Error messages are issued when enabling all events in a new channel
lttng enable-event --all -k command assigns the as-yet-unassigned kernel tracepoints and syscalls. This is a quiet process within any given channel. For example, if you enable a handful of
sched_* tracepoints to a channel, and then issue
lttng enable-event --all -k for that same channel, it will receive the syscalls and all the remaining kernel events, with no error messages.
However, if you switch channels:
# lttng enable-events -k --tracepoint --all -c channel_one # lttng enable-events -k --all -c channel_two
You will get a long series of identical errors, one for each current kernel tracepoint. The session correctly ends up enabling just the syscalls in
channel_two, so the error messages are not pertinent.
PERROR [19839/19940]: create event ioctl: Invalid argument (in kernel_create_event() at kernel.c:205)
The converse also occurs:
# lttng enable-events -k --syscall --all -c channel_one # lttng enable-events -k --all -c channel_two
You will get one escaping error message (the same one), when lttng tries to assign the syscalls to the other channel. Also happens if the second command adds
--syscall, which is expected. The error message could be improved, though ("The syscall events are already assigned to another channel" instead of "Enable kernel event failed (channel x, session y)").
# lttng enable-events -k sched_switch -c channel_one # lttng enable-events -k --all -c channel_two
You will get one escaping error message (the same one), when lttng tries to assign
sched_switch to the other channel. Also happens if the second command adds
Using LTTng 2.3.0.
Updated by Daniel U. Thibault over 6 years ago
The following is most likely just another symptom of the same underlying problem, so I won't open a distinct bug report.
If, in a given channel, you enable syscalls and then enable all kernel tracepoints, you get no error or warning messages. But if you enable the tracepoints first, then the syscalls, you get a warning even though everything is OK:
$ lttng create syscalls_then_tracepoints Session syscalls_then_tracepoints created. Traces will be written in /home/daniel/lttng-traces/syscalls_then_tracepoints-20131028-151011 $ lttng enable-event -k -a --syscall All kernel system calls are enabled in channel channel0 $ lttng enable-event -k -a All kernel events are enabled in channel channel0 $ lttng create tracepoints_then_syscalls Session tracepoints_then_syscalls created. Traces will be written in /home/daniel/lttng-traces/tracepoints_then_syscalls-20131028-151937 $ lttng enable-event -k -a All kernel events are enabled in channel channel0 $ lttng enable-event -k -a --syscall Warning: Kernel events already enabled (channel channel0, session tracepoints_then_syscalls)
Updated by David Goulet about 6 years ago
- Status changed from Confirmed to Feedback
This is a recurrent issue we've been having with already existing event where the lttng modules returns EINVAL but should return EEXIST instead. If I remember correctly, there is unfortunately no way to have the kernel return EEXIST in the current implementation.
Mathieu can you confirm that? If yes, we'll have to live with that annoying UI/UX issue. :S