tools/iio/iio_utils.c

// SPDX-License-Identifier: GPL-2.0-only
/* IIO - useful set of util functionality
 *
 * Copyright (c) 2008 Jonathan Cameron
 */
#include <string.h>
#include <stdlib.h>
#include <stdio.h>
#include <stdint.h>
#include <dirent.h>
#include <errno.h>
#include <ctype.h>
#include "iio_utils.h"

const char *iio_dir = "/sys/bus/iio/devices/";

static char * const iio_direction[] = {
	"in",
	"out",
};

/**
 * iioutils_break_up_name() - extract generic name from full channel name
 * @full_name: the full channel name
 * @generic_name: the output generic channel name
 *
 * Returns 0 on success, or a negative error code if string extraction failed.
 **/
int iioutils_break_up_name(const char *full_name, char **generic_name)
{
	char *current;
	char *w, *r;
	char *working, *prefix = "";
	int i, ret;

	for (i = 0; i < ARRAY_SIZE(iio_direction); i++)
		if (!strncmp(full_name, iio_direction[i],
			     strlen(iio_direction[i]))) {
			prefix = iio_direction[i];
			break;
		}

	current = strdup(full_name + strlen(prefix) + 1);
	if (!current)
		return -ENOMEM;

	working = strtok(current, "_\0");
	if (!working) {
		free(current);
		return -EINVAL;
	}

	w = working;
	r = working;

	while (*r != '\0') {
		if (!isdigit(*r)) {
			*w = *r;
			w++;
		}

		r++;
	}
	*w = '\0';
	ret = asprintf(generic_name, "%s_%s", prefix, working);
	free(current);

	return (ret == -1) ? -ENOMEM : 0;
}

/**
 * iioutils_get_type() - find and process _type attribute data
 * @is_signed: output whether channel is signed
 * @bytes: output how many bytes the channel storage occupies
 * @bits_used: output number of valid bits of data
 * @shift: output amount of bits to shift right data before applying bit mask
 * @mask: output a bit mask for the raw data
 * @be: output if data in big endian
 * @device_dir: the IIO device directory
 * @buffer_idx: the IIO buffer index
 * @name: the channel name
 * @generic_name: the channel type name
 *
 * Returns a value >= 0 on success, otherwise a negative error code.
 **/
static int iioutils_get_type(unsigned int *is_signed, unsigned int *bytes,
			     unsigned int *bits_used, unsigned int *shift,
			     uint64_t *mask, unsigned int *be,
			     const char *device_dir, int buffer_idx,
			     const char *name, const char *generic_name)
{
	FILE *sysfsfp;
	int ret;
	DIR *dp;
	char *scan_el_dir, *builtname, *builtname_generic, *filename = 0;
	char signchar, endianchar;
	unsigned padint;
	const struct dirent *ent;

	ret = asprintf(&scan_el_dir, FORMAT_SCAN_ELEMENTS_DIR, device_dir, buffer_idx);
	if (ret < 0)
		return -ENOMEM;

	ret = asprintf(&builtname, FORMAT_TYPE_FILE, name);
	if (ret < 0) {
		ret = -ENOMEM;
		goto error_free_scan_el_dir;
	}
	ret = asprintf(&builtname_generic, FORMAT_TYPE_FILE, generic_name);
	if (ret < 0) {
		ret = -ENOMEM;
		goto error_free_builtname;
	}

	dp = opendir(scan_el_dir);
	if (!dp) {
		ret = -errno;
		goto error_free_builtname_generic;
	}

	ret = -ENOENT;
	while (ent = readdir(dp), ent)
		if ((strcmp(builtname, ent->d_name) == 0) ||
		    (strcmp(builtname_generic, ent->d_name) == 0)) {
			ret = asprintf(&filename,
				       "%s/%s", scan_el_dir, ent->d_name);
			if (ret < 0) {
				ret = -ENOMEM;
				goto error_closedir;
			}

			sysfsfp = fopen(filename, "r");
			if (!sysfsfp) {
				ret = -errno;
				fprintf(stderr, "failed to open %s\n",
					filename);
				goto error_free_filename;
			}

			ret = fscanf(sysfsfp,
				     "%ce:%c%u/%u>>%u",
				     &endianchar,
				     &signchar,
				     bits_used,
				     &padint, shift);
			if (ret < 0) {
				ret = -errno;
				fprintf(stderr,
					"failed to pass scan type description\n");
				goto error_close_sysfsfp;
			} else if (ret != 5) {
				ret = -EIO;
				fprintf(stderr,
					"scan type description didn't match\n");
				goto error_close_sysfsfp;
			}

