66 lines
1.4 KiB
C
66 lines
1.4 KiB
C
/*
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* Seqlock implementation for QEMU
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*
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* Copyright Red Hat, Inc. 2013
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*
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* Author:
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* Paolo Bonzini <pbonzini@redhat.com>
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*
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* This work is licensed under the terms of the GNU GPL, version 2 or later.
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* See the COPYING file in the top-level directory.
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*
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*/
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#ifndef QEMU_SEQLOCK_H
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#define QEMU_SEQLOCK_H
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#include "qemu/atomic.h"
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#include "qemu/thread.h"
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typedef struct QemuSeqLock QemuSeqLock;
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struct QemuSeqLock {
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unsigned sequence;
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};
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static inline void seqlock_init(QemuSeqLock *sl)
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{
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sl->sequence = 0;
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}
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/* Lock out other writers and update the count. */
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static inline void seqlock_write_begin(QemuSeqLock *sl)
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{
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atomic_set(&sl->sequence, sl->sequence + 1);
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/* Write sequence before updating other fields. */
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smp_wmb();
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}
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static inline void seqlock_write_end(QemuSeqLock *sl)
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{
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/* Write other fields before finalizing sequence. */
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smp_wmb();
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atomic_set(&sl->sequence, sl->sequence + 1);
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}
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static inline unsigned seqlock_read_begin(QemuSeqLock *sl)
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{
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/* Always fail if a write is in progress. */
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unsigned ret = atomic_read(&sl->sequence);
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/* Read sequence before reading other fields. */
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smp_rmb();
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return ret & ~1;
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}
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static inline int seqlock_read_retry(const QemuSeqLock *sl, unsigned start)
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{
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/* Read other fields before reading final sequence. */
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smp_rmb();
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return unlikely(atomic_read(&sl->sequence) != start);
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}
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#endif
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