Date: Fri, 29 Jun 2007 12:00:17 +0100 (BST) From: Robert Watson <rwatson@FreeBSD.org> To: Howard Su <howard0su@gmail.com> Cc: current@freebsd.org Subject: Re: concept prove patch for ktrace output to all file types Message-ID: <20070629115820.N50751@fledge.watson.org> In-Reply-To: <f126fae00706290317qbd1e74aocaa482f56df842e9@mail.gmail.com> References: <f126fae00706270934h3e39e33avaa686aa2c12b72c6@mail.gmail.com> <20070628094219.W9286@fledge.watson.org> <f126fae00706290317qbd1e74aocaa482f56df842e9@mail.gmail.com>
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On Fri, 29 Jun 2007, Howard Su wrote: > On 6/28/07, Robert Watson <rwatson@freebsd.org> wrote: >> >> What happens to processes associated with the same or other ktrace sessions >> if one ktrace session stalls due to a fifo or pipe buffer filling? > > I don't think my patch will bring the new problem here. Original, we write > to disk still be blocked due to some things like disk busy, etc. > > If my reading is right, ktrace use two way to submit request. ktr_enqueue > will put the request into a queue if it is not safe to enter VFS. > ktr_submitrequest will be used to commit record to disk immediately. in my > case, blocking will be safe there. > > The issue about losting some recording to fifo blocking. I don't think we > can solve that in the kernel. It is userland code's responsiblity to read it > to avoid losting data. The question I'm asking is most interesting with respect to independent ktrace sessions, potentially associated with different users. If a tracing app can't keep up with the app it's tracing, that's quite a different case from all system tracing breaking because one tracing app can't keep up with its particular target. In a casual analysis, it looks like if one fifo blocks, then all tracing across the system is stuck waiting on that fifo to unblock? Robert N M Watson Computer Laboratory University of Cambridge
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