			*be = (endianchar == 'b');
			*bytes = padint / 8;
			if (*bits_used == 64)
				*mask = ~(0ULL);
			else
				*mask = (1ULL << *bits_used) - 1ULL;

			*is_signed = (signchar == 's');
			if (fclose(sysfsfp)) {
				ret = -errno;
				fprintf(stderr, "Failed to close %s\n",
					filename);
				goto error_free_filename;
			}

			sysfsfp = 0;
			free(filename);
			filename = 0;

			/*
			 * Avoid having a more generic entry overwriting
			 * the settings.
			 */
			if (strcmp(builtname, ent->d_name) == 0)
				break;
		}

error_close_sysfsfp:
	if (sysfsfp)
		if (fclose(sysfsfp))
			perror("iioutils_get_type(): Failed to close file");

error_free_filename:
	if (filename)
		free(filename);

error_closedir:
	if (closedir(dp) == -1)
		perror("iioutils_get_type(): Failed to close directory");

error_free_builtname_generic:
	free(builtname_generic);
error_free_builtname:
	free(builtname);
error_free_scan_el_dir:
	free(scan_el_dir);

	return ret;
}

/**
 * iioutils_get_param_float() - read a float value from a channel parameter
 * @output: output the float value
 * @param_name: the parameter name to read
 * @device_dir: the IIO device directory in sysfs
 * @name: the channel name
 * @generic_name: the channel type name
 *
 * Returns a value >= 0 on success, otherwise a negative error code.
 **/
int iioutils_get_param_float(float *output, const char *param_name,
			     const char *device_dir, const char *name,
			     const char *generic_name)
{
	FILE *sysfsfp;
	int ret;
	DIR *dp;
	char *builtname, *builtname_generic;
	char *filename = NULL;
	const struct dirent *ent;

	ret = asprintf(&builtname, "%s_%s", name, param_name);
	if (ret < 0)
		return -ENOMEM;

	ret = asprintf(&builtname_generic,
		       "%s_%s", generic_name, param_name);
	if (ret < 0) {
		ret = -ENOMEM;
		goto error_free_builtname;
	}

	dp = opendir(device_dir);
	if (!dp) {
		ret = -errno;
		goto error_free_builtname_generic;
	}

	ret = -ENOENT;
	while (ent = readdir(dp), ent)
		if ((strcmp(builtname, ent->d_name) == 0) ||
		    (strcmp(builtname_generic, ent->d_name) == 0)) {
			ret = asprintf(&filename,
				       "%s/%s", device_dir, ent->d_name);
			if (ret < 0) {
				ret = -ENOMEM;
				goto error_closedir;
			}

			sysfsfp = fopen(filename, "r");
			if (!sysfsfp) {
				ret = -errno;
				goto error_free_filename;
			}

			errno = 0;
			if (fscanf(sysfsfp, "%f", output) != 1)
				ret = errno ? -errno : -ENODATA;

			break;
		}
error_free_filename:
	if (filename)
		free(filename);

error_closedir:
	if (closedir(dp) == -1)
		perror("iioutils_get_param_float(): Failed to close directory");

error_free_builtname_generic:
	free(builtname_generic);
error_free_builtname:
	free(builtname);

	return ret;
}

/**
 * bsort_channel_array_by_index() - sort the array in index order
 * @ci_array: the iio_channel_info array to be sorted
 * @cnt: the amount of array elements
 **/

void bsort_channel_array_by_index(struct iio_channel_info *ci_array, int cnt)
{
	struct iio_channel_info temp;
	int x, y;

	for (x = 0; x < cnt; x++)
		for (y = 0; y < (cnt - 1); y++)
			if (ci_array[y].index > ci_array[y + 1].index) {
				temp = ci_array[y + 1];
				ci_array[y + 1] = ci_array[y];
				ci_array[y] = temp;
			}
}

