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From: Hans Petter Selasky <hselasky@FreeBSD.org>
Date: Wed, 6 Jun 2018 13:59:51 +0000 (UTC)
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Subject: svn commit: r334712 - head/sys/compat/linuxkpi/common/include/asm
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Author: hselasky
Date: Wed Jun  6 13:59:51 2018
New Revision: 334712
URL: https://svnweb.freebsd.org/changeset/base/334712

Log:
  Implement the atomic_dec_if_positive() function in the LinuxKPI.
  
  Submitted by:	Johannes Lundberg <johalun0@gmail.com>
  MFC after:	1 week
  Sponsored by:	Mellanox Technologies
  Sponsored by:	Limelight Networks

Modified:
  head/sys/compat/linuxkpi/common/include/asm/atomic.h

Modified: head/sys/compat/linuxkpi/common/include/asm/atomic.h
==============================================================================
--- head/sys/compat/linuxkpi/common/include/asm/atomic.h	Wed Jun  6 13:37:31 2018	(r334711)
+++ head/sys/compat/linuxkpi/common/include/asm/atomic.h	Wed Jun  6 13:59:51 2018	(r334712)
@@ -235,6 +235,22 @@ atomic_cmpxchg(atomic_t *v, int old, int new)
 	__ret.val;							\
 })
 
+static inline int
+atomic_dec_if_positive(atomic_t *v)
+{
+	int retval;
+	int curr;
+
+	do {
+		curr = atomic_read(v);
+		retval = curr - 1;
+		if (unlikely(retval < 0))
+			break;
+	} while (!likely(atomic_cmpset_int(&v->counter, curr, retval)));
+
+	return (retval);
+}
+
 #define	LINUX_ATOMIC_OP(op, c_op)				\
 static inline void atomic_##op(int i, atomic_t *v)		\
 {								\