Re: [Xen-devel] tools/libacpi printf output to logging instead of console/stdout ?

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 08/03/18 19:23, Sander Eikelenboom wrote:
> On 08/03/18 10:09, Jan Beulich wrote:
>>>>> On 07.03.18 at 21:52, <linux@xxxxxxxxxxxxxx> wrote:
>>> When starting a guest with the 'xl create' command (non-verbose) i get
>>> this extra output on PVH guest types only:
>>>
>>> S3 disabled
>>> S4 disabled
>>> CONV disabled
>>>
>>>
>>> It seems libacpi/* only contains normal printf's, so for the other guest
>>> types i probably just never triggered one of them.
>>>
>>> Shouldn't these printf's go to logging instead of console/stdout ?
>> I think it's the responsibility of the executable linking to that library
>> to suitably set up / redirect stdout. There not being anything like
>> "stdlog", I'm also not sure where you would think libacpi should
>> send them (if it was to control this itself) - surely not stderr.
> The extra output seems only informational, not even a warning, so stderr
> seems wrong indeed.
>
> With my novice C skills it seems that:
> The difference between HVM and PVH is that 
> in the HVM case the code of libacpi is linked to and gets run by
> the hvmloader binary, which libxl captures all the output from
> and only prints on verbose invocation of the xl tool and/or the xen log
> (on debug builds).
>
> In the PVH case the acpi tables are generated by libxl it
> self (libxl_x86_acpi.c: libxl__dom_load_acpi()), which is linked to libacpi 
> directly, 
> hence the output can't be captured separately since it is not a separate 
> binary.
>
> Would probably be hard to align the logging with those 2 different way of 
> using libacpi ?

libxl has no interaction with hvmloader's logging, as hvmloader runs in
guest context.

I see no purpose for those three printks.  I'd drop them completely,
rather than worrying about how to plumb together the logging for the
multiple scenarios.

~Andrew

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