/**
 * build_channel_array() - function to figure out what channels are present
 * @device_dir: the IIO device directory in sysfs
 * @buffer_idx: the IIO buffer for this channel array
 * @ci_array: output the resulting array of iio_channel_info
 * @counter: output the amount of array elements
 *
 * Returns 0 on success, otherwise a negative error code.
 **/
int build_channel_array(const char *device_dir, int buffer_idx,
			struct iio_channel_info **ci_array, int *counter)
{
	DIR *dp;
	FILE *sysfsfp;
	int count = 0, i;
	struct iio_channel_info *current;
	int ret;
	const struct dirent *ent;
	char *scan_el_dir;
	char *filename;

	*counter = 0;
	ret = asprintf(&scan_el_dir, FORMAT_SCAN_ELEMENTS_DIR, device_dir, buffer_idx);
	if (ret < 0)
		return -ENOMEM;

	dp = opendir(scan_el_dir);
	if (!dp) {
		ret = -errno;
		goto error_free_name;
	}

	while (ent = readdir(dp), ent)
		if (strcmp(ent->d_name + strlen(ent->d_name) - strlen("_en"),
			   "_en") == 0) {
			ret = asprintf(&filename,
				       "%s/%s", scan_el_dir, ent->d_name);
			if (ret < 0) {
				ret = -ENOMEM;
				goto error_close_dir;
			}

			sysfsfp = fopen(filename, "r");
			if (!sysfsfp) {
				ret = -errno;
				free(filename);
				goto error_close_dir;
			}

			errno = 0;
			if (fscanf(sysfsfp, "%i", &ret) != 1) {
				ret = errno ? -errno : -ENODATA;
				if (fclose(sysfsfp))
					perror("build_channel_array(): Failed to close file");

				free(filename);
				goto error_close_dir;
			}
			if (ret == 1)
				(*counter)++;

			if (fclose(sysfsfp)) {
				ret = -errno;
				free(filename);
				goto error_close_dir;
			}

			free(filename);
		}

	*ci_array = malloc(sizeof(**ci_array) * (*counter));
	if (!*ci_array) {
		ret = -ENOMEM;
		goto error_close_dir;
	}

	seekdir(dp, 0);
	while (ent = readdir(dp), ent) {
		if (strcmp(ent->d_name + strlen(ent->d_name) - strlen("_en"),
			   "_en") == 0) {
			int current_enabled = 0;

			current = &(*ci_array)[count++];
			ret = asprintf(&filename,
				       "%s/%s", scan_el_dir, ent->d_name);
			if (ret < 0) {
				ret = -ENOMEM;
				/* decrement count to avoid freeing name */
				count--;
				goto error_cleanup_array;
			}

			sysfsfp = fopen(filename, "r");
			if (!sysfsfp) {
				ret = -errno;
				free(filename);
				count--;
				goto error_cleanup_array;
			}

			errno = 0;
			if (fscanf(sysfsfp, "%i", &current_enabled) != 1) {
				ret = errno ? -errno : -ENODATA;
				free(filename);
				count--;
				goto error_cleanup_array;
			}

			if (fclose(sysfsfp)) {
				ret = -errno;
				free(filename);
				count--;
				goto error_cleanup_array;
			}

			if (!current_enabled) {
				free(filename);
				count--;
				continue;
			}

			current->scale = 1.0;
			current->offset = 0;
			current->name = strndup(ent->d_name,
						strlen(ent->d_name) -
						strlen("_en"));
			if (!current->name) {
				free(filename);
				ret = -ENOMEM;
				count--;
				goto error_cleanup_array;
			}

			/* Get the generic and specific name elements */
			ret = iioutils_break_up_name(current->name,
						     &current->generic_name);
			if (ret) {
				free(filename);
				free(current->name);
				count--;
				goto error_cleanup_array;
			}

			ret = asprintf(&filename,
				       "%s/%s_index",
				       scan_el_dir,
				       current->name);
			if (ret < 0) {
				free(filename);
				ret = -ENOMEM;
				goto error_cleanup_array;
			}

			sysfsfp = fopen(filename, "r");
			if (!sysfsfp) {
				ret = -errno;
				fprintf(stderr, "failed to open %s\n",
					filename);
				free(filename);
				goto error_cleanup_array;
			}

			errno = 0;
			if (fscanf(sysfsfp, "%u", &current->index) != 1) {
				ret = errno ? -errno : -ENODATA;
				if (fclose(sysfsfp))
					perror("build_channel_array(): Failed to close file");

				free(filename);
				goto error_cleanup_array;
			}

			if (fclose(sysfsfp)) {
				ret = -errno;
				free(filename);
				goto error_cleanup_array;
			}

