Re: General flags to turn things off (getrandom, pid lookup, etc)

One Thousand Gnomes [off-list ref] writes:

quoted

Andy you seem to be arguing here for two system calls.
get_urandom() and get_random().

Where get_urandom only blocks if there is not enough starting entropy,
and get_random(GRND_RANDOM) blocks if there is currently not enough
entropy.

That would allow -ENOSYS to be the right return value and it would
simply things for everyone.

So you replace the "no file handle" special case with the "unsupported or
disabled syscall" special case, which is even harder to test.

Interfaces have failure modes. People who can't deal with that shouldn't
be writing code that does anything important in languages which don't
handle it for them.

Perhaps I misread the earlier conversation but it what I have read of
this discussion people want to disable some of get_random() modes with
seccomp.  Today get_random does not have any failure codes define except
-ENOSYS.

get_random(0) succeeding and get_random(GRND_RANDOM) returning -ENOSYS
has every chance of causing applications to legitimately assume the
get_random system call is not available in any mode.

So the code either needs a defined error code for bad flags (-EINVAL) or
we need to split the syscall in two.  Now that I think about it having
the seccomp filter return -EINVAL if it doesn't like the parameter is
better that splitting a syscall.  Presumably that is what
get_random(UNSUPPORTED_FLAG) returns.

Eric