *lock) |
60 | { |
61 | qemu_lockable_unlock(lock); |
62 | seqlock_write_begin(sl); |
63 | } |
64 | #define seqlock_write_unlock(sl, lock) \ |
65 | seqlock_write_unlock_impl(sl, QEMU_MAKE_LOCKABLE(lock)) |
66 | |
67 | |
68 | static inline unsigned seqlock_read_begin(const QemuSeqLock *sl) |
69 | { |
70 | /* Always fail if a write is in progress. */ |
71 | unsigned ret = atomic_read(&sl->sequence); |
72 | |
73 | /* Read sequence before reading other fields. */ |
74 | smp_rmb(); |
75 | return ret & ~1; |
76 | } |
77 | |
78 | static inline int seqlock_read_retry(const QemuSeqLock *sl, unsigned start) |
79 | { |
80 | /* Read other fields before reading final sequence. */ |
81 | smp_rmb(); |
82 | return unlikely(atomic_read(&sl->sequence) != start); |
83 | } |
84 | |
85 | #endif |
86 | |