			free(filename);
			/* Find the scale */
			ret = iioutils_get_param_float(&current->scale,
						       "scale",
						       device_dir,
						       current->name,
						       current->generic_name);
			if ((ret < 0) && (ret != -ENOENT))
				goto error_cleanup_array;

			ret = iioutils_get_param_float(&current->offset,
						       "offset",
						       device_dir,
						       current->name,
						       current->generic_name);
			if ((ret < 0) && (ret != -ENOENT))
				goto error_cleanup_array;

			ret = iioutils_get_type(&current->is_signed,
						&current->bytes,
						&current->bits_used,
						&current->shift,
						&current->mask,
						&current->be,
						device_dir,
						buffer_idx,
						current->name,
						current->generic_name);
			if (ret < 0)
				goto error_cleanup_array;
		}
	}

	if (closedir(dp) == -1) {
		ret = -errno;
		goto error_cleanup_array;
	}

	free(scan_el_dir);
	/* reorder so that the array is in index order */
	bsort_channel_array_by_index(*ci_array, *counter);

	return 0;

error_cleanup_array:
	for (i = count - 1;  i >= 0; i--) {
		free((*ci_array)[i].name);
		free((*ci_array)[i].generic_name);
	}
	free(*ci_array);
	*ci_array = NULL;
	*counter = 0;
error_close_dir:
	if (dp)
		if (closedir(dp) == -1)
			perror("build_channel_array(): Failed to close dir");

error_free_name:
	free(scan_el_dir);

	return ret;
}

static int calc_digits(int num)
{
	int count = 0;

	/* It takes a digit to represent zero */
	if (!num)
		return 1;

	while (num != 0) {
		num /= 10;
		count++;
	}

	return count;
}

/**
 * find_type_by_name() - function to match top level types by name
 * @name: top level type instance name
 * @type: the type of top level instance being searched
 *
 * Returns the device number of a matched IIO device on success, otherwise a
 * negative error code.
 * Typical types this is used for are device and trigger.
 **/
int find_type_by_name(const char *name, const char *type)
{
	const struct dirent *ent;
	int number, numstrlen, ret;

	FILE *namefp;
	DIR *dp;
	char thisname[IIO_MAX_NAME_LENGTH];
	char *filename;

	dp = opendir(iio_dir);
	if (!dp) {
		fprintf(stderr, "No industrialio devices available\n");
		return -ENODEV;
	}

	while (ent = readdir(dp), ent) {
		if (strcmp(ent->d_name, ".") != 0 &&
		    strcmp(ent->d_name, "..") != 0 &&
		    strlen(ent->d_name) > strlen(type) &&
		    strncmp(ent->d_name, type, strlen(type)) == 0) {
			errno = 0;
			ret = sscanf(ent->d_name + strlen(type), "%d", &number);
			if (ret < 0) {
				ret = -errno;
				fprintf(stderr,
					"failed to read element number\n");
				goto error_close_dir;
			} else if (ret != 1) {
				ret = -EIO;
				fprintf(stderr,
					"failed to match element number\n");
				goto error_close_dir;
			}

			numstrlen = calc_digits(number);
			/* verify the next character is not a colon */
			if (strncmp(ent->d_name + strlen(type) + numstrlen,
			    ":", 1) != 0) {
				filename = malloc(strlen(iio_dir) + strlen(type)
						  + numstrlen + 6);
				if (!filename) {
					ret = -ENOMEM;
					goto error_close_dir;
				}

				ret = sprintf(filename, "%s%s%d/name", iio_dir,
					      type, number);
				if (ret < 0) {
					free(filename);
					goto error_close_dir;
				}

				namefp = fopen(filename, "r");
				if (!namefp) {
					free(filename);
					continue;
				}

				free(filename);
				errno = 0;
				if (fscanf(namefp, "%s", thisname) != 1) {
					ret = errno ? -errno : -ENODATA;
					goto error_close_dir;
				}

				if (fclose(namefp)) {
					ret = -errno;
					goto error_close_dir;
				}

				if (strcmp(name, thisname) == 0) {
					if (closedir(dp) == -1)
						return -errno;

					return number;
				}
			}
		}
	}
	if (closedir(dp) == -1)
		return -errno;

	return -ENODEV;

error_close_dir:
	if (closedir(dp) == -1)
		perror("find_type_by_name(): Failed to close directory");

