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Sat, 04 Apr 2026 18:02:21 -0700 (PDT) MIME-Version: 1.0 Date: Sat, 4 Apr 2026 21:02:11 -0400 X-Gm-Features: AQROBzBwgePvh3VlE1LBJ6FiSsMzuHBrJu37U6jMlpBM0kBpdMjn2cxNyHlqMGk Message-ID: Subject: Question about LTTng Kernel Probe Tracking To: lttng-dev@lists.lttng.org Content-Type: multipart/alternative; boundary="0000000000003dca8e064eac1a48" 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" --0000000000003dca8e064eac1a48 Content-Type: text/plain; charset="UTF-8" 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, and 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 any in-progress work or reason why this is not currently supported. For reference, here is my code. I am using LTTng 2.13.11 with kernel 6.8.0-101-generic: ``` #!/bin/sh SESSION_NAME="lttng-gid-test" OUTPUT_DIR="/tmp/lttng/${SESSION_NAME}" GROUP_ID=1002 # create the lttng session lttng create "$SESSION_NAME" -o "$OUTPUT_DIR" # create the lttng ring buffer channel lttng enable-channel --session="$SESSION_NAME" --kernel channel0 \ --subbuf-size=16M \ --num-subbuf=2 # add pid, tid, proc, and gid for tracing collection lttng add-context --session="$SESSION_NAME" --channel=channel0 --kernel --type pid lttng add-context --session="$SESSION_NAME" --channel=channel0 --kernel --type gid # enable the target probe lttng enable-event --session="$SESSION_NAME" --channel=channel0 --kernel --probe=ext4_get_inode_loc ext4_get_inode_loc # disable all tracks # NOTE: untracking doesn't make a difference # lttng untrack --session="$SESSION_NAME" --kernel --all --gid # lttng untrack --session="$SESSION_NAME" --kernel --all --pid # lttng untrack --session="$SESSION_NAME" --kernel --all --vpid # lttng untrack --session="$SESSION_NAME" --kernel --all --uid # lttng untrack --session="$SESSION_NAME" --kernel --all --vuid # lttng untrack --session="$SESSION_NAME" --kernel --all --vgid # only enable gid 1002 track lttng track --kernel --gid=1002 # 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/ --0000000000003dca8e064eac1a48 Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable

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, and f= or that I use the LTTng kernel probe feature, which works very well. Howeve= r, when I tried filtering logs for a specific group ID, I noticed that filt= ers are not supported for kernel probes.

Then I attempted to use the tracking feature to trace only a specific GI= D, 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 t= racking options.

I wanted to know if this is a known limitation, and whether there is any= in-progress work or reason why this is not currently supported.

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&quo=
t;/tmp/lttng/${SESSION_NAME}"
GROUP_ID=3D1002

# create the l=
ttng session
lttng create "$SESSION_NAME" -o "$OUTPUT_DIR=
"

# create the lttng ring buffer channel
lttng enable-channe=
l --session=3D"$SESSION_NAME" --kernel channel0 \
  --subbuf-s=
ize=3D16M \
  --num-subbuf=3D2

# add pid, tid, proc, and gid for =
tracing collection
lttng add-context --session=3D"$SESSION_NAME&quo=
t; --channel=3Dchannel0 --kernel --type pid
lttng add-context --session=
=3D"$SESSION_NAME" --channel=3Dchannel0 --kernel --type gid
# enable the target probe
lttng enable-event --session=3D"$SESSIO=
N_NAME" --channel=3Dchannel0 --kernel --probe=3Dext4_get_inode_loc ext=
4_get_inode_loc

# disable all tracks
# NOTE: untracking doesn't make a difference
# lttng untrack --sessi=
on=3D"$SESSION_NAME" --kernel --all --gid
# lttng untrack --se=
ssion=3D"$SESSION_NAME" --kernel --all --pid
# lttng untrack -=
-session=3D"$SESSION_NAME" --kernel --all --vpid
# lttng untra=
ck --session=3D"$SESSION_NAME" --kernel --all --uid
# lttng un=
track --session=3D"$SESSION_NAME" --kernel --all --vuid
# lttn=
g untrack --session=3D"$SESSION_NAME" --kernel --all --vgid
# only enable gid 1002 track
lttng track --kernel --gid=3D1002

=
# start lttng
lttng start $SESSION_NAME

```

Thank you for your time and guidance.

Best regards,
Amir

--=
Amirhossein Najafizadeh
PhD Student, Computer Science Department, Stony Broo= k University, N.Y.
File systems and Storage Lab (FSL)

=
--0000000000003dca8e064eac1a48--