Re: [PATCH v18 2/5] random: add vgetrandom_alloc() syscall

[Thomas Gleixner <tglx@linutronix.de>]

Jason!

On Thu, Jun 20 2024 at 14:18, Jason A. Donenfeld wrote:
> On Wed, Jun 19, 2024 at 07:13:26PM -0700, Aleksa Sarai wrote:
>> Then again, I guess since libc is planned to be the primary user,
>> creating a new syscall in a decade if necessary is probably not that big
>> of an issue.
>
> I'm not sure going the whole big struct thing is really necessary, and
> for an additional reason: this is only meant to be used with the vDSO
> function, which is also coupled with the kernel. It doesn't return
> information that's made to be used (or allowed to be used) anywhere
> else. So both the vdso code and the syscall code are part of the same
> basic thing that will evolve together. So I'm not convinced extensible
> struct really makes sense for this, as neat as it is.
>
> If there's wide consensus that it's desirable, in contrast to what I'm
> saying, I'm not vehemently opposed to it and could do it, but it just
> seems like massive overkill and not at all necessary. Things are
> intentionally as simple and straightforward as can be.

Right, but the problem is that this is a syscall, so people are free to
explore it even without the vdso part. Now when you want to change it
later then you are caught in the no-regression trap.

So making it extensible with backwards compability in place (add the
unused flag field and check for 0) will allow you to expand without
breaking users.

Thanks,

        tglx