Linux-Fsdevel Archive on lore.kernel.org
 help / color / Atom feed
From: Kirill Tkhai <ktkhai@virtuozzo.com>
To: Andrei Vagin <avagin@gmail.com>, adobriyan@gmail.com
Cc: "Eric W. Biederman" <ebiederm@xmission.com>,
	viro@zeniv.linux.org.uk, davem@davemloft.net,
	akpm@linux-foundation.org, christian.brauner@ubuntu.com,
	areber@redhat.com, serge@hallyn.com,
	linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
Subject: Re: [PATCH 00/23] proc: Introduce /proc/namespaces/ directory to expose namespaces lineary
Date: Fri, 7 Aug 2020 11:47:57 +0300
Message-ID: <2d65ca28-bcfa-b217-e201-09163640ebc2@virtuozzo.com> (raw)
In-Reply-To: <20200806080540.GA18865@gmail.com>

On 06.08.2020 11:05, Andrei Vagin wrote:
> On Mon, Aug 03, 2020 at 01:03:17PM +0300, Kirill Tkhai wrote:
>> On 31.07.2020 01:13, Eric W. Biederman wrote:
>>> Kirill Tkhai <ktkhai@virtuozzo.com> writes:
>>>
>>>> On 30.07.2020 17:34, Eric W. Biederman wrote:
>>>>> Kirill Tkhai <ktkhai@virtuozzo.com> writes:
>>>>>
>>>>>> Currently, there is no a way to list or iterate all or subset of namespaces
>>>>>> in the system. Some namespaces are exposed in /proc/[pid]/ns/ directories,
>>>>>> but some also may be as open files, which are not attached to a process.
>>>>>> When a namespace open fd is sent over unix socket and then closed, it is
>>>>>> impossible to know whether the namespace exists or not.
>>>>>>
>>>>>> Also, even if namespace is exposed as attached to a process or as open file,
>>>>>> iteration over /proc/*/ns/* or /proc/*/fd/* namespaces is not fast, because
>>>>>> this multiplies at tasks and fds number.
>>>>>
>>>>> I am very dubious about this.
>>>>>
>>>>> I have been avoiding exactly this kind of interface because it can
>>>>> create rather fundamental problems with checkpoint restart.
>>>>
>>>> restart/restore :)
>>>>
>>>>> You do have some filtering and the filtering is not based on current.
>>>>> Which is good.
>>>>>
>>>>> A view that is relative to a user namespace might be ok.    It almost
>>>>> certainly does better as it's own little filesystem than as an extension
>>>>> to proc though.
>>>>>
>>>>> The big thing we want to ensure is that if you migrate you can restore
>>>>> everything.  I don't see how you will be able to restore these files
>>>>> after migration.  Anything like this without having a complete
>>>>> checkpoint/restore story is a non-starter.
>>>>
>>>> There is no difference between files in /proc/namespaces/ directory and /proc/[pid]/ns/.
>>>>
>>>> CRIU can restore open files in /proc/[pid]/ns, the same will be with /proc/namespaces/ files.
>>>> As a person who worked deeply for pid_ns and user_ns support in CRIU, I don't see any
>>>> problem here.
>>>
>>> An obvious diffference is that you are adding the inode to the inode to
>>> the file name.  Which means that now you really do have to preserve the
>>> inode numbers during process migration.
>>>
>>> Which means now we have to do all of the work to make inode number
>>> restoration possible.  Which means now we need to have multiple
>>> instances of nsfs so that we can restore inode numbers.
>>>
>>> I think this is still possible but we have been delaying figuring out
>>> how to restore inode numbers long enough that may be actual technical
>>> problems making it happen.
>>
>> Yeah, this matters. But it looks like here is not a dead end. We just need
>> change the names the namespaces are exported to particular fs and to support
>> rename().
>>
>> Before introduction a principally new filesystem type for this, can't
>> this be solved in current /proc?
> 
> do you mean to introduce names for namespaces which users will be able
> to change? By default, this can be uuid.

Yes, I mean this.

