Clarify terminolgy around cpu ids and array length
[lttng-ust.git] / src / common / smp.h
1 /*
2 * SPDX-License-Identifier: LGPL-2.1-only
3 *
4 * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
5 */
6
7 #ifndef _UST_COMMON_SMP_H
8 #define _UST_COMMON_SMP_H
9
10 #define LTTNG_UST_CPUMASK_SIZE 4096
11
12 /*
13 * Get the CPU possible mask string from sysfs.
14 *
15 * buf: the buffer where the mask will be read.
16 * max_bytes: the maximum number of bytes to write in the buffer.
17 *
18 * Returns the number of bytes read or -1 on error.
19 */
20 int get_possible_cpu_mask_from_sysfs(char *buf, size_t max_bytes)
21 __attribute__((visibility("hidden")));
22
23 /*
24 * Get the number of possible CPUs in the system from either
25 * sysconf(_SC_NPROCESSORS_CONF) or some other mechanism depending on the libc.
26 *
27 * Returns the number of possible CPUs in the system or 0 on error.
28 */
29 int get_num_possible_cpus_fallback(void)
30 __attribute__((visibility("hidden")));
31
32 /*
33 * Get the highest CPU id from a CPU mask.
34 *
35 * pmask: the mask to parse.
36 * len: the len of the mask excluding '\0'.
37 *
38 * Returns the highest CPU id from the mask or -1 on error.
39 */
40 int get_max_cpuid_from_mask(const char *pmask, size_t len)
41 __attribute__((visibility("hidden")));
42
43 /*
44 * Returns the length of an array that could contain a per-CPU element for each
45 * possible CPU id for the lifetime of the process.
46 *
47 * We currently assume CPU ids are contiguous up the maximum CPU id.
48 *
49 * If the cache is not yet initialized, get the value from
50 * "/sys/devices/system/cpu/possible" or fallback to sysconf and cache it.
51 *
52 * If all methods fail, don't populate the cache and return 0.
53 */
54 int get_possible_cpus_array_len(void)
55 __attribute__((visibility("hidden")));
56
57 #define for_each_possible_cpu(cpu) \
58 for ((cpu) = 0; (cpu) < get_possible_cpus_array_len(); (cpu)++)
59
60 #endif /* _UST_COMMON_SMP_H */
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