On 4/1/19 1:14 PM, Bjoern Walk wrote:
Michal Privoznik <mprivozn@xxxxxxxxxx> [2019-04-01, 10:49AM +0200]:
On 4/1/19 10:17 AM, Bjoern Walk wrote:
I intent to have the new API function superseed the existing one, so I
actually want to call virDomainGetStateParams() unconditionally and only
fall back to virshDomainState() when the new API is not there (so that
hopefully at some distant point in the future, we could deprecate the
old stuff).
I understand that but consider the following scenario: a shell script that
calls 'virsh domstate $dom' every so often. If we switch to new API then
this will still fetch expected info for the client but also it will produce
an error message logged at the server side (if it is old and doesn't support
the new API).
That's the main reason I think we should use new API only if necessary, i.e.
if --info was requested. But if you still want to prefer the new API we
should do it the proper way. That is something among these lines:
if (virDomainGetStateParams() < 0) {
if (!last_error || last_error->code != VIR_ERR_NO_SUPPORT)
goto error;
/* fallback */
if (virshDomainState() < 0)
goto error;
}
Note that we have to check for the reason why vurDomainGetStateParams()
failed and fallback on old API if and only if the new API is not supported.
Which would still generate the server-side error message, right?
Yes, it would.
If this
is an issue, it's an issue and I will use your initial suggestion.
Otherwise, something like the above seems cleaner. I will have to think
about this.
Well, to be fair we use something like this. For instance when listing
domains/networks/... But there is a clear advantage of using 'new'
virConnectListAll*() over 'old' GetNumDomains() + ListDomains() +
GetDefinedDomains() + ListDefinedDomains() - they are atomic. But what
is the advantage of using the new API in case of plain 'virsh domstate'?
BTW: We don't really have notion of deprecating an API. We can merely
say 'don't use this, use that because reasons' in the docs. But we still
have to fix all APIs / maitain them.
This is the reason I am advocating for using new API only if neccessary.
Also, printing out some error message would be nice:
If the new API is not available, I wanted to just silently have the old
behaviour. The domain state and reason can always be retrieve (by means
of the old API) only additional information could be missing. I am not
sure if we should error out if this is the case.
I think we should. I mean, if I'd run 'virsh domstate --info' that means I
am expecting some extended info on domain state. If I don't get it, isn't
that a failure?
There can also be no additional information available, think different
domain states or other hypervisors, for which also silently no further
information is printed. Should we do something about this scenario too?
No. That is perfectly okay. The API succeeded, but there is no
additional info.
Michal
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