Currently I won't give a final answer about UUID, but I planned to show some
default names, which based on namespace type and inode num. Completely custom
names for any /proc by default will waste too much memory.

So, I think the good way will be:

1)Introduce a function, which returns a hash/uuid based on ino, ns type and some static
random seed, which is generated on boot;

2)Use the hash/uuid as default names in newly create /proc/namespaces: pid-{hash/uuid(ino, "pid")}

3)Allow rename, and allocate space only for renamed names.

Maybe 2 and 3 will be implemented as shrinkable dentries and non-shrinkable.

> And I have a suggestion about the structure of /proc/namespaces/.
> 
> Each namespace is owned by one of user namespaces. Maybe it makes sense
> to group namespaces by their user-namespaces?
> 
> /proc/namespaces/
>                  user
>                  mnt-X
>                  mnt-Y
>                  pid-X
>                  uts-Z
>                  user-X/
>                         user
>                         mnt-A
>                         mnt-B
>                         user-C
>                         user-C/
>                                user
>                  user-Y/
>                         user

Hm, I don't think that user namespace is a generic key value for everybody.
For generic people tasks a user namespace is just a namespace among another
namespace types. For me it will look a bit strage to iterate some user namespaces
to build container net topology.

> Do we try to invent cgroupfs for namespaces?

Could you clarify your thought?

