From: Dave Chinner <dchinner@xxxxxxxxxx>
Implemented vi pthread mutexes.
On Linux, fast pthread mutexes don't actaully check which thread
owns the lock on unlock, so can be used in situations where the
unlock occurs in a different thread to the lock. This is
non-portable behaviour, so if other platforms are supported, this
may need to be converted to posix semaphores.
Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx>
---
include/Makefile | 1 +
include/libxfs.h | 1 +
include/sema.h | 35 +++++++++++++++++++++++++++++++++++
libxfs/libxfs_priv.h | 1 +
4 files changed, 38 insertions(+)
create mode 100644 include/sema.h
diff --git a/include/Makefile b/include/Makefile
index 98031e70fa0d..ce89d0237c19 100644
--- a/include/Makefile
+++ b/include/Makefile
@@ -17,6 +17,7 @@ LIBHFILES = libxfs.h \
kmem.h \
list.h \
parent.h \
+ sema.h \
spinlock.h \
xfs_inode.h \
xfs_log_recover.h \
diff --git a/include/libxfs.h b/include/libxfs.h
index d03ec8aeaf5c..923a376bd71a 100644
--- a/include/libxfs.h
+++ b/include/libxfs.h
@@ -20,6 +20,7 @@
#include "atomic.h"
#include "spinlock.h"
#include "completion.h"
+#include "sema.h"
#include "xfs_types.h"
#include "xfs_fs.h"
diff --git a/include/sema.h b/include/sema.h
new file mode 100644
index 000000000000..bcccb156b0ea
--- /dev/null
+++ b/include/sema.h
@@ -0,0 +1,35 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2019-20 RedHat, Inc.
+ * All Rights Reserved.
+ */
+#ifndef __LIBXFS_SEMA_H__
+#define __LIBXFS_SEMA_H__
+
+/*
+ * This implements kernel compatible semaphore _exclusion_ semantics. It does
+ * not implement counting semaphore behaviour.
+ *
+ * This makes use of the fact that fast pthread mutexes on Linux don't check
+ * that the unlocker is the same thread that locked the mutex, and hence can be
+ * unlocked in a different thread safely.
+ *
+ * If this needs to be portable or we require counting semaphore behaviour in
+ * libxfs code, this requires re-implementation based on posix semaphores.
+ */
+struct semaphore {
+ pthread_mutex_t lock;
+};
+
+#define sema_init(l, nolock) \
+do { \
+ pthread_mutex_init(&(l)->lock, NULL); \
+ if (!nolock) \
+ pthread_mutex_lock(&(l)->lock); \
+} while (0)
+
+#define down(l) pthread_mutex_lock(&(l)->lock)
+#define down_trylock(l) pthread_mutex_trylock(&(l)->lock)
+#define up(l) pthread_mutex_unlock(&(l)->lock)
+
+#endif /* __LIBXFS_SEMA_H__ */
diff --git a/libxfs/libxfs_priv.h b/libxfs/libxfs_priv.h
index 5cbc4fe69732..7be3f7615fdd 100644
--- a/libxfs/libxfs_priv.h
+++ b/libxfs/libxfs_priv.h
@@ -50,6 +50,7 @@
#include "atomic.h"
#include "spinlock.h"
#include "completion.h"
+#include "sema.h"
#include "xfs_types.h"
#include "xfs_arch.h"
--
2.28.0
