linux-kernel - Re: [oss-security] [patch] proc.5: tell how to parse /proc/*/stat correctly

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Date:   Wed, 28 Dec 2022 20:57:04 +0100
From:   Alejandro Colomar <alx.manpages@...il.com>
To:     Shawn Webb <shawn.webb@...denedbsd.org>,
        oss-security@...ts.openwall.com,
        John Helmert III <ajak@...too.org>,
        Demi Marie Obenour <demi@...isiblethingslab.com>,
        Jan Engelhardt <jengelh@...i.de>,
        "Lyndon Nerenberg (VE7TFX/VE6BBM)" <lyndon@...hanc.ca>
Cc:     Michael Kerrisk <mtk.manpages@...il.com>,
        linux-kernel@...r.kernel.org, linux-man@...r.kernel.org
Subject: Re: [oss-security] [patch] proc.5: tell how to parse /proc/*/stat
 correctly

Hi all,

On 12/28/22 20:24, Shawn Webb wrote:
> On Wed, Dec 28, 2022 at 01:02:35PM -0500, Demi Marie Obenour wrote:
>> On Wed, Dec 28, 2022 at 12:25:17PM -0500, Shawn Webb wrote:
>>> On Wed, Dec 28, 2022 at 11:47:25AM -0500, Demi Marie Obenour wrote:
>>>> On Wed, Dec 28, 2022 at 10:24:58AM -0500, Shawn Webb wrote:
>>>>> On Tue, Dec 27, 2022 at 04:44:49PM -0800, Lyndon Nerenberg (VE7TFX/VE6BBM) wrote:
>>>>>> Dominique Martinet writes:
>>>>>>
>>>>>>> But, really, I just don't see how this can practically be said to be parsable...
>>>>>>
>>>>>> In its current form it never will be.  The solution is to place
>>>>>> this variable-length field last.  Then you can "cut -d ' ' -f 51-"
>>>>>> to get the command+args part (assuming I counted all those fields
>>>>>> correctly ...)
>>>>>>
>>>>>> Of course, this breaks backwards compatability.
>>>>>
>>>>> It would also break forwards compatibility in the case new fields
>>>>> needed to be added.
>>>>>
>>>>> The only solution would be a libxo-style feature wherein a
>>>>> machine-parseable format is exposed by virtue of a file extension.
>>>>>
>>>>> Examples:
>>>>>
>>>>> 1. /proc/pid/stats.json
>>>>> 2. /proc/pid/stats.xml
>>>>> 3. /proc/pid/stats.yaml_shouldnt_be_a_thing
>>>>
>>>> A binary format would be even better.  No risk of ambiguity.
>>>
>>> I think the argument I'm trying to make is to be flexible in
>>> implementation, allowing for future needs and wants--that is "future
>>> proofing".
>>
>> Linux should not have an XML, JSON, or YAML serializer.  Linux already
>> does way too much; let’s not add one more thing to the list.
> 
> Somewhat agreed. I think formats like JSON provide a good balance
> between machine parseable and human readable.
> a
> As I described earlier, though, when it comes to concepts like procfs
> and sysfs, I have a bias towards abandoning them in favor of sysctl.
> If sysctl nodes were to be used, no new serialization formats would
> need to be implemented--and developers would also use a safter method
> of system and process inspection and manipulation.
> 

Just a comment as someone who is reading without much understanding of the 
contents of /prod/pid/stat:

If organization of the data in the file is a problem, and the format starts to 
matter, maybe it's a hint that there are too many different contents, and could 
be split into different files, each one with its own formatting rules.  I'll 
suggest that maybe a set of files, maybe contained in a common directory 
stats.d, is what you're looking for?

Binary format is not of my preference, since most user-space tools work with the 
standard interface, that is, text.

Cheers,

Alex

-- 
<http://www.alejandro-colomar.es/>

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