Message-Id: <20250507110444.963779-1-bhupesh@igalia.com>
Date: Wed,  7 May 2025 16:34:41 +0530
From: Bhupesh <bhupesh@...lia.com>
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Subject: [PATCH v3 0/3] Add support for long task name

Changes since v2:
================
- v2 can be seen here: https://lore.kernel.org/lkml/20250331121820.455916-1-bhupesh@igalia.com/
- As suggested by Yafang and Kees, picked Linus' suggested approach for
  this version (see: <https://lore.kernel.org/all/CAHk-=wjAmmHUg6vho1KjzQi2=psR30+CogFd4aXrThr2gsiS4g@mail.gmail.com/>).
- Dropped kthreads patch from this version. It would be sent out
  separately, if we have a consensus on this approach.

Changes since v1:
================
- v1 can be seen here: https://lore.kernel.org/lkml/20250314052715.610377-1-bhupesh@igalia.com/
- As suggested by Kees, added [PATCH 3/3] to have a consistent
  'full_name' entry inside 'task_struct' which both tasks and
  kthreads can use.
- Fixed the commit message to indicate that the existing ABI
  '/proc/$pid/task/$tid/comm' remains untouched and a parallel
  '/proc/$pid/task/$tid/full_name' ABI for new (interested) users.

While working with user-space debugging tools which work especially
on linux gaming platforms, I found that the task name is truncated due
to the limitation of TASK_COMM_LEN.

Now, during debug tracing, seeing truncated names is not very useful,
especially on gaming platforms where the number of tasks running can
be very high.

This patch does not touch 'TASK_COMM_LEN' at all, i.e.
'TASK_COMM_LEN' and the 16-byte design remains untouched.

In this version, as Linus suggested, we can add the
following union inside 'task_struct':
       union {
               char    comm[TASK_COMM_LEN];
               char    real_comm[REAL_TASK_COMM_LEN];
       };

and then modify '__set_task_comm()' to pass 'tsk->real_comm'
to the existing users.

So, eventually:
- users who want the existing 'TASK_COMM_LEN' behavior will get it
  (existing ABIs would continue to work),
- users who just print out 'tsk->comm' as a string will get the longer
  new "real comm",
- users who do 'sizeof(->comm)' will continue to get the old value
  because of the union.

After this change, gdb is able to show full name of the task, using a
simple app which generates threads with long names [see 1]:
  # gdb ./threadnames -ex "run info thread" -ex "detach" -ex "quit" > log
  # cat log

  NameThatIsTooLongForComm[4662]

[1]. https://github.com/lostgoat/tasknames

Bhupesh (3):
  exec: Remove obsolete comments
  treewide: Switch memcpy() users of 'task->comm' to a more safer
    implementation
  exec: Add support for 64 byte 'tsk->real_comm'

 fs/exec.c                      |  6 +++---
 include/linux/coredump.h       |  3 ++-
 include/linux/sched.h          | 14 ++++++++------
 include/trace/events/block.h   |  5 +++++
 include/trace/events/oom.h     |  1 +
 include/trace/events/osnoise.h |  1 +
 include/trace/events/sched.h   | 13 +++++++++++++
 include/trace/events/signal.h  |  1 +
 include/trace/events/task.h    |  2 ++
 9 files changed, 36 insertions(+), 10 deletions(-)

-- 
2.38.1

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