Re: proc(5): /proc/[number]/cmdline explanation update

[Michael Kerrisk <mtk.manpages-gM/Ye1E23mwN+BqQ9rBEUg@public.gmane.org>]

Fernando Luis Vázquez Cao wrote:
> Hi Michael,
> 
> It seems the old description applies to all 2.0, 2.2, and 2.3 kernels up
> to and including 2.3.26. After that the behavior changed as explained in
> my patch.

Thanks.  Patch applied for man-pages-2.79.

Cheers,

Michael

> Fernando
> 
> On Mon, 2008-02-11 at 17:30 +0100, Michael Kerrisk wrote:
>> Fernando,
>>
>> Do you know when (which kernel version) this change in behavior occurred?
>>
>> Cheers,
>>
>> Michael
>>
>> Fernando Luis Vázquez Cao wrote:
>>> It used to be true that the command line arguments were not accessible
>>> when the process had been swapped out. In ancient kernels (circa 2.0.*)
>>> the problem was that the kernel relied on get_phys_addr to access the
>>> user space buffer, which stopped working as soon as the process was
>>> swapped out. Recent kernels use get_user_pages for the same purpose and
>>> thus they should not have that limitation.
>>>
>>> Signed-off-by: Fernando Luis Vazquez Cao <fernando-gVGce1chcLdL9jVzuh4AOg@public.gmane.org>
>>> ---
>>>
>>> --- proc.5.orig	2008-02-06 14:11:58.000000000 +0900
>>> +++ proc.5	2008-02-06 14:56:22.000000000 +0900
>>> @@ -87,12 +87,11 @@ plus one \fIunsigned long\fP value for e
>>>  The last entry contains two zeros.
>>>  .TP
>>>  .I /proc/[number]/cmdline
>>> -This holds the complete command line for the process, unless the whole
>>> -process has been swapped out or the process is a zombie.
>>> -In either of these latter cases, there is nothing in this file:
>>> -that is, a read on this file will return 0 characters.
>>> -The command line arguments appear in this file as a set of
>>> -null-separated strings, with a further null byte after the last string.
>>> +This holds the complete command line for the process, unless the process is a
>>> +zombie. In the latter case, there is nothing in this file: that is, a read on
>>> +this file will return 0 characters. The command line arguments appear in this
>>> +file as a set of null-separated strings, with a further null byte after the
>>> +last string.
>>>  .TP
>>>  .I /proc/[number]/cwd
>>>  This is a symbolic link to the current working directory of the process.
>>>
>>>
>>>
> 
> 

-- 
Michael Kerrisk
Maintainer of the Linux man-pages project
http://www.kernel.org/doc/man-pages/
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