LTTng » LTTng-tools

The 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 --tracepoint.

Using LTTng 2.3.0.