On Wed, Jul 11, 2018 at 01:40:31PM +0200, Bjoern Walk wrote:
Jiri Denemark <jdene...@redhat.com> [2018-07-11, 01:17PM +0200]:On Wed, Jul 11, 2018 at 12:49:13 +0200, Bjoern Walk wrote: > This patch series introduces the ability to save additional information > for the domain state and exposes this information in virsh domstate. > > For example in the case of QEMU guest panic events, we can provide additional > information like the crash reason or register state of the domain. This > information usually gets logged in the domain log but for debugging it is > useful to have it accessible from the client. Therefore, let's introduce a new > public API function, virDomainGetStateParams, an extensible version of > virDomainGetState, which returns the complete state of the domain, including > newly introduced additional information. > > Let's also extend virsh domstate and introduce a new parameter --info to show > the domain state, reason and additional information when available. > > virsh # domstate --info guest-1 > crashed (panicked: disabled-wait core='1' psw-mask='0x000000000010f146' \ > psw-addr='0x0002000180000000')I was thinking you introduced a new API with typed parameters so that you can return each part of the info string as a separate parameter with a defined semantics. But I was wrong, you're just adding a new opaque string with more details about the reason. In that case typed parameters don't actually bring any additional value, they just complicate the usage of the API. The following prototype would be much betterThe extensibility for this new API was more regarding for future additions of any state related information. Since libvirt does not have a deprecation model for APIs, whenever we would want to return additional information for the state (like in this case) a new API function has to be created.int virDomainGetState...(virDomainPtr domain, int *state, int *reason, char **info, unsigned int flags) On the other hand, is an opaque string really a good idea? It makes the additional info usable only for being shown to the user rather than being processed by an upper management layer. That's probably fine for crashed state, but perhaps other states would want to return something that is supposed to be processed. Maybe I'm just overthinking this, but I'd like to avoid having to add yet another API later. So the API could have the following prototypeSure, if machine readability is a goal this approach makes certainly more sense. On the other hand, the same information can be queried by a qemu-monitor-command call and retrieved in JSON format. This information here is aimed at human interaction, similar to the log output. It is also unclear which platforms/hypervisors would provide what information and mapping all of them to a virTypedParameter entry could result in a rather large list. Certainly no arguments against your objection, and if the overall concensus is that this is something we want, I can definitely rework the API.
I'm not very particularly opinionated on this, but I think APIs should be machine-readable and CLI tools can convert that to human-readable format. You'll never know when a program will like to access that and having to tell anyone in the future that they need to parse a string is ugly IMHO. Also from the monitor you can get that information only if there is any QEMU running. I presume the state you are returning is saved somewhere along with the reason so that it can be provided later.
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