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Message-ID: <20200415160139.GE11469@brightrain.aerifal.cx>
Date: Wed, 15 Apr 2020 12:01:39 -0400
From: Rich Felker <dalias@...c.org>
To: musl@...ts.openwall.com, Florian Weimer <fw@...eb.enyo.de>,
Norbert Lange <nolange79@...il.com>
Subject: Re: [BUG] sysconf implementing _SC_NPROCESSORS_(CONF|ONLN)
incorrectly
On Wed, Apr 15, 2020 at 12:04:43PM +0200, Szabolcs Nagy wrote:
> * Norbert Lange <nolange79@...il.com> [2020-04-15 11:57:16 +0200]:
> > I can't comment on whether glibc should be emulated. The point I am trying
> > to make is that it might be better to let the compilation fail by default,
> > or not provide the function at all.
> >
> > The implementation right now doesn't seem sufficient (to put it midly) and
> > it prevents detection and automatic fallbacks. For example trace-cmd would
> > do this, and would work nicely - but instead it will gets musls
> > implementation that's defeated by setting an affinity mask.
>
> the point is that the glibc implementation is not sufficient either.
>
> you don't get what you think you get as a result so you better off
> to just always do the fallback.
>
> identifying musl via a macro would be extremely bad in this case
> since we are discussing to change the implementation and the
> macro would not reflect that so a wrong default would be baked
> into the source (which shows why it is a good idea not to provide
> such a macro at all: most developers dont understand how to use
> such macros and by now there would be a lot of broken musl
> workarounds that are not relevant to the latest musl version).
Note that this could be represented by the sort of macro exposure I
want to propose on libc-coord: not __MUSL__ but something like
_EXT_SC_...NPROC_REFLECTS_RESOURCE_CONSTRAINTS. Of course then it
would document a specific permanent (without redefining the _SC_*
macros to different values for a new one) behavior, so this may not be
a good choice. As a worst case the behavior could be documented to the
application via another sysconf variable. :-P
Rich
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