// 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;

                        fclose(sysfsfp);
                        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");
                        free(filename);
                        if (!sysfsfp) {
                                ret = -errno;
                                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");

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

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

                }

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

        rewinddir(dp);
        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");
                        free(filename);
                        if (!sysfsfp) {
                                ret = -errno;
                                count--;
                                goto error_cleanup_array;
                        }

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

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

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

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

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

                        sysfsfp = fopen(filename, "r");
                        free(filename);
                        if (!sysfsfp) {
                                ret = -errno;
                                fprintf(stderr, "failed to open %s/%s_index\n",
                                        scan_el_dir, current->name);
                                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");

                                goto error_cleanup_array;
                        }

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

                        /* 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;
}