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(No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 5966A3DE31; Thu, 15 Aug 2019 17:34:00 +0000 (UTC) Received: from [10.18.17.169] (dhcp-17-169.bos.redhat.com [10.18.17.169]) by smtp.corp.redhat.com (Postfix) with ESMTP id A224417AAA; Thu, 15 Aug 2019 17:33:54 +0000 (UTC) To: Kevin Wolf References: <20190814100735.24234-1-vsementsov@virtuozzo.com> <20190814100735.24234-3-vsementsov@virtuozzo.com> <3eded188-0161-d494-194c-9d67da644eb1@redhat.com> <20190815104928.GC7415@linux.fritz.box> <9c290e4e-1d3b-bc6e-c6e6-28a0414b866e@redhat.com> <20190815164821.GE7415@linux.fritz.box> From: John Snow Openpgp: preference=signencrypt Autocrypt: addr=jsnow@redhat.com; prefer-encrypt=mutual; keydata= mQINBFTKefwBEAChvwqYC6saTzawbih87LqBYq0d5A8jXYXaiFMV/EvMSDqqY4EY6whXliNO IYzhgrPEe7ZmPxbCSe4iMykjhwMh5byIHDoPGDU+FsQty2KXuoxto+ZdrP9gymAgmyqdk3aV vzzmCa3cOppcqKvA0Kqr10UeX/z4OMVV390V+DVWUvzXpda45/Sxup57pk+hyY52wxxjIqef 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[Qemu-devel] [PATCH 2/2] qapi: deprecate implicit filters X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: qemu-devel@nongnu.org, Vladimir Sementsov-Ogievskiy , qemu-block@nongnu.org, libvir-list@redhat.com, armbru@redhat.com, mreitz@redhat.com, den@openvz.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On 8/15/19 12:48 PM, Kevin Wolf wrote: > Am 15.08.2019 um 18:07 hat John Snow geschrieben: >> On 8/15/19 6:49 AM, Kevin Wolf wrote: >>> Am 14.08.2019 um 21:27 hat John Snow geschrieben: >>>> >>>> This might be OK to do right away, though. >>>> >>>> I asked Markus this not too long ago; do we want to amend the QAPI >>>> schema specification to allow commands to return with "Warning" strings, >>>> or "Deprecated" stings to allow in-band deprecation notices for cases >>>> like these? >>>> >>>> example: >>>> >>>> { "return": {}, >>>> "deprecated": True, >>>> "warning": "Omitting filter-node-name parameter is deprecated, it will >>>> be required in the future" >>>> } >>>> >>>> There's no "error" key, so this should be recognized as success by >>>> compatible clients, but they'll definitely see the extra information. >>>> >>>> Part of my motivation is to facilitate a more aggressive deprecation of >>>> legacy features by ensuring that we are able to rigorously notify users >>>> through any means that they need to adjust their scripts. >>> >>> Who would read this, though? In the best case it ends up deep in a >>> libvirt log that nobody will look at because there was no error. In the >>> more common case, the debug level is configured so that QMP traffic >>> isn't even logged. >>> >>> Kevin >>> >> >> I believe you are right, but I also can't shake the feeling that this >> attitude ensures that we'll never find a way to expose this information >> to the end-user. Is this not too defeatist? > > I think the discussed approach that seemed most likely to me to succeed > was adding a command line option that makes QEMU just crash if you use a > deprecated feature, and enable that in libvirt test cases (or possibly > even any non-release builds, though maybe it's a bit harsh there). > >> I think deprecation notices in the QMP stream has two benefits: >> >> 1) Any direct usages via qmp-shell or manual JSON connection are likely >> to see this message in development or testing. I feel the usage of QEMU >> directly is more likely to increase with time as other stacks seek to >> work around libvirt. >> >> [Whether or not they should is another question, but I believe the >> current reality to be that people are trying to.] > > I don't know about other people, but as a human user, I don't care about > deprecation notices. As long as something works, I use it, and once I > get an error message back, I'll use something else. > > If I manually enter drive_mirror and get a warning back, that doesn't > tell me that libvirt still does the same thing and needs to be fixed. It > just tells me that in the future I might need to change the commands > that I use manually. > That the message we return needs to be *useful* doesn't sound like a count against it. > I guess this would still prevent adding new libvirt features that build > on deprecated QEMU features because some manual testing will be involved > there. But was this ever a problem? > No, because until recently we didn't deprecate anything. >> 2) Programmatic deprecation notices can't be presented to a user at all >> if we don't send them; at least this way it becomes libvirt's problem >> over what to do with them. Perhaps even just in testing and regression >> suites libvirt can assert that it sees no deprecation warnings (or >> whitelist certain ones it knows about.) >> >> In the case of libvirt, it's not even necessarily about making sure the >> end user sees it, because it isn't even necessarily the user's fault -- >> it's libvirt's. This is a sure-fire programmatic way to communicate >> compatibility changes to libvirt. > > If libvirt uses this to make test cases fail, it could work. > Yeah, I think there's solid use there. I'll continue along in Markus's thread. > Kevin >