[PATCH 2/5] cpumask: Introduce for_each_cpu_andnot()

[Valentin Schneider]

for_each_cpu_and() is very convenient as it saves having to allocate a
temporary cpumask to store the result of cpumask_and(). The same issue
applies to cpumask_andnot() which doesn't actually need temporary storage
for iteration purposes.

Following what has been done for for_each_cpu_and(), introduce
for_each_cpu_andnot().

Signed-off-by: Valentin Schneider <vschneid@xxxxxxxxxx>
---
 include/linux/cpumask.h | 32 ++++++++++++++++++++++++++++++++
 lib/cpumask.c           | 19 +++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/include/linux/cpumask.h b/include/linux/cpumask.h
index fe29ac7cc469..a8b2ca160e57 100644
--- a/include/linux/cpumask.h
+++ b/include/linux/cpumask.h
@@ -157,6 +157,13 @@ static inline unsigned int cpumask_next_and(int n,
 	return n+1;
 }
 
+static inline unsigned int cpumask_next_andnot(int n,
+					    const struct cpumask *srcp,
+					    const struct cpumask *andp)
+{
+	return n+1;
+}
+
 static inline unsigned int cpumask_next_wrap(int n, const struct cpumask *mask,
 					     int start, bool wrap)
 {
@@ -194,6 +201,8 @@ static inline int cpumask_any_distribute(const struct cpumask *srcp)
 	for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask, (void)(start))
 #define for_each_cpu_and(cpu, mask1, mask2)	\
 	for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask1, (void)mask2)
+#define for_each_cpu_andnot(cpu, mask1, mask2)	\
+	for ((cpu) = 0; (cpu) < 1; (cpu)++, (void)mask1, (void)mask2)
 #else
 /**
  * cpumask_first - get the first cpu in a cpumask
@@ -259,6 +268,9 @@ static inline unsigned int cpumask_next_zero(int n, const struct cpumask *srcp)
 }
 
 int __pure cpumask_next_and(int n, const struct cpumask *, const struct cpumask *);
+int __pure cpumask_next_andnot(int n,
+			       const struct cpumask *src1p,
+			       const struct cpumask *src2p);
 int __pure cpumask_any_but(const struct cpumask *mask, unsigned int cpu);
 unsigned int cpumask_local_spread(unsigned int i, int node);
 int cpumask_any_and_distribute(const struct cpumask *src1p,
@@ -324,6 +336,26 @@ extern int cpumask_next_wrap(int n, const struct cpumask *mask, int start, bool
 	for ((cpu) = -1;						\
 		(cpu) = cpumask_next_and((cpu), (mask1), (mask2)),	\
 		(cpu) < nr_cpu_ids;)
+
+/**
+ * for_each_cpu_andnot - iterate over every cpu in one mask but not in another
+ * @cpu: the (optionally unsigned) integer iterator
+ * @mask1: the first cpumask pointer
+ * @mask2: the second cpumask pointer
+ *
+ * This saves a temporary CPU mask in many places.  It is equivalent to:
+ *	struct cpumask tmp;
+ *	cpumask_andnot(&tmp, &mask1, &mask2);
+ *	for_each_cpu(cpu, &tmp)
+ *		...
+ *
+ * After the loop, cpu is >= nr_cpu_ids.
+ */
+#define for_each_cpu_andnot(cpu, mask1, mask2)				\
+	for ((cpu) = -1;						\
+		(cpu) = cpumask_next_andnot((cpu), (mask1), (mask2)),	\
+		(cpu) < nr_cpu_ids;)
+
 #endif /* SMP */
 
 #define CPU_BITS_NONE						\
diff --git a/lib/cpumask.c b/lib/cpumask.c
index a971a82d2f43..6896ff4a08fd 100644
--- a/lib/cpumask.c
+++ b/lib/cpumask.c
@@ -42,6 +42,25 @@ int cpumask_next_and(int n, const struct cpumask *src1p,
 }
 EXPORT_SYMBOL(cpumask_next_and);
 
+/**
+ * cpumask_next_andnot - get the next cpu in *src1p & ~*src2p
+ * @n: the cpu prior to the place to search (ie. return will be > @n)
+ * @src1p: the first cpumask pointer
+ * @src2p: the second cpumask pointer
+ *
+ * Returns >= nr_cpu_ids if no further cpus set in *src1p & ~*src2p.
+ */
+int cpumask_next_andnot(int n, const struct cpumask *src1p,
+		     const struct cpumask *src2p)
+{
+	/* -1 is a legal arg here. */
+	if (n != -1)
+		cpumask_check(n);
+	return find_next_andnot_bit(cpumask_bits(src1p), cpumask_bits(src2p),
+		nr_cpumask_bits, n + 1);
+}
+EXPORT_SYMBOL(cpumask_next_andnot);
+
 /**
  * cpumask_any_but - return a "random" in a cpumask, but not this one.
  * @mask: the cpumask to search
-- 
2.31.1