Kernel tracing from inside a Docker container

[Dirk Eibach via lttng-dev <lttng-dev@lists.lttng.org>]

Hi,

sorry, Outlook is messing up my plaintext mails, so I am switching to
my gmail account.

> lttng-modules exposes its control ABI through the virtual file /proc/lttng.
>
> Does you container have access to that file ?

The container is running in privileged mode.
root@9348eb19e6f4:/# ls -l /proc/lttng
-rw------- 1 root root 0 Nov  6 16:05 /proc/lttng

> Note that if you give access to that file within the container, then the container
> can observe detailed information about kernel internals (including related to
> other containers).

This is a development-only system, so the security implications are acceptable.

I have observed one more thing. When I start the session daemon with
the -vvv option I get:
root@9348eb19e6f4:/# lttng list --kernel
DBG1 - 07:31:23.811796947 [Client management]: Wait for client
response (in thread_manage_clients() at client.c:2576)
DBG1 - 07:31:23.811867247 [Client management]: Receiving data from
client ... (in thread_manage_clients() at client.c:2604)
DBG1 - 07:31:23.811945247 [Client management]: Processing client
command 'LTTNG_LIST_TRACEPOINTS' (14) (in process_client_msg() at
client.c:1016)
Error: Failed to load kmod library resources
Warning: No kernel tracer available
DBG1 - 07:31:23.812076447 [Client management]: Missing llm header,
creating one. (in process_client_msg() at client.c:2381)
DBG1 - 07:31:23.812085547 [Client management]: Sending response (size:
24, retcode: Kernel tracer not available (33)) (in
thread_manage_clients() at client.c:2683)
DBG1 - 07:31:23.812156547 [Client management]: Accepting client
command ... (in thread_manage_clients() at client.c:2534)
Error: Unable to list kernel events: Kernel tracer not available

Regards
Dirk