include/linux/cpumask_types.h

   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 */