From: "Jan Beulich" <JBeulich@suse.com>
To: Wei Liu <wei.liu2@citrix.com>
Cc: xen-devel <xen-devel@lists.xenproject.org>,
Ian Jackson <Ian.Jackson@eu.citrix.com>,
Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Subject: Re: [PATCH v2 3/3] xl: new "loglvl" command
Date: Fri, 29 Apr 2016 01:20:57 -0600 [thread overview]
Message-ID: <5723277902000078000E7139@prv-mh.provo.novell.com> (raw)
In-Reply-To: <20160428153311.GB18194@citrix.com>
>>> On 28.04.16 at 17:33, <wei.liu2@citrix.com> wrote:
> On Wed, Mar 16, 2016 at 05:22:27AM -0600, Jan Beulich wrote:
>> >>> On 15.03.16 at 16:38, <Ian.Jackson@eu.citrix.com> wrote:
>> > Jan Beulich writes ("Re: [PATCH v2 3/3] xl: new "loglvl" command"):
>> >> Yes and no. If all of the sudden the hypervisor didn't have an "error"
>> >> log level anymore, what would you do? Mapping "error" to "warning"
>> >> wouldn't be right. Nor would mapping it to anything else. Correct
>> >> behavior in that case would simply be failure, and it wouldn't seem
>> >> too relevant to me at what layer that failure would get signaled.
>> >
>> > I think you are looking at this the wrong way.
>>
>> Quite possible, and all of what you write makes sense. Yet that
>> wasn't my intention here. I specifically put the string <-> number
>> mapping in xl, so it could be that (and only that, outside the
>> hypervisor itself) which gets changed if the hypervisor log levels
>> ever change. The tool could use version information or some
>> other detection mechanism to provide backwards compatibility
>> (and be independent of the precise hypervisor version it got
>> built in parallel with, if that's desired). And hence I specifically
>> made the interfaces dumb - raw numbers, with no meaning
>> assigned to their values.
>>
>> And then, with what you describe I assume the current hypervisor
>> side implementation wouldn't be suitable anymore anyway, as the
>> translation between the interface exposed log levels and the
>> internally used ones would need to happen in the sysctl handler.
>>
>> To me, all of this looks increasingly like over-engineering for a
>> very simple debugging aid (which is all the new command was
>> meant for). If you and Wei can settle on some alternative
>> implementation, I'm fine to accept that, but I don't think I'm
>> going to spend much more time on fiddling with any of the 3
>> patches. It's going to be sad though if even the serial console
>> based log level adjustment won't make it into 4.7, despite it
>> having got posted months ago (with this v2 just extending on
>> it).
>
> If this is just a debugging aid and not intending to be consumed by high
> level toolstack, maybe we can make a dedicated helper program? We
> already have a bunch of those. Should the need really arises we can
> then consider making it proper stable API / ABI.
That's an option, albeit a slightly awkward one. This new thing
really fits well with the debug-key and dmesg sub-commands,
which both are there just for debugging, too.
Jan
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next prev parent reply other threads:[~2016-04-29 7:20 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-04 16:38 [PATCH v2 0/3] allow runtime log level threshold adjustments Jan Beulich
2016-03-04 16:46 ` [PATCH v2 1/3] console: allow " Jan Beulich
2016-03-04 20:55 ` Konrad Rzeszutek Wilk
2016-03-07 10:44 ` Jan Beulich
2016-03-07 14:41 ` Konrad Rzeszutek Wilk
2016-03-07 15:19 ` Jan Beulich
2016-03-04 16:47 ` [PATCH v2 2/3] libxc: wrapper for log level sysctl Jan Beulich
2016-03-05 16:00 ` Dario Faggioli
2016-03-08 16:20 ` Wei Liu
2016-03-04 16:48 ` [PATCH v2 3/3] xl: new "loglvl" command Jan Beulich
2016-03-04 18:45 ` Dario Faggioli
2016-03-07 11:46 ` Jan Beulich
2016-03-07 18:07 ` Dario Faggioli
2016-03-08 8:08 ` Jan Beulich
2016-03-08 14:05 ` George Dunlap
2016-03-08 16:09 ` Wei Liu
2016-03-08 18:05 ` Dario Faggioli
2016-03-05 15:36 ` Dario Faggioli
2016-03-07 13:20 ` Fabio Fantoni
2016-03-07 13:26 ` Jan Beulich
2016-03-08 16:20 ` Wei Liu
2016-03-14 15:23 ` Jan Beulich
2016-03-14 15:36 ` Wei Liu
2016-03-14 15:49 ` Jan Beulich
2016-03-14 16:01 ` Wei Liu
2016-03-14 17:00 ` Jan Beulich
2016-03-14 17:07 ` Ian Jackson
2016-03-15 7:37 ` Jan Beulich
2016-03-15 13:58 ` Wei Liu
2016-03-15 14:07 ` Jan Beulich
2016-03-15 14:51 ` Wei Liu
2016-03-15 15:03 ` Jan Beulich
2016-03-15 15:38 ` Ian Jackson
2016-03-16 11:22 ` Jan Beulich
2016-04-28 15:33 ` Wei Liu
2016-04-29 7:20 ` Jan Beulich [this message]
2016-05-02 11:14 ` Wei Liu
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