Aleksa Sarai <cyphar@xxxxxxxxxx> writes: >> In fairness, this is how statx works and statx does this to not require >> syscall retries to figure out what flags the current kernel supports and >> instead defers that to stx_mask. >> >> However, I think verifying the value is slightly less fragile -- as long >> as we get a cheap way for userspace to check what flags are supported >> (such as CHECK_FIELDS[1]). It would kind of suck if userspace would have >> to do 50 syscalls to figure out what request_mask values are valid. > > Unfortunately, we probably need to find a different way to do > CHECK_FIELDS for extensible-struct ioctls because CHECK_FIELDS uses the > top bit in a u64 but we can't set a size that large with ioctl > numbers... Add a separate PIDFD_GET_VALID_REQUEST_MASK ioctl()? But then I'm bad at designing interfaces... jon
