Date: Tue, 26 Mar 2019 12:23:34 -0400 From: Jonathan Rajotte-Julien <jonathan.rajotte-julien@...icios.com> To: musl@...ts.openwall.com, Michael Jeanson <mjeanson@...icios.com>, Richard Purdie <richard.purdie@...uxfoundation.org>, Mathieu Desnoyers <mathieu.desnoyers@...icios.com> Subject: Re: sysconf(_SC_NPROCESSORS_CONF) returns the wrong value Hi Szabolcs, > i think we need to know why does a process care if musl returns > the wrong number? or what are the valid uses of such a number? > (there are heterogeous systems like arm big-little, numa systems > with many sockets, containers, virtualization,.. how deep may a > user process need to go down in this rabbit hole?) Does the answers from Mathieu Desnoyers  and Florian Weimer  fit the bill?  https://www.openwall.com/lists/musl/2019/03/16/3  https://www.openwall.com/lists/musl/2019/03/19/1 > > note that most of /sys/devices/system/cpu/* is documented under > Documentation/ABI/testing in linux, not in Documentation/ABI/stable > and the format is not detailed, and some apis (e.g. /proc/cpuinfo) > are known to be different on android (and grsec?) kernels it may > be unmounted during early boot or in chroots, so sysfs parsing is > only done when really necessary. For what it's worth, uclibc and uclibc-ng seem to iterate over /sys/devices/system/cpu/* and fallback on online calculation if necessary. https://cgit.uclibc-ng.org/cgi/cgit/uclibc-ng.git/tree/libc/unistd/sysconf.c#n102 In the mean time, we implemented a fallback similar to this when we do not "know" the libc used (since musl does not come with __musl__, I read the reasons why, no need to discuss this). Not sure of the direction musl should take but I strongly believe that the behaviour regarding _SC_NPROCESSORS_CONF is not the appropriate one. Cheers -- Jonathan Rajotte-Julien EfficiOS
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