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From: | Denis V. Lunev |
Subject: | Re: [Qemu-devel] What's the intended use of log.h logging? |
Date: | Fri, 16 Oct 2015 16:38:44 +0300 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.3.0 |
On 10/16/2015 04:00 PM, Paolo Bonzini wrote:
On 16/10/2015 14:54, Peter Maydell wrote:On 16 October 2015 at 13:48, Paolo Bonzini <address@hidden> wrote:On 16/10/2015 14:33, Markus Armbruster wrote:Looks like this is basically TCG with a couple of random LOG_UNIMP and LOG_GUEST_ERROR thrown in. It's definitely not a general purpose QEMU log in its current state.I think these could become error_report.No; it's important not to print these unless the user really asked for them (especially the GUEST_ERROR) kind. Otherwise it's (potentially quite a lot of) unnecessary noise.I guess it depends then. If the unimplemented feature is in all likelihood a showstopper (e.g. setend) it should be unconditionally enabled, I think.Some others (e.g. LOG_IOPORT) can be removed. LOG_MMU seems to be mostly a ppc thing, could also become a tracepoint. Likewise for LOG_PCALL and perhaps LOG_INT.It's also very useful to be able to enable whole *classes* of tracing (like "tell me whenever my guest OS does something dumb"); does the tracepoint code have any support for this?That's part of what I mentioned in my message ("add some functionality to enable tracepoints more easily"). It would be great to have something like "-d trace:scsi_*" on the command line, integrated with qemu-log. So perhaps the place of qemu-log is as a replacement for the stderr tracing backend? Paolo
The motivation for the patchset is simple. These messages will be quite useful to understand how things are going. We do not think about automatic parsing of that logs at all. They should be human-readable for us to understand the problem. In general, we should have "normal" locking engine. Here I mean a non-blocking facility, which should allow to place arbitrary log message preserving order of that message in which events have been happen. In general, this is possible through lockless ring-buffer and a flush thread. Yes, messages could be lost if this is noted to the log. I am a bit old-fashioned with this approach, sorry. This information is at least necessary to guess what operations were performed with a VM from outside using conventional interfaces. Thus my approach to the topic is simple. I'd like to put minimal information at the moment using current API for 2.5 and expect this merged if possible, For 2.6 we will replace the engine with one I have described above. From my point of view this work should not start new sub-system but slowly evolve current one. All bits here a a bit technical without much usage details, but this is something which should be discussed. With an effective backend (which does not contradict to the current implementation) more could be allowed to be logged. Tracepoints, in general, are designated for the debugging. Logging is something for post-ship analysis from the customer report and speaking about [commercially] supported product running in _production_ you will not be able either to access customer's host or even customer's network. Den
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