	return ret;
}

static int _write_sysfs_int(const char *filename, const char *basedir, int val,
			    int verify)
{
	int ret = 0;
	FILE *sysfsfp;
	int test;
	char *temp = malloc(strlen(basedir) + strlen(filename) + 2);

	if (!temp)
		return -ENOMEM;

	ret = sprintf(temp, "%s/%s", basedir, filename);
	if (ret < 0)
		goto error_free;

	sysfsfp = fopen(temp, "w");
	if (!sysfsfp) {
		ret = -errno;
		fprintf(stderr, "failed to open %s\n", temp);
		goto error_free;
	}

	ret = fprintf(sysfsfp, "%d", val);
	if (ret < 0) {
		if (fclose(sysfsfp))
			perror("_write_sysfs_int(): Failed to close dir");

		goto error_free;
	}

	if (fclose(sysfsfp)) {
		ret = -errno;
		goto error_free;
	}

	if (verify) {
		sysfsfp = fopen(temp, "r");
		if (!sysfsfp) {
			ret = -errno;
			fprintf(stderr, "failed to open %s\n", temp);
			goto error_free;
		}

		if (fscanf(sysfsfp, "%d", &test) != 1) {
			ret = errno ? -errno : -ENODATA;
			if (fclose(sysfsfp))
				perror("_write_sysfs_int(): Failed to close dir");

			goto error_free;
		}

		if (fclose(sysfsfp)) {
			ret = -errno;
			goto error_free;
		}

		if (test != val) {
			fprintf(stderr,
				"Possible failure in int write %d to %s/%s\n",
				val, basedir, filename);
			ret = -1;
		}
	}

error_free:
	free(temp);
	return ret;
}

/**
 * write_sysfs_int() - write an integer value to a sysfs file
 * @filename: name of the file to write to
 * @basedir: the sysfs directory in which the file is to be found
 * @val: integer value to write to file
 *
 * Returns a value >= 0 on success, otherwise a negative error code.
 **/
int write_sysfs_int(const char *filename, const char *basedir, int val)
{
	return _write_sysfs_int(filename, basedir, val, 0);
}

/**
 * write_sysfs_int_and_verify() - write an integer value to a sysfs file
 *				  and verify
 * @filename: name of the file to write to
 * @basedir: the sysfs directory in which the file is to be found
 * @val: integer value to write to file
 *
 * Returns a value >= 0 on success, otherwise a negative error code.
 **/
int write_sysfs_int_and_verify(const char *filename, const char *basedir,
			       int val)
{
	return _write_sysfs_int(filename, basedir, val, 1);
}

static int _write_sysfs_string(const char *filename, const char *basedir,
			       const char *val, int verify)
{
	int ret = 0;
	FILE  *sysfsfp;
	char *temp = malloc(strlen(basedir) + strlen(filename) + 2);

	if (!temp) {
		fprintf(stderr, "Memory allocation failed\n");
		return -ENOMEM;
	}

	ret = sprintf(temp, "%s/%s", basedir, filename);
	if (ret < 0)
		goto error_free;

	sysfsfp = fopen(temp, "w");
	if (!sysfsfp) {
		ret = -errno;
		fprintf(stderr, "Could not open %s\n", temp);
		goto error_free;
	}

	ret = fprintf(sysfsfp, "%s", val);
	if (ret < 0) {
		if (fclose(sysfsfp))
			perror("_write_sysfs_string(): Failed to close dir");

		goto error_free;
	}

	if (fclose(sysfsfp)) {
		ret = -errno;
		goto error_free;
	}

	if (verify) {
		sysfsfp = fopen(temp, "r");
		if (!sysfsfp) {
			ret = -errno;
			fprintf(stderr, "Could not open file to verify\n");
			goto error_free;
		}

		if (fscanf(sysfsfp, "%s", temp) != 1) {
			ret = errno ? -errno : -ENODATA;
			if (fclose(sysfsfp))
				perror("_write_sysfs_string(): Failed to close dir");

			goto error_free;
		}

		if (fclose(sysfsfp)) {
			ret = -errno;
			goto error_free;
		}

		if (strcmp(temp, val) != 0) {
			fprintf(stderr,
				"Possible failure in string write of %s "
				"Should be %s written to %s/%s\n", temp, val,
				basedir, filename);
			ret = -1;
		}
	}

error_free:
	free(temp);

	return ret;
}

/**
 * write_sysfs_string_and_verify() - string write, readback and verify
 * @filename: name of file to write to
 * @basedir: the sysfs directory in which the file is to be found
 * @val: the string to write
 *
 * Returns a value >= 0 on success, otherwise a negative error code.
 **/
int write_sysfs_string_and_verify(const char *filename, const char *basedir,
				  const char *val)
{
	return _write_sysfs_string(filename, basedir, val, 1);
}

