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! */
9 typedef 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
61 typedef struct cpumask *cpumask_var_t;
62 #else
63 typedef struct cpumask cpumask_var_t[1];
64 #endif /* CONFIG_CPUMASK_OFFSTACK */
65 
66 #endif /* __LINUX_CPUMASK_TYPES_H */
67