linux-kernel - Re: + proc-fix-the-threaded-proc-self.patch added to -mm tree

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Message-ID: <m1ve7mehcm.fsf@ebiederm.dsl.xmission.com>
Date:	Wed, 28 Nov 2007 04:31:53 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Albert Cahalan <acahalan@...il.com>,
	Guillaume Chazarain <guichaz@...oo.fr>,
	akpm@...ux-foundation.org, mm-commits@...r.kernel.org,
	oleg@...sign.ru, rjw@...k.pl, roland@...hat.com, xemul@...nvz.org,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ulrich Drepper <drepper@...hat.com>
Subject: Re: + proc-fix-the-threaded-proc-self.patch added to -mm tree

Ingo Molnar <mingo@...e.hu> writes:

> * Albert Cahalan <acahalan@...il.com> wrote:
>
>> On Nov 27, 2007 7:49 PM, Guillaume Chazarain <guichaz@...oo.fr> wrote:
>> > akpm@...ux-foundation.org wrote:
>> >
>> > > We may be stuck with the current broken behavior for backwards
>> > > compatibility reasons but lets try fixing our ancient bug for the 2.6.25
>> > > time frame and see if anyone screams.
>> 
>> It's not broken. It's just not the feature you're looking for.
>
> well it's quite broken at the moment and we are looking for solutions 
> not for a blame game :-) You might have read the thread where i describe 
> what i had to go through to do something fairly trivial.

Yes.

In a lot of ways if you access /proc/self and you get back information
that does not correspond to yourself the result is nonsense.  Which
is a fairly mighty problem.

I'm still trying to understand which will break user space more,
adding /proc/task or changing /proc/self.

>> This one is probably best:
>> /proc/task -> 123/task/456
>> (with both numbers showing)
>
> this sounds good to me. If it's a symlink then there's not much other 
> choice because the thread PIDs do not even show up under /proc anymore.

The name sounds good to me.

I am not certain the two components make sense as we have a possible
permission problem where it is remotely possible that a task will
have permission to access /proc/<tid> but not /proc/<tgid>.

We certainly need to think through that case before making it
to a stable kernel.

The reason I care is that we need to fix /proc/mounts.  So once we
have /proc/task we can also have change /proc/mounts to
be a symlink to /proc/task/mounts. 

Once we get the /proc/mounts thing sorted out.  There are several
other entries in /proc that need to that need to follow in it's wake
as they also become per namespace.  /proc/net and /proc/sysvipc for
starters.

Eric
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