73804b66427f409626b532d1b1e12b01f5f124ff
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 <sys/types.h>
37 #include "usterr-signal-safe.h"
39 #define __max(a,b) ((a)>(b)?(a):(b))
41 int __num_possible_cpus
;
44 * As a fallback to parsing the CPU mask in "/sys/devices/system/cpu/possible",
45 * iterate on all the folders in "/sys/devices/system/cpu" that start with
46 * "cpu" followed by an integer, keep the highest CPU id encountered during
47 * this iteration and add 1 to get a number of CPUs.
49 * Then get the value from sysconf(_SC_NPROCESSORS_CONF) as a fallback and
50 * return the highest one.
52 * On Linux, using the value from sysconf can be unreliable since the way it
53 * counts CPUs varies between C libraries and even between versions of the same
54 * library. If we used it directly, getcpu() could return a value greater than
55 * this sysconf, in which case the arrays indexed by processor would overflow.
57 * As another example, the MUSL libc implementation of the _SC_NPROCESSORS_CONF
58 * sysconf does not return the number of configured CPUs in the system but
59 * relies on the cpu affinity mask of the current task.
61 * Returns 0 or less on error.
63 int get_num_possible_cpus_fallback(void)
70 cpudir
= opendir("/sys/devices/system/cpu");
75 * Iterate on all directories named "cpu" followed by an integer.
77 while ((entry
= readdir(cpudir
))) {
78 if (entry
->d_type
== DT_DIR
&&
79 strncmp(entry
->d_name
, "cpu", 3) == 0) {
84 cpu_id
= strtol(entry
->d_name
+ 3, &endptr
, 10);
85 if ((cpu_id
< LONG_MAX
) && (endptr
!= entry
->d_name
+ 3)
86 && (*endptr
== '\0')) {
87 if (cpu_id
> max_cpuid
)
97 * If the max CPU id is out of bound, set it to -1 so it results in a
100 if (max_cpuid
< 0 || max_cpuid
> INT_MAX
)
105 * Get the sysconf value as a last resort. Keep the highest number.
107 return __max(sysconf(_SC_NPROCESSORS_CONF
), max_cpuid
+ 1);
111 * Get the CPU possible mask string from sysfs.
113 * buf: the buffer where the mask will be read.
114 * max_bytes: the maximum number of bytes to write in the buffer.
116 * Returns the number of bytes read or -1 on error.
118 int get_possible_cpu_mask_from_sysfs(char *buf
, size_t max_bytes
)
120 ssize_t bytes_read
= 0;
121 size_t total_bytes_read
= 0;
122 int fd
= -1, ret
= -1;
127 fd
= open("/sys/devices/system/cpu/possible", O_RDONLY
);
132 bytes_read
= read(fd
, buf
+ total_bytes_read
,
133 max_bytes
- total_bytes_read
);
135 if (bytes_read
< 0) {
136 if (errno
== EINTR
) {
137 continue; /* retry operation */
143 total_bytes_read
+= bytes_read
;
144 assert(total_bytes_read
<= max_bytes
);
145 } while (max_bytes
> total_bytes_read
&& bytes_read
> 0);
148 * Make sure the mask read is a null terminated string.
150 if (total_bytes_read
< max_bytes
)
151 buf
[total_bytes_read
] = '\0';
153 buf
[max_bytes
- 1] = '\0';
155 if (total_bytes_read
> INT_MAX
)
158 ret
= (int) total_bytes_read
;
161 if (fd
>= 0 && close(fd
) < 0)
168 * Get the number of CPUs from the possible cpu mask.
170 * pmask: the mask to parse.
171 * len: the len of the mask excluding '\0'.
173 * Returns the number of possible CPUs from the mask or 0 on error.
175 int get_num_possible_cpus_from_mask(const char *pmask
, size_t len
)
178 unsigned long cpu_index
;
181 /* We need at least one char to read */
185 /* Start from the end to read the last CPU index. */
186 for (i
= len
- 1; i
> 0; i
--) {
187 /* Break when we hit the first separator. */
188 if ((pmask
[i
] == ',') || (pmask
[i
] == '-')) {
194 cpu_index
= strtoul(&pmask
[i
], &endptr
, 10);
196 if ((&pmask
[i
] != endptr
) && (cpu_index
< INT_MAX
))
197 return (int) cpu_index
+ 1;
203 void _get_num_possible_cpus(void)
206 char buf
[LTTNG_UST_CPUMASK_SIZE
];
208 /* Get the possible cpu mask from sysfs, fallback to sysconf. */
209 ret
= get_possible_cpu_mask_from_sysfs((char *) &buf
, LTTNG_UST_CPUMASK_SIZE
);
213 /* Parse the possible cpu mask, on failure fallback to sysconf. */
214 ret
= get_num_possible_cpus_from_mask((char *) &buf
, ret
);
219 /* Fallback to sysconf. */
220 ret
= get_num_possible_cpus_fallback();
223 /* If all methods failed, don't store the value. */
227 __num_possible_cpus
= ret
;
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