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1/* SPDX-License-Identifier: GPL-2.0 */
2#ifndef __LINUX_CPUMASK_TYPES_H
3#define __LINUX_CPUMASK_TYPES_H
4
5#include <linux/bitops.h>
6#include <linux/threads.h>
7
8/* Don't assign or return these: may not be this big! */
9typedef struct cpumask { DECLARE_BITMAP(bits, NR_CPUS); } cpumask_t;
10
11/**
12 * cpumask_bits - get the bits in a cpumask
13 * @maskp: the struct cpumask *
14 *
15 * You should only assume nr_cpu_ids bits of this mask are valid. This is
16 * a macro so it's const-correct.
17 */
18#define cpumask_bits(maskp) ((maskp)->bits)
19
20/*
21 * cpumask_var_t: struct cpumask for stack usage.
22 *
23 * Oh, the wicked games we play! In order to make kernel coding a
24 * little more difficult, we typedef cpumask_var_t to an array or a
25 * pointer: doing &mask on an array is a noop, so it still works.
26 *
27 * i.e.
28 * cpumask_var_t tmpmask;
29 * if (!alloc_cpumask_var(&tmpmask, GFP_KERNEL))
30 * return -ENOMEM;
31 *
32 * ... use 'tmpmask' like a normal struct cpumask * ...
33 *
34 * free_cpumask_var(tmpmask);
35 *
36 *
37 * However, one notable exception is there. alloc_cpumask_var() allocates
38 * only nr_cpumask_bits bits (in the other hand, real cpumask_t always has
39 * NR_CPUS bits). Therefore you don't have to dereference cpumask_var_t.
40 *
41 * cpumask_var_t tmpmask;
42 * if (!alloc_cpumask_var(&tmpmask, GFP_KERNEL))
43 * return -ENOMEM;
44 *
45 * var = *tmpmask;
46 *
47 * This code makes NR_CPUS length memcopy and brings to a memory corruption.
48 * cpumask_copy() provide safe copy functionality.
49 *
50 * Note that there is another evil here: If you define a cpumask_var_t
51 * as a percpu variable then the way to obtain the address of the cpumask
52 * structure differently influences what this_cpu_* operation needs to be
53 * used. Please use this_cpu_cpumask_var_t in those cases. The direct use
54 * of this_cpu_ptr() or this_cpu_read() will lead to failures when the
55 * other type of cpumask_var_t implementation is configured.
56 *
57 * Please also note that __cpumask_var_read_mostly can be used to declare
58 * a cpumask_var_t variable itself (not its content) as read mostly.
59 */
60#ifdef CONFIG_CPUMASK_OFFSTACK
61typedef struct cpumask *cpumask_var_t;
62#else
63typedef struct cpumask cpumask_var_t[1];
64#endif /* CONFIG_CPUMASK_OFFSTACK */
65
66#endif /* __LINUX_CPUMASK_TYPES_H */