tools/power/cpupower/utils/helpers/sysfs.c

Source file repositories/reference/linux-study-clean/tools/power/cpupower/utils/helpers/sysfs.c

File Facts

System
Linux kernel
Corpus path
tools/power/cpupower/utils/helpers/sysfs.c
Extension
.c
Size
10591 bytes
Lines
472
Domain
Support Tooling And Documentation
Bucket
tools
Inferred role
Support Tooling And Documentation: implementation source
Status
source implementation candidate

Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

Dependency Surface

Detected Declarations

Annotated Snippet

// SPDX-License-Identifier: GPL-2.0-only
/*
 *  (C) 2004-2009  Dominik Brodowski <linux@dominikbrodowski.de>
 *  (C) 2011       Thomas Renninger <trenn@novell.com> Novell Inc.
 */

#include <stdio.h>
#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>

#include "helpers/sysfs.h"

unsigned int sysfs_read_file(const char *path, char *buf, size_t buflen)
{
	int fd;
	ssize_t numread;

	fd = open(path, O_RDONLY);
	if (fd == -1)
		return 0;

	numread = read(fd, buf, buflen - 1);
	if (numread < 1) {
		close(fd);
		return 0;
	}

	buf[numread] = '\0';
	close(fd);

	return (unsigned int) numread;
}

/*
 * Detect whether a CPU is online
 *
 * Returns:
 *     1 -> if CPU is online
 *     0 -> if CPU is offline
 *     negative errno values in error case
 */
int sysfs_is_cpu_online(unsigned int cpu)
{
	char path[SYSFS_PATH_MAX];
	int fd;
	ssize_t numread;
	unsigned long long value;
	char linebuf[MAX_LINE_LEN];
	char *endp;
	struct stat statbuf;

	snprintf(path, sizeof(path), PATH_TO_CPU "cpu%u", cpu);

	if (stat(path, &statbuf) != 0)
		return 0;

	/*
	 * kernel without CONFIG_HOTPLUG_CPU
	 * -> cpuX directory exists, but not cpuX/online file
	 */
	snprintf(path, sizeof(path), PATH_TO_CPU "cpu%u/online", cpu);
	if (stat(path, &statbuf) != 0)
		return 1;

	fd = open(path, O_RDONLY);
	if (fd == -1)
		return -errno;

	numread = read(fd, linebuf, MAX_LINE_LEN - 1);
	if (numread < 1) {
		close(fd);
		return -EIO;
	}
	linebuf[numread] = '\0';
	close(fd);

	value = strtoull(linebuf, &endp, 0);
	if (value > 1)
		return -EINVAL;

	return value;
}

/* CPUidle idlestate specific /sys/devices/system/cpu/cpuX/cpuidle/ access */

Annotation

Implementation Notes