Fedora kernel-2.6.17-1.2142_FC4 patched with stable patch-2.6.17.4-vs2.0.2-rc26.diff

[linux-2.6.git] / Documentation / atomic_ops.txt

diff --git a/Documentation/atomic_ops.txt b/Documentation/atomic_ops.txt
index 8eedaa2..23a1c24 100644 (file)
--- a/Documentation/atomic_ops.txt
+++ b/Documentation/atomic_ops.txt
@@ -115,6 +115,33 @@ boolean is return which indicates whether the resulting counter value
 is negative.  It requires explicit memory barrier semantics around the
 operation.
 
 is negative.  It requires explicit memory barrier semantics around the
 operation.
 

+Then:
+
+       int atomic_cmpxchg(atomic_t *v, int old, int new);
+
+This performs an atomic compare exchange operation on the atomic value v,
+with the given old and new values. Like all atomic_xxx operations,
+atomic_cmpxchg will only satisfy its atomicity semantics as long as all
+other accesses of *v are performed through atomic_xxx operations.
+
+atomic_cmpxchg requires explicit memory barriers around the operation.
+
+The semantics for atomic_cmpxchg are the same as those defined for 'cas'
+below.
+
+Finally:
+
+       int atomic_add_unless(atomic_t *v, int a, int u);
+
+If the atomic value v is not equal to u, this function adds a to v, and
+returns non zero. If v is equal to u then it returns zero. This is done as
+an atomic operation.
+
+atomic_add_unless requires explicit memory barriers around the operation.
+
+atomic_inc_not_zero, equivalent to atomic_add_unless(v, 1, 0)
+
+

 If a caller requires memory barrier semantics around an atomic_t
 operation which does not return a value, a set of interfaces are
 defined which accomplish this:
 If a caller requires memory barrier semantics around an atomic_t
 operation which does not return a value, a set of interfaces are
 defined which accomplish this: