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

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" :-).