setPermissionsPosix

fn setPermissionsPosix(fd: posix.fd_t, mode: posix.mode_t) File.SetPermissionsError!void {
    comptime assert(have_fchmod);
    const syscall: Syscall = try .start();
    while (true) {
        switch (posix.errno(posix.system.fchmod(fd, mode))) {
            .SUCCESS => return syscall.finish(),
            .INTR => {
                try syscall.checkCancel();
                continue;
            },
            else => |e| {
                syscall.finish();
                switch (e) {
                    .BADF => |err| return errnoBug(err),
                    .FAULT => |err| return errnoBug(err),
                    .INVAL => |err| return errnoBug(err),
                    .ACCES => return error.AccessDenied,
                    .IO => return error.InputOutput,
                    .LOOP => return error.SymLinkLoop,
                    .NOENT => return error.FileNotFound,
                    .NOMEM => return error.SystemResources,
                    .NOTDIR => return error.FileNotFound,
                    .PERM => return error.PermissionDenied,
                    .ROFS => return error.ReadOnlyFileSystem,
                    else => |err| return posix.unexpectedErrno(err),
                }
            },
        }
    }
}