No, eaccess is NOT portable. Maybe we should find solution in libc. In musl libc, eaccess is define as: euidaccess.c ``` #define _GNU_SOURCE #include <unistd.h> #include <fcntl.h> #include "libc.h" int euidaccess(const char *filename, int amode) { return faccessat(AT_FDCWD, filename, amode, AT_EACCESS); } weak_alias(euidaccess, eaccess); ``` faccessat.c: ``` #include <unistd.h> #include <fcntl.h> #include <sys/wait.h> #include "syscall.h" #include "pthread_impl.h" struct ctx { int fd; const char *filename; int amode; int p; }; static int checker(void *p) { struct ctx *c = p; int ret; if (__syscall(SYS_setregid, __syscall(SYS_getegid), -1) || __syscall(SYS_setreuid, __syscall(SYS_geteuid), -1)) __syscall(SYS_exit, 1); ret = __syscall(SYS_faccessat, c->fd, c->filename, c->amode, 0); __syscall(SYS_write, c->p, &ret, sizeof ret); return 0; } int faccessat(int fd, const char *filename, int amode, int flag) { if (!flag || (flag==AT_EACCESS && getuid()==geteuid() && getgid()==getegid())) return syscall(SYS_faccessat, fd, filename, amode, flag); if (flag != AT_EACCESS) return __syscall_ret(-EINVAL); char stack[1024]; sigset_t set; pid_t pid; int status; int ret, p[2]; if (pipe2(p, O_CLOEXEC)) return __syscall_ret(-EBUSY); struct ctx c = { .fd = fd, .filename = filename, .amode = amode, .p = p[1] }; __block_all_sigs(&set); pid = __clone(checker, stack+sizeof stack, 0, &c); __syscall(SYS_close, p[1]); if (pid<0 || __syscall(SYS_read, p[0], &ret, sizeof ret) != sizeof(ret)) ret = -EBUSY; __syscall(SYS_close, p[0]); __syscall(SYS_wait4, pid, &status, __WCLONE, 0); __restore_sigs(&set); return __syscall_ret(ret); } ``` So, it calls clone to run checker. But is `clone` a good way? (Some system may strict clone syscall) Do you have other ways? Can we just change `unixTempFileDir` to really create a temporary file to check the directory is writable?