[PATCH V2 4/5] libxfs: add kernel-compatible completion API

[Chandan Babu R <chandan.babu@oracle.com>]

From: Dave Chinner <dchinner@redhat.com>

This is needed for the kernel buffer cache conversion to be able
to wait on IO synchrnously. It is implemented with pthread mutexes
and conditional variables.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
---
 include/Makefile     |  1 +
 include/completion.h | 61 ++++++++++++++++++++++++++++++++++++++++++++
 include/libxfs.h     |  1 +
 libxfs/libxfs_priv.h |  1 +
 4 files changed, 64 insertions(+)
 create mode 100644 include/completion.h

diff --git a/include/Makefile b/include/Makefile
index f7c40a5c..98031e70 100644
--- a/include/Makefile
+++ b/include/Makefile
@@ -12,6 +12,7 @@ LIBHFILES = libxfs.h \
 	atomic.h \
 	bitops.h \
 	cache.h \
+	completion.h \
 	hlist.h \
 	kmem.h \
 	list.h \
diff --git a/include/completion.h b/include/completion.h
new file mode 100644
index 00000000..92194c3f
--- /dev/null
+++ b/include/completion.h
@@ -0,0 +1,61 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2019 RedHat, Inc.
+ * All Rights Reserved.
+ */
+#ifndef __LIBXFS_COMPLETION_H__
+#define __LIBXFS_COMPLETION_H__
+
+/*
+ * This implements kernel compatible completion semantics. This is slightly
+ * different to the way pthread conditional variables work in that completions
+ * can be signalled before the waiter tries to wait on the variable. In the
+ * pthread case, the completion is ignored and the waiter goes to sleep, whilst
+ * the kernel will see that the completion has already been completed and so
+ * will not block. This is handled through the addition of the the @signalled
+ * flag in the struct completion.
+ */
+struct completion {
+	pthread_mutex_t		lock;
+	pthread_cond_t		cond;
+	bool			signalled; /* for kernel completion behaviour */
+	int			waiters;
+};
+
+static inline void
+init_completion(struct completion *w)
+{
+	pthread_mutex_init(&w->lock, NULL);
+	pthread_cond_init(&w->cond, NULL);
+	w->signalled = false;
+}
+
+static inline void
+complete(struct completion *w)
+{
+	pthread_mutex_lock(&w->lock);
+	w->signalled = true;
+	pthread_cond_broadcast(&w->cond);
+	pthread_mutex_unlock(&w->lock);
+}
+
+/*
+ * Support for mulitple waiters requires that we count the number of waiters
+ * we have and only clear the signalled variable once all those waiters have
+ * been woken.
+ */
+static inline void
+wait_for_completion(struct completion *w)
+{
+	pthread_mutex_lock(&w->lock);
+	if (!w->signalled) {
+		w->waiters++;
+		pthread_cond_wait(&w->cond, &w->lock);
+		w->waiters--;
+	}
+	if (!w->waiters)
+		w->signalled = false;
+	pthread_mutex_unlock(&w->lock);
+}
+
+#endif /* __LIBXFS_COMPLETION_H__ */
diff --git a/include/libxfs.h b/include/libxfs.h
index a494a1d4..61475347 100644
--- a/include/libxfs.h
+++ b/include/libxfs.h
@@ -19,6 +19,7 @@
 #include "libfrog/radix-tree.h"
 #include "atomic.h"
 #include "spinlock.h"
+#include "completion.h"
 
 #include "xfs_types.h"
 #include "xfs_fs.h"
diff --git a/libxfs/libxfs_priv.h b/libxfs/libxfs_priv.h
index e1e90268..9f28fd90 100644
--- a/libxfs/libxfs_priv.h
+++ b/libxfs/libxfs_priv.h
@@ -49,6 +49,7 @@
 #include "libfrog/radix-tree.h"
 #include "atomic.h"
 #include "spinlock.h"
+#include "completion.h"
 
 #include "xfs_types.h"
 #include "xfs_arch.h"
-- 
2.30.2