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

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.