source: azure_iot_hub/trunk/musl-1.1.18/src/stat/fchmodat.c@ 388

#include <sys/stat.h>
#include <fcntl.h>
#include <errno.h>
#include "syscall.h"

void __procfdname(char *, unsigned);

int fchmodat(int fd, const char *path, mode_t mode, int flag)
{
        if (!flag) return syscall(SYS_fchmodat, fd, path, mode, flag);

        if (flag != AT_SYMLINK_NOFOLLOW)
                return __syscall_ret(-EINVAL);

        struct stat st;
        int ret, fd2;
        char proc[15+3*sizeof(int)];

        if ((ret = __syscall(SYS_fstatat, fd, path, &st, flag)))
                return __syscall_ret(ret);
        if (S_ISLNK(st.st_mode))
                return __syscall_ret(-EOPNOTSUPP);

        if ((fd2 = __syscall(SYS_openat, fd, path, O_RDONLY|O_PATH|O_NOFOLLOW|O_NOCTTY|O_CLOEXEC)) < 0) {
                if (fd2 == -ELOOP)
                        return __syscall_ret(-EOPNOTSUPP);
                return __syscall_ret(fd2);
        }

        __procfdname(proc, fd2);
        ret = __syscall(SYS_fstatat, AT_FDCWD, proc, &st, 0);
        if (!ret) {
                if (S_ISLNK(st.st_mode)) ret = -EOPNOTSUPP;
                else ret = __syscall(SYS_fchmodat, AT_FDCWD, proc, mode);
        }

        __syscall(SYS_close, fd2);
        return __syscall_ret(ret);
}