Date: Sat, 27 Jul 2013 10:12:08 +0300 From: Andriy Gapon <avg@FreeBSD.org> To: Mark Johnston <markj@FreeBSD.org> Cc: freebsd-dtrace@FreeBSD.org Subject: Re: [RFC] reworking FreeBSD's SDT implementation Message-ID: <51F372C8.1000107@FreeBSD.org> In-Reply-To: <20130727022656.GB67227@raichu> 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> <20130727022656.GB67227@raichu>
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on 27/07/2013 05:26 Mark Johnston said the following: > 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? Hmm, I didn't think about this problem in advance... Having looked around I think that it should be possible to handle this situation in a way similar to watchdog_list. watchdog(9) documents how that works. Of course, all handlers will have to be careful to not override error if it's already set. -- Andriy Gapon
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