/**
 * write_sysfs_string() - write string to a sysfs file
 * @filename: name of file to write to
 * @basedir: the sysfs directory in which the file is to be found
 * @val: the string to write
 *
 * Returns a value >= 0 on success, otherwise a negative error code.
 **/
int write_sysfs_string(const char *filename, const char *basedir,
		       const char *val)
{
	return _write_sysfs_string(filename, basedir, val, 0);
}

/**
 * read_sysfs_posint() - read an integer value from file
 * @filename: name of file to read from
 * @basedir: the sysfs directory in which the file is to be found
 *
 * Returns the read integer value >= 0 on success, otherwise a negative error
 * code.
 **/
int read_sysfs_posint(const char *filename, const char *basedir)
{
	int ret;
	FILE  *sysfsfp;
	char *temp = malloc(strlen(basedir) + strlen(filename) + 2);

	if (!temp) {
		fprintf(stderr, "Memory allocation failed");
		return -ENOMEM;
	}

	ret = sprintf(temp, "%s/%s", basedir, filename);
	if (ret < 0)
		goto error_free;

	sysfsfp = fopen(temp, "r");
	if (!sysfsfp) {
		ret = -errno;
		goto error_free;
	}

	errno = 0;
	if (fscanf(sysfsfp, "%d\n", &ret) != 1) {
		ret = errno ? -errno : -ENODATA;
		if (fclose(sysfsfp))
			perror("read_sysfs_posint(): Failed to close dir");

		goto error_free;
	}

	if (fclose(sysfsfp))
		ret = -errno;

error_free:
	free(temp);

	return ret;
}

/**
 * read_sysfs_float() - read a float value from file
 * @filename: name of file to read from
 * @basedir: the sysfs directory in which the file is to be found
 * @val: output the read float value
 *
 * Returns a value >= 0 on success, otherwise a negative error code.
 **/
int read_sysfs_float(const char *filename, const char *basedir, float *val)
{
	int ret = 0;
	FILE  *sysfsfp;
	char *temp = malloc(strlen(basedir) + strlen(filename) + 2);

	if (!temp) {
		fprintf(stderr, "Memory allocation failed");
		return -ENOMEM;
	}

	ret = sprintf(temp, "%s/%s", basedir, filename);
	if (ret < 0)
		goto error_free;

	sysfsfp = fopen(temp, "r");
	if (!sysfsfp) {
		ret = -errno;
		goto error_free;
	}

	errno = 0;
	if (fscanf(sysfsfp, "%f\n", val) != 1) {
		ret = errno ? -errno : -ENODATA;
		if (fclose(sysfsfp))
			perror("read_sysfs_float(): Failed to close dir");

		goto error_free;
	}

	if (fclose(sysfsfp))
		ret = -errno;

error_free:
	free(temp);

	return ret;
}

/**
 * read_sysfs_string() - read a string from file
 * @filename: name of file to read from
 * @basedir: the sysfs directory in which the file is to be found
 * @str: output the read string
 *
 * Returns a value >= 0 on success, otherwise a negative error code.
 **/
int read_sysfs_string(const char *filename, const char *basedir, char *str)
{
	int ret = 0;
	FILE  *sysfsfp;
	char *temp = malloc(strlen(basedir) + strlen(filename) + 2);

	if (!temp) {
		fprintf(stderr, "Memory allocation failed");
		return -ENOMEM;
	}

	ret = sprintf(temp, "%s/%s", basedir, filename);
	if (ret < 0)
		goto error_free;

	sysfsfp = fopen(temp, "r");
	if (!sysfsfp) {
		ret = -errno;
		goto error_free;
	}

	errno = 0;
	if (fscanf(sysfsfp, "%s\n", str) != 1) {
		ret = errno ? -errno : -ENODATA;
		if (fclose(sysfsfp))
			perror("read_sysfs_string(): Failed to close dir");

		goto error_free;
	}

	if (fclose(sysfsfp))
		ret = -errno;

error_free:
	free(temp);

	return ret;
}