X-Git-Url: http://git.lttng.org/?p=userspace-rcu.git;a=blobdiff_plain;f=src%2Fcompat-smp.h;fp=src%2Fcompat-smp.h;h=7240d2f66b3c8af059338df28bc032192abdcd20;hp=0000000000000000000000000000000000000000;hb=5cfe81b7ddff9543d451746de9965cac58c67182;hpb=ff59d427166510229fd3925748ed91c90741ae9c diff --git a/src/compat-smp.h b/src/compat-smp.h new file mode 100644 index 0000000..7240d2f --- /dev/null +++ b/src/compat-smp.h @@ -0,0 +1,275 @@ +/* + * SPDX-License-Identifier: LGPL-2.1-only + * + * Copyright (C) 2011-2012 Mathieu Desnoyers + * Copyright (C) 2019 Michael Jeanson + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include + +#define URCU_CPUMASK_SIZE 4096 + +#if defined(HAVE_SYSCONF) +static inline int get_num_possible_cpus_sysconf(void) +{ + return sysconf(_SC_NPROCESSORS_CONF); +} +#else +/* + * On platforms without sysconf(), always return -1. + */ +static inline int get_num_possible_cpus_sysconf(void) +{ + return -1; +} +#endif + +/* + * Get the highest CPU id from sysfs. + * + * Iterate on all the folders in "/sys/devices/system/cpu" that start with + * "cpu" followed by an integer, keep the highest CPU id encountered during + * this iteration and add 1 to get a number of CPUs. + * + * Returns the highest CPU id, or -1 on error. + */ +static inline int _get_max_cpuid_from_sysfs(const char *path) +{ + long max_cpuid = -1; + + DIR *cpudir; + struct dirent *entry; + + assert(path); + + cpudir = opendir(path); + if (cpudir == NULL) + goto end; + + /* + * Iterate on all directories named "cpu" followed by an integer. + */ + while ((entry = readdir(cpudir))) { + if (entry->d_type == DT_DIR && + strncmp(entry->d_name, "cpu", 3) == 0) { + + char *endptr; + long cpu_id; + + cpu_id = strtol(entry->d_name + 3, &endptr, 10); + if ((cpu_id < LONG_MAX) && (endptr != entry->d_name + 3) + && (*endptr == '\0')) { + if (cpu_id > max_cpuid) + max_cpuid = cpu_id; + } + } + } + + if (closedir(cpudir)) + perror("closedir"); + + /* + * If the max CPU id is out of bound, set it to -1 so it results in a + * CPU num of 0. + */ + if (max_cpuid < 0 || max_cpuid > INT_MAX) + max_cpuid = -1; + +end: + return max_cpuid; +} + +static inline int get_max_cpuid_from_sysfs(void) +{ + return _get_max_cpuid_from_sysfs("/sys/devices/system/cpu"); +} + + +/* + * As a fallback to parsing the CPU mask in "/sys/devices/system/cpu/possible", + * iterate on all the folders in "/sys/devices/system/cpu" that start with + * "cpu" followed by an integer, keep the highest CPU id encountered during + * this iteration and add 1 to get a number of CPUs. + * + * Then get the value from sysconf(_SC_NPROCESSORS_CONF) as a fallback and + * return the highest one. + * + * On Linux, using the value from sysconf can be unreliable since the way it + * counts CPUs varies between C libraries and even between versions of the same + * library. If we used it directly, getcpu() could return a value greater than + * this sysconf, in which case the arrays indexed by processor would overflow. + * + * As another example, the MUSL libc implementation of the _SC_NPROCESSORS_CONF + * sysconf does not return the number of configured CPUs in the system but + * relies on the cpu affinity mask of the current task. + * + * Returns 0 or less on error. + */ +static inline int get_num_possible_cpus_fallback(void) +{ + /* + * Get the sysconf value as a last resort. Keep the highest