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Tue, 07 Apr 2026 08:14:36 -0700 (PDT) MIME-Version: 1.0 References: <4a6fd540-da30-419e-b311-1fdf17306cef@efficios.com> In-Reply-To: <4a6fd540-da30-419e-b311-1fdf17306cef@efficios.com> Date: Tue, 7 Apr 2026 11:14:25 -0400 X-Gm-Features: AQROBzA4ylJ_SkChZ8B6K8HjPHXFO00mbh0HnvTeJC5Q3TQ3njizCdhlnw3NgHA Message-ID: Subject: Re: Question about LTTng Kernel Probe Tracking To: Kienan Stewart Content-Type: multipart/alternative; boundary="000000000000c289fc064ee03d7e" X-Mailman-Approved-At: Tue, 07 Apr 2026 15:23:40 -0400 X-BeenThere: lttng-dev@lists.lttng.org X-Mailman-Version: 2.1.39 Precedence: list List-Id: LTTng development list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Amir Najafi Zadeh via lttng-dev Reply-To: Amir Najafi Zadeh Errors-To: lttng-dev-bounces@lists.lttng.org Sender: "lttng-dev" --000000000000c289fc064ee03d7e Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable Added LTTng dev to BCC to avoid spamming. Hi Kienan. Thanks for your response. I tried specifying the session name, but nothing changed. Here is the output I get after adding the tracker: Added 1002 to the group ID tracker inclusion set I don=E2=80=99t think the session name is the issue, because I also specifi= ed the session name when starting tracking. This is the session state after creating it: $ sudo lttng list lttng-gid-test Recording session lttng-gid-test: [active] Trace output: /tmp/lttng/lttng-gid-test =3D=3D=3D Domain: Linux kernel =3D=3D=3D Tracked process attributes Process IDs: none Virtual process IDs: none User IDs: none Virtual user IDs: none Group IDs: 1002 Virtual group IDs: none And these are the logs I get: [11:01:51.222277079] (+0.000004846) dhcp15 ext4_get_inode_loc: { cpu_id =3D 3 }, { pid =3D 403653, tid =3D 403660, procname =3D "lttng-consumerd", gid =3D 0, uid =3D 0, vpid =3D 403653, vuid =3D 0, vgid = =3D 0 }, { ip =3D 0xFFFFFFFFAC804940 } ... There are many logs like this from systemd, kworker, and processes belonging to other groups. Note that the GID 1002 that I want to trace currently has no active subjects. Do you suggest switching to the recent version of LTTng (current version 2.13.11)? Best, Amir On Tue, Apr 7, 2026 at 10:57=E2=80=AFAM Kienan Stewart wrote: > Hi Amir, > > On 2026-04-04 21:02, Amir Najafi Zadeh via lttng-dev wrote: > > Hello all, > > > > I hope you are doing well. > > > > I have a quick question about LTTng tracking when using kernel probes. = I > > mainly use LTTng to trace file system functions in the Linux kernel, an= d > > for that I use the LTTng kernel probe feature, which works very well. > > However, when I tried filtering logs for a specific group ID, I noticed > > that filters are not supported for kernel probes. > > > > Then I attempted to use the tracking feature to trace only a specific > > GID, but this also did not work. From what I see in my logs, it appears > > that for kernel probes all events are captured and recorded, regardless > > of the tracking options. > > > > I wanted to know if this is a known limitation, and whether there is an= y > > in-progress work or reason why this is not currently supported. > > > > I just tried on the master branch (since I had easy access to it), and > wasn't able to reproduce a situation where I added the gid tracking and > had results for a different gid in lttng view. > > > For reference, here is my code. I am using LTTng 2.13.11 with kernel > > 6.8.0-101-generic: > > > > ``` #!/bin/sh > > SESSION_NAME=3D"lttng-gid-test" > > OUTPUT_DIR=3D"/tmp/lttng/${SESSION_NAME}" > > GROUP_ID=3D1002 > > > > # create the lttng session > > lttng create "$SESSION_NAME" -o "$OUTPUT_DIR" > > > > # create the lttng ring buffer channel > > lttng enable-channel --session=3D"$SESSION_NAME" --kernel channel0 \ > > --subbuf-size=3D16M \ > > --num-subbuf=3D2 > > > > # add pid, tid, proc, and gid for tracing collection > > lttng add-context --session=3D"$SESSION_NAME" --channel=3Dchannel0 --ke= rnel > > --type pid > > lttng add-context --session=3D"$SESSION_NAME" --channel=3Dchannel0 --ke= rnel > > --type gid > > > > # enable the target probe > > lttng enable-event --session=3D"$SESSION_NAME" --channel=3Dchannel0 --k= ernel > > --probe=3Dext4_get_inode_loc ext4_get_inode_loc > > > > # disable all tracks # NOTE: untracking doesn't make a difference > > # lttng untrack --session=3D"$SESSION_NAME" --kernel --all --gid > > # lttng untrack --session=3D"$SESSION_NAME" --kernel --all --pid > > # lttng untrack --session=3D"$SESSION_NAME" --kernel --all --vpid > > # lttng untrack --session=3D"$SESSION_NAME" --kernel --all --uid > > # lttng untrack --session=3D"$SESSION_NAME" --kernel --all --vuid > > # lttng untrack --session=3D"$SESSION_NAME" --kernel --all --vgid > > # only enable gid 1002 track > > lttng track --kernel --gid=3D1002 > > > > Could you check the output of your script after "lttng track --kernel > --gid=3D1002"? > > The rest of your commands specify a session name, but this one does not. > I wonder if it's selecting a different default session that the one > you're expecting? > > > # start lttng lttng start $SESSION_NAME > > > > ``` > > > > Thank you for your time and guidance. > > > > Best regards, > > Amir > > > > -- > > *Amirhossein Najafizadeh* > > *PhD Student, Computer Science Department, Stony Brook University, N.Y. > > File systems and Storage Lab (FSL) > > > > * > > najafizadeh21@gmail.com > > https://amirhnajafiz.github.io/ > > --000000000000c289fc064ee03d7e Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

Added LTTng dev to BCC to avoid spamming.

