source: azure_iot_hub/trunk/musl-1.1.18/src/misc/realpath.c@ 388

#include <stdlib.h>
#include <limits.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include <unistd.h>
#include <string.h>
#include "syscall.h"

void __procfdname(char *, unsigned);

char *realpath(const char *restrict filename, char *restrict resolved)
{
        int fd;
        ssize_t r;
        struct stat st1, st2;
        char buf[15+3*sizeof(int)];
        char tmp[PATH_MAX];

        if (!filename) {
                errno = EINVAL;
                return 0;
        }

        fd = sys_open(filename, O_PATH|O_NONBLOCK|O_CLOEXEC);
        if (fd < 0) return 0;
        __procfdname(buf, fd);

        r = readlink(buf, tmp, sizeof tmp - 1);
        if (r < 0) goto err;
        tmp[r] = 0;

        fstat(fd, &st1);
        r = stat(tmp, &st2);
        if (r<0 || st1.st_dev != st2.st_dev || st1.st_ino != st2.st_ino) {
                if (!r) errno = ELOOP;
                goto err;
        }

        __syscall(SYS_close, fd);
        return resolved ? strcpy(resolved, tmp) : strdup(tmp);
err:
        __syscall(SYS_close, fd);
        return 0;
}