number. + */ + return caa_max(get_num_possible_cpus_sysconf(), get_max_cpuid_from_sysfs() + 1); +} + +/* + * Get a CPU mask string from sysfs. + * + * buf: the buffer where the mask will be read. + * max_bytes: the maximum number of bytes to write in the buffer. + * path: file path to read the mask from. + * + * Returns the number of bytes read or -1 on error. + */ +static inline int get_cpu_mask_from_sysfs(char *buf, size_t max_bytes, const char *path) +{ + ssize_t bytes_read = 0; + size_t total_bytes_read = 0; + int fd = -1, ret = -1; + + assert(path); + + if (buf == NULL) + goto end; + + fd = open(path, O_RDONLY); + if (fd < 0) + goto end; + + do { + bytes_read = read(fd, buf + total_bytes_read, + max_bytes - total_bytes_read); + + if (bytes_read < 0) { + if (errno == EINTR) { + continue; /* retry operation */ + } else { + goto end; + } + } + + total_bytes_read += bytes_read; + assert(total_bytes_read <= max_bytes); + } while (max_bytes > total_bytes_read && bytes_read > 0); + + /* + * Make sure the mask read is a null terminated string. + */ + if (total_bytes_read < max_bytes) + buf[total_bytes_read] = '\0'; + else + buf[max_bytes - 1] = '\0'; + + if (total_bytes_read > INT_MAX) + goto end; + + ret = (int) total_bytes_read; + +end: + if (fd >= 0 && close(fd) < 0) + perror("close"); + + return ret; +} + +/* + * Get the CPU possible mask string from sysfs. + * + * buf: the buffer where the mask will be read. + * max_bytes: the maximum number of bytes to write in the buffer. + * + * Returns the number of bytes read or -1 on error. + */ +static inline int get_possible_cpu_mask_from_sysfs(char *buf, size_t max_bytes) +{ + return get_cpu_mask_from_sysfs(buf, max_bytes, + "/sys/devices/system/cpu/possible"); +} + +/* + * Get the highest CPU id from the possible CPU mask. + * + * pmask: the mask to parse. + * len: the len of the mask excluding '\0'. + * + * Returns the highest CPU id from the mask or -1 on error. + */ +static inline int get_max_cpuid_from_mask(const char *pmask, size_t len) +{ + ssize_t i; + unsigned long cpu_index; + char *endptr; + + /* We need at least one char to read */ + if (len < 1) + goto error; + + /* Start from the end to read the last CPU index. */ + for (i = len - 1; i > 0; i--) { + /* Break when we hit the first separator. */ + if ((pmask[i] == ',') || (pmask[i] == '-')) { + i++; + break; + } + } + + cpu_index = strtoul(&pmask[i], &endptr, 10); + + if ((&pmask[i] != endptr) && (cpu_index < INT_MAX)) + return (int) cpu_index; + +error: + return -1; +} + +#ifdef __linux__ +/* + * On Linux try sysfs first and fallback to sysconf. + */ +static inline int get_possible_cpus_array_len(void) +{ + int ret; + char buf[URCU_CPUMASK_SIZE]; + + /* Get the possible cpu mask from sysfs, fallback to sysconf. */ + ret = get_possible_cpu_mask_from_sysfs((char *) &buf, URCU_CPUMASK_SIZE); + if (ret <= 0) + goto fallback; + + /* Parse the possible cpu mask, on failure fallback to sysconf. */ + ret = get_max_cpuid_from_mask((char *) &buf, ret); + if (ret >= 0) { + /* Add 1 to convert from max cpuid to an array len. */ + ret++; + goto end; + } + +fallback: + /* Fallback to sysconf. */ + ret = get_num_possible_cpus_fallback(); + +end: + return ret; +} +#else +/* + * On other platforms, only use sysconf. + */ +static inline int get_possible_cpus_array_len(void) +{ + return get_num_possible_cpus_sysconf(); +} +#endif