[Toybox] [PATCH] Make find -exec + obey ARG_MAX just like xargs.

[enh]

On Thu, Nov 23, 2017 at 4:37 AM, Rob Landley <rob at landley.net> wrote:
> Sorry for the delay, the downside of traveling for work is you wind up
> doing rather a lot of work.
>
> (We've made it through the investor meetings and back to GPS. The
> milisecond slips were due to codephase wrap but the fix that fits with
> the design is to adjust the length of the nominal second independently
> for each satellite rather than to try to adjust the time consumed by
> each bit even THOUGH we already have bits that don't take 20 nominal
> miliseconds due to clock skew between the antenna sampling clock and the
> satellite's transmission rate eventually resulting in a period
> adjustment. And no, it's not just doppler shift from the orbit, all
> these clocks vary with temperature _even_when_thermally_stabilized_ to
> make this stuff a giant pile of exceptions and wraparounds...)
>
> On 11/16/2017 04:20 PM, enh wrote:
>> correspondingly, i've made bionic's _SC_ARG_MAX return a constant
>> 128KiB again.
>
> Which is cool, and what Linus said to do, but having environment space
> subtract from that 128k means you can easily get into a situation where
> you haven't even got space for one argument. (Although we seem to always
> do one and only care we went "tilt" afterwards, so it shouldn't get into
> a starvation situation I think.)
>
> I suspect we should give the environment space its own 128k, and only
> trim the argument space if environment eats more than that? But this is
> back into "heuristics not matching what kernel is actually doing" land
> again. (I really dowanna bother Linus for a second opinion...)
>
>> we might want to actually just hard-code 128KiB for both
>> find and xargs, but making find and xargs the same first seemed like a
>> good idea regardless.
>
> We have Word From On High that 128k for _SC_ARG_MAX is ok. (Although
> will portability to the Fuchsia kernel ever matter?) The problem is
> _SC_ARG_MAX isn't _SC_ENV_MAX, and if the relationship between argument
> space and environment space is mentioned by posix I've missed where.
>
>> let me know if you want me to send a "make find/xargs use a constant"
>> patch too (glibc removed ARG_MAX, so i think we'd want a #ifndef in
>> portability.h).
>
> Meh, glibc is insane.
>
> I might want to have a lib/*.c function to say "how big can I exec" and
> have them both use it, but we need to answer that question properly first...

yeah, this is what led me to suggest this patch: it fixes the one
problem we've actually seen in practice, and hopefully we'll have a
clearer idea of what a better fix looks like when (if) we get a bug
report against this implementation. because none of the choices really
seems particularly appealing...

> Rob



-- 
Elliott Hughes - http://who/enh - http://jessies.org/~enh/
Android native code/tools questions? Mail me/drop by/add me as a reviewer.