4 * Copyright (C) 2011-2012 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
5 * Copyright (C) 2019 Michael Jeanson <mjeanson@efficios.com>
7 * This library is free software; you can redistribute it and/or
8 * modify it under the terms of the GNU Lesser General Public
9 * License as published by the Free Software Foundation; only
10 * version 2.1 of the License.
12 * This library is distributed in the hope that it will be useful,
13 * but WITHOUT ANY WARRANTY; without even the implied warranty of
14 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 * Lesser General Public License for more details.
17 * You should have received a copy of the GNU Lesser General Public
18 * License along with this library; if not, write to the Free Software
19 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
34 #include "usterr-signal-safe.h"
36 int __num_possible_cpus
;
38 #if (defined(__GLIBC__) || defined( __UCLIBC__))
39 int get_num_possible_cpus_fallback(void)
41 /* On Linux, when some processors are offline
42 * _SC_NPROCESSORS_CONF counts the offline
43 * processors, whereas _SC_NPROCESSORS_ONLN
44 * does not. If we used _SC_NPROCESSORS_ONLN,
45 * getcpu() could return a value greater than
46 * this sysconf, in which case the arrays
47 * indexed by processor would overflow.
49 return sysconf(_SC_NPROCESSORS_CONF
);
55 * The MUSL libc implementation of the _SC_NPROCESSORS_CONF sysconf does not
56 * return the number of configured CPUs in the system but relies on the cpu
57 * affinity mask of the current task.
59 * So instead we use a strategy similar to GLIBC's, counting the cpu
60 * directories in "/sys/devices/system/cpu" and fallback on the value from
61 * sysconf if it fails.
68 #include <sys/types.h>
70 #define __max(a,b) ((a)>(b)?(a):(b))
72 int get_num_possible_cpus_fallback(void)
78 cpudir
= opendir("/sys/devices/system/cpu");
83 * Count the number of directories named "cpu" followed by and
84 * integer. This is the same strategy as glibc uses.
86 while ((entry
= readdir(cpudir
))) {
87 if (entry
->d_type
== DT_DIR
&&
88 strncmp(entry
->d_name
, "cpu", 3) == 0) {
91 unsigned long cpu_num
;
93 cpu_num
= strtoul(entry
->d_name
+ 3, &endptr
, 10);
94 if ((cpu_num
< ULONG_MAX
) && (endptr
!= entry
->d_name
+ 3)
95 && (*endptr
== '\0')) {
103 * Get the sysconf value as a fallback. Keep the highest number.
105 return __max(sysconf(_SC_NPROCESSORS_CONF
), count
);
110 * Get the CPU possible mask string from sysfs.
112 * buf: the buffer where the mask will be read.
113 * max_bytes: the maximum number of bytes to write in the buffer.
115 * Returns the number of bytes read or -1 on error.
117 int get_possible_cpu_mask_from_sysfs(char *buf
, size_t max_bytes
)
119 ssize_t bytes_read
= 0;
120 size_t total_bytes_read
= 0;
121 int fd
= -1, ret
= -1;
126 fd
= open("/sys/devices/system/cpu/possible", O_RDONLY
);
131 bytes_read
= read(fd
, buf
+ total_bytes_read
,
132 max_bytes
- total_bytes_read
);
134 if (bytes_read
< 0) {
135 if (errno
== EINTR
) {
136 continue; /* retry operation */
142 total_bytes_read
+= bytes_read
;
143 assert(total_bytes_read
<= max_bytes
);
144 } while (max_bytes
> total_bytes_read
&& bytes_read
> 0);
147 * Make sure the mask read is a null terminated string.
149 if (total_bytes_read
< max_bytes
)
150 buf
[total_bytes_read
] = '\0';
152 buf
[max_bytes
- 1] = '\0';
154 if (total_bytes_read
> INT_MAX
)
157 ret
= (int) total_bytes_read
;
160 if (fd
>= 0 && close(fd
) < 0)
167 * Get the number of CPUs from the possible cpu mask.
169 * pmask: the mask to parse.
170 * len: the len of the mask excluding '\0'.
172 * Returns the number of possible CPUs from the mask or 0 on error.
174 int get_num_possible_cpus_from_mask(const char *pmask
, size_t len
)
177 unsigned long cpu_index
;
180 /* We need at least one char to read */
184 /* Start from the end to read the last CPU index. */
185 for (i
= len
- 1; i
> 0; i
--) {
186 /* Break when we hit the first separator. */
187 if ((pmask
[i
] == ',') || (pmask
[i
] == '-')) {
193 cpu_index
= strtoul(&pmask
[i
], &endptr
, 10);
196 * If we read a CPU index, increment it by one to return a number of
199 if ((&pmask
[i
] != endptr
) && (cpu_index
< INT_MAX
))
200 return (int) cpu_index
+ 1;
206 void _get_num_possible_cpus(void)
209 char buf
[LTTNG_UST_CPUMASK_SIZE
];
211 /* Get the possible cpu mask from sysfs, fallback to sysconf. */
212 ret
= get_possible_cpu_mask_from_sysfs((char *) &buf
, LTTNG_UST_CPUMASK_SIZE
);
216 /* Parse the possible cpu mask, on failure fallback to sysconf. */
217 ret
= get_num_possible_cpus_from_mask((char *) &buf
, ret
);
222 /* Fallback to sysconf. */
223 ret
= get_num_possible_cpus_fallback();
226 /* If all methods failed, don't store the value. */
230 __num_possible_cpus
= ret
;
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