From: Jens Axboe <axboe@fb.com>
Date: Wed, 26 Apr 2017 20:20:21 +0000 (-0600)
Subject: seqlock: add simple user space code for sequence locks
X-Git-Tag: fio-2.20~34
X-Git-Url: https://git.kernel.dk/?p=fio.git;a=commitdiff_plain;h=c6bb62bc0140d7e5dd90481420cdc40dd9955225;hp=10c37df111032901e790cd57e7df43a42edd8ba8;ds=sidebyside

seqlock: add simple user space code for sequence locks

Signed-off-by: Jens Axboe <axboe@fb.com>
---

diff --git a/lib/seqlock.h b/lib/seqlock.h
new file mode 100644
index 00000000..1ac1eb6b
--- /dev/null
+++ b/lib/seqlock.h
@@ -0,0 +1,48 @@
+#ifndef FIO_SEQLOCK_H
+#define FIO_SEQLOCK_H
+
+#include "../arch/arch.h"
+
+struct seqlock {
+	volatile int sequence;
+};
+
+static inline void seqlock_init(struct seqlock *s)
+{
+	s->sequence = 0;
+}
+
+static inline unsigned int read_seqlock_begin(struct seqlock *s)
+{
+	unsigned int seq;
+
+	do {
+		seq = s->sequence;
+		if (!(seq & 1))
+			break;
+		nop;
+	} while (1);
+
+	read_barrier();
+	return seq;
+}
+
+static inline bool read_seqlock_retry(struct seqlock *s, unsigned int seq)
+{
+	read_barrier();
+	return s->sequence != seq;
+}
+
+static inline void write_seqlock_begin(struct seqlock *s)
+{
+	s->sequence++;
+	write_barrier();
+}
+
+static inline void write_seqlock_end(struct seqlock *s)
+{
+	write_barrier();
+	s->sequence++;
+}
+
+#endif