Hi Kienan. Than= ks for your response. I tried specifying the session name, but nothing chan= ged.

Here is the output I get after add= ing the tracker:

Added 1002 to the gr=
oup ID tracker inclusion set

I= don=E2=80=99t think the session name is the issue, because I also specifie= d the session name when starting tracking. This is the session state after = creating it:

$ sudo lttng list lttng-=
gid-test
Recording session lttng-gid-test: [active]
    Trace output: /tmp/lttng/lttng-gid-test

=3D=3D=3D Domain: Linux kernel =3D=3D=3D

Tracked process attributes
  Process IDs:          none
  Virtual process IDs:  none
  User IDs:             none
  Virtual user IDs:     none
  Group IDs:            1002
  Virtual group IDs:    none

A= nd these are the logs I get:

[1=
1:01:51.222277079] (+0.000004846) dhcp15 ext4_get_inode_loc: { cpu_i=
d =3D 3 }, { pid =3D 403653, tid =3D 403660, procname =3D "lttng-consu=
merd", gid =3D 0, uid =3D 0, vpid =3D 403653, vuid =3D 0, vgid =3D 0 }=
, { ip =3D 0xFFFFFFFFAC804940 }
...

There are many logs like this from systemd, kworker, and= processes belonging to other groups. Note that the GID 1002 that I want to= trace currently has no active subjects.

Do you suggest switching to= the recent version of LTTng (current version 2.13.11)?=C2=A0

Best,<= br>Amir


On Tue, Apr 7, 2026 at 10:57=E2=80=AFAM Ki= enan Stewart <kstewart@efficios= .com> wrote:
Hi Amir,

On 2026-04-04 21:02, Amir Najafi Zadeh via lttng-dev wrote:
> Hello all,
>
> I hope you are doing well.
>
> I have a quick question about LTTng tracking when using kernel probes.= I
> mainly use LTTng to trace file system functions in the Linux kernel, a= nd
> for that I use the LTTng kernel probe feature, which works very well. =
> However, when I tried filtering logs for a specific group ID, I notice= d
> that filters are not supported for kernel probes.
>
> Then I attempted to use the tracking feature to trace only a specific =
> GID, but this also did not work. From what I see in my logs, it appear= s
> that for kernel probes all events are captured and recorded, regardles= s
> of the tracking options.
>
> I wanted to know if this is a known limitation, and whether there is a= ny
> in-progress work or reason why this is not currently supported.
>

I just tried on the master branch (since I had easy access to it), and
wasn't able to reproduce a situation where I added the gid tracking and=
had results for a different gid in lttng view.

> For reference, here is my code. I am using LTTng 2.13.11 with kernel <= br> > 6.8.0-101-generic:
>
> ``` #!/bin/sh
> SESSION_NAME=3D"lttng-gid-test"
> OUTPUT_DIR=3D"/tmp/lttng/${SESSION_NAME}"
> GROUP_ID=3D1002
>
> # create the lttng session
> lttng create "$SESSION_NAME" -o "$OUTPUT_DIR"
>
> # create the lttng ring buffer channel
> lttng enable-channel --session=3D"$SESSION_NAME" --kernel ch= annel0 \
> --subbuf-size=3D16M \
> --num-subbuf=3D2
>
> # add pid, tid, proc, and gid for tracing collection
> lttng add-context --session=3D"$SESSION_NAME" --channel=3Dch= annel0 --kernel
> --type pid
> lttng add-context --session=3D"$SESSION_NAME" --channel=3Dch= annel0 --kernel
> --type gid
>
> # enable the target probe
> lttng enable-event --session=3D"$SESSION_NAME" --channel=3Dc= hannel0 --kernel
> --probe=3Dext4_get_inode_loc ext4_get_inode_loc
>
> # disable all tracks # NOTE: untracking doesn't make a difference<= br> > # lttng untrack --session=3D"$SESSION_NAME" --kernel --all -= -gid
> # lttng untrack --session=3D"$SESSION_NAME" --kernel --all -= -pid
> # lttng untrack --session=3D"$SESSION_NAME" --kernel --all -= -vpid
> # lttng untrack --session=3D"$SESSION_NAME" --kernel --all -= -uid
> # lttng untrack --session=3D"$SESSION_NAME" --kernel --all -= -vuid
> # lttng untrack --session=3D"$SESSION_NAME" --kernel --all -= -vgid
> # only enable gid 1002 track
> lttng track --kernel --gid=3D1002
>

Could you check the output of your script after "lttng track --kernel =
--gid=3D1002"?

The rest of your commands specify a session name, but this one does not. I wonder if=C2=A0 it's selecting a different default session that the o= ne
you're expecting?

> # start lttng lttng start $SESSION_NAME
>
> ```
>
> Thank you for your time and guidance.
>
> Best regards,
> Amir
>
> --
> *Amirhossein Najafizadeh*
> *PhD Student, Computer Science Department, Stony Brook University, N.Y= .
> File systems and Storage Lab (FSL)
>
> *
> najafizad= eh21@gmail.com <mailto:najafizadeh21@gmail.com>
> https://amirhnajafiz.github.io/ <https://amirhnaja= fiz.github.io/>

--000000000000c289fc064ee03d7e--