  reply index

Thread overview: 76+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-30 11:59 Kirill Tkhai
2020-07-30 11:59 ` [PATCH 01/23] ns: Add common refcount into ns_common add use it as counter for net_ns Kirill Tkhai
2020-07-30 13:35   ` Christian Brauner
2020-07-30 14:07     ` Kirill Tkhai
2020-07-30 15:59       ` Christian Brauner
2020-07-30 14:30   ` Christian Brauner
2020-07-30 14:34     ` Kirill Tkhai
2020-07-30 14:39       ` Christian Brauner
2020-07-30 11:59 ` [PATCH 02/23] uts: Use generic ns_common::count Kirill Tkhai
2020-07-30 14:30   ` Christian Brauner
2020-07-30 11:59 ` [PATCH 03/23] ipc: " Kirill Tkhai
2020-07-30 14:32   ` Christian Brauner
2020-07-30 11:59 ` [PATCH 04/23] pid: " Kirill Tkhai
2020-07-30 14:37   ` Christian Brauner
2020-07-30 11:59 ` [PATCH 05/23] user: " Kirill Tkhai
2020-07-30 14:46   ` Christian Brauner
2020-07-30 11:59 ` [PATCH 06/23] mnt: " Kirill Tkhai
2020-07-30 14:49   ` Christian Brauner
2020-07-30 11:59 ` [PATCH 07/23] cgroup: " Kirill Tkhai
2020-07-30 14:50   ` Christian Brauner
2020-07-30 12:00 ` [PATCH 08/23] time: " Kirill Tkhai
2020-07-30 14:52   ` Christian Brauner
2020-07-30 12:00 ` [PATCH 09/23] ns: Introduce ns_idr to be able to iterate all allocated namespaces in the system Kirill Tkhai
2020-07-30 12:23   ` Matthew Wilcox
2020-07-30 13:32     ` Kirill Tkhai
2020-07-30 13:56       ` Matthew Wilcox
2020-07-30 14:12         ` Kirill Tkhai
2020-07-30 14:15           ` Matthew Wilcox
2020-07-30 14:20             ` Kirill Tkhai
2020-07-30 12:00 ` [PATCH 10/23] fs: Rename fs/proc/namespaces.c into fs/proc/task_namespaces.c Kirill Tkhai
2020-07-30 12:00 ` [PATCH 11/23] fs: Add /proc/namespaces/ directory Kirill Tkhai
2020-07-30 12:18   ` Alexey Dobriyan
2020-07-30 13:22     ` Kirill Tkhai
2020-07-30 13:26   ` Christian Brauner
2020-07-30 14:30     ` Kirill Tkhai
2020-07-30 20:47   ` kernel test robot
2020-07-30 22:20   ` kernel test robot
2020-08-05  8:17   ` kernel test robot
2020-08-05  8:17   ` [RFC PATCH] fs: namespaces_dentry_operations can be static kernel test robot
2020-07-30 12:00 ` [PATCH 12/23] user: Free user_ns one RCU grace period after final counter put Kirill Tkhai
2020-07-30 12:00 ` [PATCH 13/23] user: Add user namespaces into ns_idr Kirill Tkhai
2020-07-30 12:00 ` [PATCH 14/23] net: Add net " Kirill Tkhai
2020-07-30 12:00 ` [PATCH 15/23] pid: Eextract child_reaper check from pidns_for_children_get() Kirill Tkhai
2020-07-30 12:00 ` [PATCH 16/23] proc_ns_operations: Add can_get method Kirill Tkhai
2020-07-30 12:00 ` [PATCH 17/23] pid: Add pid namespaces into ns_idr Kirill Tkhai
2020-07-30 12:00 ` [PATCH 18/23] uts: Free uts namespace one RCU grace period after final counter put Kirill Tkhai
2020-07-30 12:01 ` [PATCH 19/23] uts: Add uts namespaces into ns_idr Kirill Tkhai
2020-07-30 12:01 ` [PATCH 20/23] ipc: Add ipc " Kirill Tkhai
2020-07-30 12:01 ` [PATCH 21/23] mnt: Add mount " Kirill Tkhai
2020-07-30 12:01 ` [PATCH 22/23] cgroup: Add cgroup " Kirill Tkhai
2020-07-30 12:01 ` [PATCH 23/23] time: Add time " Kirill Tkhai
2020-07-30 13:08 ` [PATCH 00/23] proc: Introduce /proc/namespaces/ directory to expose namespaces lineary Christian Brauner
2020-07-30 13:38   ` Christian Brauner
2020-07-30 14:34 ` Eric W. Biederman
2020-07-30 14:42   ` Christian Brauner
2020-07-30 15:01   ` Kirill Tkhai
2020-07-30 22:13     ` Eric W. Biederman
2020-07-31  8:48       ` Pavel Tikhomirov
2020-08-03 10:03       ` Kirill Tkhai
2020-08-03 10:51         ` Alexey Dobriyan
2020-08-06  8:05         ` Andrei Vagin
2020-08-07  8:47           ` Kirill Tkhai [this message]
2020-08-10 17:34             ` Andrei Vagin
2020-08-11 10:23               ` Kirill Tkhai
2020-08-12 17:53                 ` Andrei Vagin
2020-08-13  8:12                   ` Kirill Tkhai
2020-08-14  1:16                     ` Andrei Vagin
2020-08-14 15:11                       ` Kirill Tkhai
2020-08-14 19:21                         ` Andrei Vagin
2020-08-17 14:05                           ` Kirill Tkhai
2020-08-17 15:48                             ` Eric W. Biederman
2020-08-17 17:47                               ` Christian Brauner
2020-08-17 18:53                                 ` Eric W. Biederman
2020-08-04  5:43     ` Andrei Vagin
2020-08-04 12:11       ` Pavel Tikhomirov
2020-08-04 14:47       ` Kirill Tkhai

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=2d65ca28-bcfa-b217-e201-09163640ebc2@virtuozzo.com \
    --to=ktkhai@virtuozzo.com \
    --cc=adobriyan@gmail.com \
    --cc=akpm@linux-foundation.org \
    --cc=areber@redhat.com \
    --cc=avagin@gmail.com \
    --cc=christian.brauner@ubuntu.com \
    --cc=davem@davemloft.net \
    --cc=ebiederm@xmission.com \
    --cc=linux-fsdevel@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=ptikhomirov@virtuozzo.com \
    --cc=serge@hallyn.com \
    --cc=viro@zeniv.linux.org.uk \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Fsdevel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-fsdevel/0 linux-fsdevel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-fsdevel linux-fsdevel/ https://lore.kernel.org/linux-fsdevel \
		linux-fsdevel@vger.kernel.org
	public-inbox-index linux-fsdevel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-fsdevel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git