lttng snapshot record can erroneously claim a successful snapshot
If a session is created with just the
no-output option, the
snapshot commands are possible, but they fail while giving the appearance of success:
$ sudo -H lttng create nooutmm --no-output Session nooutmm created. $ sudo -H lttng enable-channel channel0 --discard --output mmap -k Kernel channel channel0 enmabled for session nooutmm $ sudo -H lttng enable-event -k -a -c channel0 All kernel events are enabled in channel channel0 $ sudo -H lttng start Tracing started for session nooutmm $ sudo -H lttng snapshot record Snapshot recorded successfully for session nooutmm $ sudo -H lttng stop Waiting for data availability Tracing stopped for session nooutmm $ sudo -H lttng destroy -a Session nooutmm destroyed
Despite lttng reporting
'Snapshot recorded successfully for session nooutmm', no such capture occurs.
lttng snapshot record command also fails if the kernel events are using the
splice output mode (it is the default, after all), and again claims everything went okay. The log is essentially identical to that given above.