Add atomic_dec_not_last_64

Signed-off-by: Mateusz Guzik <mjguzik@gmail.com>

include/os/freebsd/spl/sys/atomic.h

@@ -149,6 +149,23 @@ atomic_cas_64(volatile uint64_t *target, uint64_t cmp, uint64_t newval)
 #endif
 #endif
 
+static inline int
+atomic_dec_not_last_64(volatile uint64_t *target)
+{
+	uint64_t val, oldval;
+
+	val = *target;
+	for (;;) {
+		if (val <= 1) {
+			return (0);
+		}
+		oldval = atomic_cas_64(target, val, val - 1);
+		if (oldval == val)
+			return (1);
+		val = oldval;
+	}
+}
+
 static __inline void
 atomic_inc_64(volatile uint64_t *target)
 {

include/os/linux/spl/sys/atomic.h

@@ -62,6 +62,7 @@
 #define	atomic_swap_64(v, x)	atomic64_xchg((atomic64_t *)(v), x)
 #define	atomic_load_64(v)	atomic64_read((atomic64_t *)(v))
 #define	atomic_store_64(v, x)	atomic64_set((atomic64_t *)(v), x)
+#define	atomic_dec_not_last_64(v) atomic64_dec_if_positive((atomic64_t *)(v))
 
 #ifdef _LP64
 static __inline__ void *

lib/libspl/atomic.c

@@ -62,6 +62,24 @@ ATOMIC_DEC(uchar, uchar_t)
 ATOMIC_DEC(ushort, ushort_t)
 ATOMIC_DEC(uint, uint_t)
 ATOMIC_DEC(ulong, ulong_t)
+
+int
+atomic_dec_not_last_64(volatile uint64_t *target)
+{
+	uint64_t val, oldval;
+
+	val = *target;
+	for (;;) {
+		if (val <= 1) {
+			return (0);
+		}
+		oldval = atomic_cas_64(target, val, val - 1);
+		if (oldval == val)
+			return (1);
+		val = oldval;
+	}
+}
+
 /* END CSTYLED */
 
 

lib/libspl/include/atomic.h

@@ -155,6 +155,7 @@ extern uint_t atomic_dec_uint_nv(volatile uint_t *);
 extern ulong_t atomic_dec_ulong_nv(volatile ulong_t *);
 #if defined(_INT64_TYPE)
 extern uint64_t atomic_dec_64_nv(volatile uint64_t *);
+extern int atomic_dec_not_last_64(volatile uint64_t *);
 #endif
 
 /*