[libvirt] [PATCH v2] libxl: define a per-domain logger.

[Jim Fehlig]

On 01/06/2017 01:04 AM, Cedric Bosdonnat wrote:
> On Thu, 2017-01-05 at 15:45 -0700, Jim Fehlig wrote:
>> Cédric Bosdonnat wrote:
>>> libxl doesn't provide a way to write one log for each domain. Thus
>>> we need to demux the messages. If our logger doesn't know to which
>>> domain to attribute a message, then it will write it to the default
>>> log file.
>>>
>>> Starting with Xen 4.9 (commit f9858025 and following), libxl will
>>> write the domain ID in an easy to grab manner. The logger introduced
>>> by this commit will use it to demux the libxl log messages.
>>
>> One thing I noticed when testing this on a Xen installation prior to that commit
>> is log files are created that will never be written to. E.g. after starting
>> libvirtd and one domain
>>
>> # ll /var/log/libvirt/libxl/
>> -rw-r--r-- 1 root root     0 Jan  5 15:48 Domain-0.log
>> -rw-r--r-- 1 root root 17512 Jan  5 15:49 libxl-driver.log
>> -rw-r--r-- 1 root root     0 Jan  5 15:49 sles12sp2-hvm.log
>>
>> IMO these empty, never-to-be-written-to log files might be a bit confusing to
>> users. AFAIK there is no way to detect up front that the underlying Xen supports
>> this capability right?
>
> No there is no way to know it since there is no public API change
> in libxl. The only thing we can do is delaying the creation of the file
> to the first message write.

I think that is a wise thing to do, otherwise I envision bug reports such as "my 
domain log files are 0 bytes" :-).

Regards,
Jim