1 files changed, 66 insertions, 0 deletions
diff --git a/include/linux/cpumask_types.h b/include/linux/cpumask_types.h
new file mode 100644
index 000000000000..461ed1b6bcdb
--- /dev/null
+++ b/include/linux/cpumask_types.h
@@ -0,0 +1,66 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef __LINUX_CPUMASK_TYPES_H
+#define __LINUX_CPUMASK_TYPES_H
+
+#include <linux/bitops.h>
+#include <linux/threads.h>
+
+/* Don't assign or return these: may not be this big! */
+typedef struct cpumask { DECLARE_BITMAP(bits, NR_CPUS); } cpumask_t;
+
+/**
+ * cpumask_bits - get the bits in a cpumask
+ * @maskp: the struct cpumask *
+ *
+ * You should only assume nr_cpu_ids bits of this mask are valid.  This is
+ * a macro so it's const-correct.
+ */
+#define cpumask_bits(maskp) ((maskp)->bits)
+
+/*
+ * cpumask_var_t: struct cpumask for stack usage.
+ *
+ * Oh, the wicked games we play!  In order to make kernel coding a
+ * little more difficult, we typedef cpumask_var_t to an array or a
+ * pointer: doing &mask on an array is a noop, so it still works.
+ *
+ * i.e.
+ *	cpumask_var_t tmpmask;
+ *	if (!alloc_cpumask_var(&tmpmask, GFP_KERNEL))
+ *		return -ENOMEM;
+ *
+ *	  ... use 'tmpmask' like a normal struct cpumask * ...
+ *
+ *	free_cpumask_var(tmpmask);
+ *
+ *
+ * However, one notable exception is there. alloc_cpumask_var() allocates
+ * only nr_cpumask_bits bits (in the other hand, real cpumask_t always has
+ * NR_CPUS bits). Therefore you don't have to dereference cpumask_var_t.
+ *
+ *	cpumask_var_t tmpmask;
+ *	if (!alloc_cpumask_var(&tmpmask, GFP_KERNEL))
+ *		return -ENOMEM;
+ *
+ *	var = *tmpmask;
+ *
+ * This code makes NR_CPUS length memcopy and brings to a memory corruption.
+ * cpumask_copy() provide safe copy functionality.
+ *
+ * Note that there is another evil here: If you define a cpumask_var_t
+ * as a percpu variable then the way to obtain the address of the cpumask
+ * structure differently influences what this_cpu_* operation needs to be
+ * used. Please use this_cpu_cpumask_var_t in those cases. The direct use
+ * of this_cpu_ptr() or this_cpu_read() will lead to failures when the
+ * other type of cpumask_var_t implementation is configured.
+ *
+ * Please also note that __cpumask_var_read_mostly can be used to declare
+ * a cpumask_var_t variable itself (not its content) as read mostly.
+ */
+#ifdef CONFIG_CPUMASK_OFFSTACK
+typedef struct cpumask *cpumask_var_t;
+#else
+typedef struct cpumask cpumask_var_t[1];
+#endif /* CONFIG_CPUMASK_OFFSTACK */
+
+#endif /* __LINUX_CPUMASK_TYPES_H */