On Wed, Sep 25, 2013 at 2:20 PM, Liu Ping Fan <[email protected]> wrote: > From: Paolo Bonzini <[email protected]> > > Seqlock implementation for QEMU. Usage idiom > > reader: > do{ > start = seqlock_read_begin() > > }while(seqlock_read_try(start)) > > writer: > seqlock_write_lock() > ... > seqlock_write_unlock() > > initialization: > seqlock_init(QemuSeqLock *sl, QemuMutex *mutex) > where mutex could be NULL if the caller will provide extra lock > protection for seqlock_write_lock. > > Signed-off-by: Paolo Bonzini <[email protected]>
Signed-off-by: Liu Ping Fan <[email protected]> > --- > include/qemu/seqlock.h | 72 > ++++++++++++++++++++++++++++++++++++++++++++++++++ > 1 file changed, 72 insertions(+) > create mode 100644 include/qemu/seqlock.h > > diff --git a/include/qemu/seqlock.h b/include/qemu/seqlock.h > new file mode 100644 > index 0000000..3ff118a > --- /dev/null > +++ b/include/qemu/seqlock.h > @@ -0,0 +1,72 @@ > +/* > + * Seqlock implementation for QEMU > + * > + * Copyright Red Hat, Inc. 2013 > + * > + * Author: > + * Paolo Bonzini <[email protected]> > + * > + * This work is licensed under the terms of the GNU GPL, version 2 or later. > + * See the COPYING file in the top-level directory. > + * > + */ > +#ifndef QEMU_SEQLOCK_H > +#define QEMU_SEQLOCK_H 1 > + > +#include <qemu/atomic.h> > +#include <qemu/thread.h> > + > +typedef struct QemuSeqLock QemuSeqLock; > + > +struct QemuSeqLock { > + QemuMutex *mutex; > + unsigned sequence; > +}; > + > +static inline void seqlock_init(QemuSeqLock *sl, QemuMutex *mutex) > +{ > + sl->mutex = mutex; > + sl->sequence = 0; > +} > + > +/* Lock out other writers and update the count. */ > +static inline void seqlock_write_lock(QemuSeqLock *sl) > +{ > + if (sl->mutex) { > + qemu_mutex_lock(sl->mutex); > + } > + ++sl->sequence; > + > + /* Write sequence before updating other fields. */ > + smp_wmb(); > +} > + > +static inline void seqlock_write_unlock(QemuSeqLock *sl) > +{ > + /* Write other fields before finalizing sequence. */ > + smp_wmb(); > + > + ++sl->sequence; > + if (sl->mutex) { > + qemu_mutex_unlock(sl->mutex); > + } > +} > + > +static inline unsigned seqlock_read_begin(QemuSeqLock *sl) > +{ > + /* Always fail if a write is in progress. */ > + unsigned ret = sl->sequence & ~1; > + > + /* Read sequence before reading other fields. */ > + smp_rmb(); > + return ret; > +} > + > +static int seqlock_read_retry(const QemuSeqLock *sl, unsigned start) > +{ > + /* Read other fields before reading final sequence. */ > + smp_rmb(); > + return unlikely(sl->sequence != start); > +} > + > +#endif > -- > 1.8.1.4 >
