OpenVMM Logging

Configuring OpenVMM logging messages to emit

To configure logging, use the OPENVMM_LOG environment variable. For example:

Enables debug events from all modules:

set OPENVMM_LOG=debug

Enables trace events from the mesh crate and info events from everything else:

set OPENVMM_LOG=info,mesh=trace

This is backed by the EnvFilter type; see the associated documentation for more details.

Configuring OpenHCL Trace Logging

If OpenHCL is used, it also supports an EnvFilter style trace logging options that can be configured using the OPENVMM_LOG= command line variable passed during OpenHCL startup with -c OPENVMM_LOG=. The -c argument in OpenVMM passes a string of command line arguments to OpenHCL initialization.

The environment variable configuration and style of OPENVMM_LOG for OpenHCL is the same for configuring tracing for OpenVMM.

OpenHCL tracing can also be configured and dumped at runtime with ohcldiag-dev. See: OpenHCL Diagnostics

To retrieve OpenHCL log output at runtime, an output console or file must attach to the OpenHCL logging COM port. By default, OpenHCL outputs to COM3.

To open a new terminal window with global OpenHCL debug level tracing enabled:

openvmm.exe -c "OPENVMM_LOG=debug" --com3 "term,name=VTL2 OpenHCL" [...]

Configure log levels of only a given module name:

openvmm.exe -c "OPENVMM_LOG=mesh=trace" --com3 "term,name=VTL2 OpenHCL" [...]

Multiple modules can be specified by separating them with a comma:

openvmm.exe -c "OPENVMM_LOG=mesh=trace,nvme_driver=trace" --com3 "term,name=VTL2 OpenHCL" [...]

Tip

For more configuration examples of serial ports and the OpenVMM CLI, see the Running OpenHCL Guide and CLI --help output.

Capturing the ETW traces on the host

On Windows, OpenVMM also logs to ETW, via the Microsoft.HvLite provider.

To capture the trace first need to start the session:

logman.exe start trace <SessionName> -ow -o FileName0.etl -p "{22bc55fe-2116-5adc-12fb-3fadfd7e360c}" 0xffffffffffffffff 0xff -nb 16 16 -bs 16 -mode 0x2 -ets

For OpenHCL traces, use {AA5DE534-D149-487A-9053-05972BA20A7C} as the provider GUID.

To flush:

logman.exe update <SessionName> -ets -fd

To stop:

logman.exe stop <SessionName> -ets

To decode as CSV:

tracerpt.exe <FileName0>.etl -y -of csv -o <FileName1>.csv -summary <FileName2>.summary