[PATCH] virprocess: Provide non-Linux stubs for virProcessGet{Stat, Sched}Info

[Ján Tomko]

On a Friday in 2022, Ani Sinha wrote:
>On Fri, 7 Jan 2022, Michal Prívozník wrote:
>> I don't think so. Just like we've discussed under one patch of yours, a
>> function should either report error in all cases or none. And in case of
>> virProcessGetSchedInfo() the linux version does report error
>
>I see your point but there is also a bug in that function - not all error
>paths report errors. For example, !proc and !lines cases. We need to fix
>that.
>

I don't see a !proc error path in virProcessGetSchedInfo.

The !lines case is inconsistent but thankfully it can only happen
if /proc/%d/sched is empty.

>hence the
>> non-linux variant should report an error too. And in case of
>> virProcessGetStatInfo() no error is reported for linux version thus
>> non-linux version shouldn't report an error.
>>
>
>No this is not my understanding from the discussion. What I understood is
>that the lowest level of functions should always report error when an
>error path is encountered.

Errors should be reported by the function that has the context to
provide a helpful error message. For some low-level helpers, we rely
on errno's and let the caller report a less-specific error - either
out of laziness because (like above) there would have to be a buggy
kernel, or because most of the code paths are syscalls which set errno.

Jano

>For example virFileReadAll() does this nicely.
>Currently there is no  error path in virProcessGetStatInfo() and it
>uncondiotionally returns 0. For non-linux variant, I think it would be
>correct to report an error.
>
>Now having done that, we should also fix the callers so that the callers
>are not overriding the narrower errors with broader ones.
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