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From:   Yafang Shao <laoar.shao@gmail.com>
Date:   Fri, 5 Nov 2021 14:34:58 +0800
Message-ID: <CALOAHbDtoBEr8TuuUEMAnw3aeOf=S10Lh_eBCS=5Ty+JHgdj0Q@mail.gmail.com>
Subject: Re: [PATCH v7 00/11] extend task comm from 16 to 24
To:     =?UTF-8?B?TWljaGHFgiBNaXJvc8WCYXc=?= <mirq-linux@rere.qmqm.pl>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Kees Cook <keescook@chromium.org>,
        Steven Rostedt <rostedt@goodmis.org>,
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        Petr Mladek <pmladek@suse.com>,
        Peter Zijlstra <peterz@infradead.org>,
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On Thu, Nov 4, 2021 at 9:37 AM Micha=C5=82 Miros=C5=82aw <mirq-linux@rere.q=
mqm.pl> wrote:
>
> On Mon, Nov 01, 2021 at 06:04:08AM +0000, Yafang Shao wrote:
> > There're many truncated kthreads in the kernel, which may make trouble
> > for the user, for example, the user can't get detailed device
> > information from the task comm.
> >
> > This patchset tries to improve this problem fundamentally by extending
> > the task comm size from 16 to 24, which is a very simple way.
> [...]
>
> Hi,
>
> I've tried something like this a few years back. My attempt got mostly
> lost in the mailing lists, but I'm still carrying the patches in my
> tree [1]. My target was userspace thread names, and it turned out more
> involved than I had time for.
>
> [1] https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3D2c3814268caf2b1fee=
6d1a0b61fd1730ce135d4a
>     and its parents
>

Hi Michal,

Thanks for the information.

I have looked through your patches.  It seems to contain six patches
now and can be divided into three parts per my understanding.

1. extend task comm len
This parts contains below 4 patches:
[prctl: prepare for bigger
TASK_COMM_LEN](https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3Dcfd99db9c=
f911bb4d106889aeba1dfe89b6527d0)
[bluetooth: prepare for bigger
TASK_COMM_LEN](https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3Dba2805f51=
96865b81cc6fc938ea53af2c7c2c892)
[taskstats: prepare for bigger
TASK_COMM_LEN](https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3D4d29bfedc=
57b36607915a0171f4864ec504908ca)
[mm: make TASK_COMM_LEN
configurable](https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3D362acc3558=
2445174589184c738c4d86ec7d174b)

What kind of userspace issues makes you extend the task comm length ?
Why not just use /proc/[pid]/cmdline ?

2.  A fix
Below patch:
[procfs: signal /proc/PID/comm write
truncation](https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3Dd72027388d4d=
95db5438a7a574e0a03ae4b5d6d7)

It seems this patch is incomplete ?   I don't know what it means to do.

3. A feature provided for pthread_getname_np
Below patch:
[procfs: lseek(/proc/PID/comm, 0,
SEEK_END)](https://rere.qmqm.pl/git/?p=3Dlinux;a=3Dcommit;h=3D2c3814268caf2=
b1fee6d1a0b61fd1730ce135d4a)

It seems this patch is useful. With this patch the userspace can
directly get the TASK_COMM_LEN through the API.

--=20
Thanks
Yafang