Date: Fri, 26 Jul 2013 22:26:56 -0400 From: Mark Johnston <markj@freebsd.org> To: Andriy Gapon <avg@FreeBSD.org> Cc: freebsd-dtrace@FreeBSD.org Subject: Re: [RFC] reworking FreeBSD's SDT implementation Message-ID: <20130727022656.GB67227@raichu> In-Reply-To: <51F14150.7000509@FreeBSD.org> References: <20130703041023.GA82673@raichu> <20130711024500.GA67976@raichu> <20130711210215.GB7506@gmail.com> <20130713234200.GA40803@raichu> <20130714075634.GC2832@gmail.com> <20130722022811.GA14288@raichu> <51F14150.7000509@FreeBSD.org>
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On Thu, Jul 25, 2013 at 06:16:32PM +0300, Andriy Gapon wrote: > on 22/07/2013 05:28 markj@freebsd.org said the following: > > http://people.freebsd.org/~markj/patches/sdt-module-info/20130721-sdt-module-info.diff > > Mark, > > this is a minor suggestion only partially related to your patch. > I think that it would be nice if module loading and unloading events were posted > via EVENTHANDLER(9) mechanism. Then instead of introducing yet more DTrace > related hooks in the kernel code, DTrace modules could just subscribe to those > events. Also, those events could be potentially useful to other consumers > beyond DTrace. > What do you think? Hm, now that I look at this, I'm not sure if it can work. The unload hooks need to be able to veto a module unload in the case that one of its probes is enabled. This is done by checking whether lf->nenabled > 0, and it needs to be done with the dtrace lock held to prevent races. I've done this by having the unload hooks return a non-zero value if there are probes enabled, but EVENTHANDLER(9) doesn't give me a way to look at a handler's return value. Do you see a way to get around this? Thanks, -Mark
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