LTTng » LTTng-tools

Hi,

The problem is due to the lack of update of the python binding through time and the addition of extended attributes to the channel object.

commit cf0bcb51ea857687a353d2851e572dba6cc63cb0
Author: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Date:   Thu May 4 23:53:50 2017 -0400

    Expose monitor timer interval to lttngctl and client

    Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>

The relevant part in lttng_enable_channel:

if (!in_chan->attr.extended.ptr) {
        struct lttng_channel *channel;
        struct lttng_channel_extended *extended;

        channel = lttng_channel_create(&handle->domain);
        if (!channel) {
            return -LTTNG_ERR_NOMEM;
        }

        /*
         * Create a new channel in order to use default extended
         * attribute values.
         */
        extended = (struct lttng_channel_extended *)
                channel->attr.extended.ptr;
        memcpy(&lsm.u.channel.extended, extended, sizeof(*extended));
        lttng_channel_destroy(channel);

Notice the LTTNG_ERR_NOMEM. Using gdb we find that lttng_channel_create fail on the validation for the domain buffer type. Note that currently the buffer type is not exposed for the Domain object in the bindings and default to 0.

    case LTTNG_DOMAIN_KERNEL:
        if (domain->buf_type != LTTNG_BUFFER_GLOBAL) {
            goto error;
        }
        break;

The default value (0) is LTTNG_BUFFER_PER_PID which correctly lead to an error in lttng_create_channel.

We are not sure yet how to fix this mess. Will keep you updated.

Cheers

Hi Christophe,

Would you be able to build a 2.10 lttng-tools from source and test the attached patches?

When building from source you will need to enable the python bindings at configure time.

./configure --enable-python-bindings

You will also need to add the following for both your kernel and userspace Domain object.

domain_kernel.buf_type = BUFFER_GLOBAL
domain_ust.buf_type = BUFFER_PER_UID

Unless you want per-pid buffering, which is rarely the case.

Cheers

Hi,

The fix is part of lttng 2.10.7 stable release.

https://github.com/lttng/lttng-tools/commit/93fa2c9ff6b52c30173bee80445501ce8677fecc

The ubuntu latest stable ppa should do the trick [1].

The fix should land in the stable 2.10 ppa soon.

[1] https://launchpad.net/~lttng/+archive/ubuntu/ppa

Cheers