linux-kernel - Re: [PATCH 1/2] pidmap(2)

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Date:   Thu, 7 Sep 2017 12:47:11 +0300
From:   Alexey Dobriyan <adobriyan@...il.com>
To:     Djalal Harouni <tixxdz@...il.com>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Randy Dunlap <rdunlap@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tatsiana Brouka <Tatsiana_Brouka@...m.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Aliaksandr Patseyenak <Aliaksandr_Patseyenak1@...m.com>,
        Alexey Gladkov <gladkov.alexey@...il.com>
Subject: Re: [PATCH 1/2] pidmap(2)

On 9/7/17, Djalal Harouni <tixxdz@...il.com> wrote:
> Hi Alexey,
>
> On Thu, Sep 7, 2017 at 4:04 AM, Andy Lutomirski <luto@...capital.net>
> wrote:
>> On Wed, Sep 6, 2017 at 2:04 AM, Alexey Dobriyan <adobriyan@...il.com>
>> wrote:
>>> On 9/6/17, Randy Dunlap <rdunlap@...radead.org> wrote:
>>>> On 09/05/17 15:53, Andrew Morton wrote:
> [...]
>>>>
>>>> also, I expect that the tiny kernel people will want kconfig options
>>>> for
>>>> these syscalls.
>>>
>>> We'll add it but the question if it is a good idea. Ideally these system
>>> calls
>>> should be mandatory and /proc optional.
>>>
>>> $ size kernel/pidmap.o fs/fdmap.o
>>>    text    data     bss     dec     hex filename
>>>     560       0       0     560     230 kernel/pidmap.o
>>>     617       0       0     617     269 fs/fdmap.o
>>
>> After much discussion at LPC/KS last year, I thought the idea was to
>> try to speed up /proc rather than replacing it outright.  The two
>> specific ideas I recall were:
>>
>> 1. Add a syscall like readfileat() that you can use to, in a single
>> operation, open, read, and close a /proc file (or other file).  This
>> should vastly reduce locking and RCU overhead.
>>
>> 2. Add a /proc file that has a nice binary format for task info.
>> (nl_attr?)
>>
>> I don't see why pidmap() deserves to be significantly faster than
>> getdents().
>>
>> Also, a pidmap() syscall like this inherently bypasses any security
>> restrictions implied by the way that /proc is mounted.  It can respect
>> hidepid, but hidepid (as a per-namespace concept) is an enormous turd
>> that badly needs to be deprecated, and Djalal is working on exactly
>> that.
>
> Yes as noted by Andy, me and Alexey Gladkov are working on modernizing
> procfs [1] and to reduce/remove ties within pid namespaces which has lot
> of problems now.
> ...

Kudos for digging into this mess.
But the question will remain: how get pids of existing processes quickly.