Date: Thu, 10 Jun 2010 10:18:01 +0200 From: Gary Jennejohn <gljennjohn@googlemail.com> To: Garrett Cooper <yaneurabeya@gmail.com> Cc: Kostik Belousov <kostikbel@gmail.com>, freebsd-hackers@freebsd.org, Bakulin <webmaster@kibab.com>, Ilya Subject: Re: GSoC: registration of optional kernel features via sysctl: a question to the community Message-ID: <20100610101801.742fac25@ernst.jennejohn.org> In-Reply-To: <A4C894EA-8039-459B-B4C8-8F7CC98421F8@gmail.com> References: <20100609121453.095d92b4@kibab.com> <4C0F9394.9030202@dataix.net> <20100609132543.GI83316@deviant.kiev.zoral.com.ua> <A4C894EA-8039-459B-B4C8-8F7CC98421F8@gmail.com>
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On Wed, 9 Jun 2010 10:12:54 -0700 Garrett Cooper <yaneurabeya@gmail.com> wrote: > On Jun 9, 2010, at 6:25 AM, Kostik Belousov wrote: > > > On Wed, Jun 09, 2010 at 09:13:56AM -0400, jhell wrote: > >> On 06/09/2010 04:14, Ilya Bakulin wrote: > >>> Hi hackers! > >>> > >>> While discussing my project's implementation details with my mentor, > >>> Alexander Leidinger, we've found that one of the ideas needs to be discussed with community, > >>> to find out possible use cases. > >>> That is, if it should be possible to spoof non-existing features. For > >>> example, if currently running kernel doesn't support FreeBSD 5.0 compat > >>> layer, "kern.features.compat_freebsd5" will be absent when querying > >>> features list. The question is -- are there any cases when we want > >>> "kern.features.compat_freebsd5" be present? If some feature is not in > >>> kernel, then presenting its existence to the userland is useless > >>> and may be even harmful, if, for example, some application relies on this feature. > >>> Or there are some scenarios where such cheat is useful? > >>> > >> > >> I can not think of any viable reason why one would want to "spoof" this > >> when it is not available. > > Many ports are doing wrong thing there, checking for run-time features at > > the build-time, turning on/off some functionality depending on its > > presence on the build host. > > It's present in the ports Makefiles as well as in many autoconf scripts. It's bad because it causes problems with cross-build and other related scenarios, where you can't assume that the host system is going to match the target system. > I don't find one single file in the ports tree which uses kern.features. But I just checked what's in the tree, not what may be in the ports themselves, i.e., I didn't extract/configure any ports. -- Gary Jennejohn
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