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Fri, 31 Mar 2017 09:45:43 +0000 Subject: Re: [PATCH RESEND 2/2] pidns: Expose task pid_ns_for_children to userspace To: Andrei Vagin , Andrew Morton References: <149086931397.4388.9604947335273204415.stgit@localhost.localdomain> <149086967937.4388.471494976517194744.stgit@localhost.localdomain> <20170330150520.1bdf20e599ff464bda0776b9@linux-foundation.org> <20170331010409.GA22895@outlook.office365.com> CC: , , , , , , , , , , , , , From: Kirill Tkhai Message-ID: <0825f166-6f20-59a9-45a9-5ffe9009150e@virtuozzo.com> Date: Fri, 31 Mar 2017 12:45:40 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <20170331010409.GA22895@outlook.office365.com> X-Originating-IP: [195.214.232.6] X-ClientProxiedBy: HE1P190CA0018.EURP190.PROD.OUTLOOK.COM (10.172.123.28) To DB6PR0802MB2277.eurprd08.prod.outlook.com (10.172.227.150) X-MS-Office365-Filtering-Correlation-Id: 3b6dd50c-2bd4-485a-4430-08d4781ab3ee X-Microsoft-Antispam: UriScan:; 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20:ZXAGNN8qk/UJEE5pfYcwYKGLkNxW8rneqgUPU9/mJC4dDXWUh23aVQFRhoxuP6jlTBtl2BrBox9lL1iHESV2xUVDtOIH8TZ3lSWlxBUtuSAnjZsuCuWDg/N4DdeednjT0QxsiiUFlGafU31+Np6bWDUNEGUnkVZeM66ctMGiwAA= X-OriginatorOrg: virtuozzo.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 31 Mar 2017 09:45:43.1327 (UTC) X-MS-Exchange-CrossTenant-FromEntityHeader: Hosted X-MS-Exchange-Transport-CrossTenantHeadersStamped: DB6PR0802MB2277 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP On 31.03.2017 04:04, Andrei Vagin wrote: > On Thu, Mar 30, 2017 at 03:05:20PM -0700, Andrew Morton wrote: >> On Thu, 30 Mar 2017 13:27:59 +0300 Kirill Tkhai wrote: >> >>> pid_ns_for_children set by a task is known only to the task itself, >>> and it's impossible to identify it from outside. >>> >>> It's a big problem for checkpoint/restore software like CRIU, >>> because it can't correctly handle tasks, that do setns(CLONE_NEWPID) >>> in proccess of their work. >>> >>> This patch solves the problem, and it exposes pid_ns_for_children >>> to ns directory in standard way with the name "pid_for_children": >>> >>> ~# ls /proc/5531/ns -l | grep pid >>> lrwxrwxrwx 1 root root 0 Jan 14 16:38 pid -> pid:[4026531836] >>> lrwxrwxrwx 1 root root 0 Jan 14 16:38 pid_for_children -> pid:[4026532286] >>> >>> --- a/fs/proc/namespaces.c >>> +++ b/fs/proc/namespaces.c >>> @@ -23,6 +23,7 @@ static const struct proc_ns_operations *ns_entries[] = { >>> #endif >>> #ifdef CONFIG_PID_NS >>> &pidns_operations, >>> + &pidns_for_children_operations, >>> #endif >> >> This interface should be documented somewhere under Documentation/. >> But I can't immediately find where the /proc/pid/ns/ pseudo-files are >> documented... > > I know that they are documented in man7/namespaces.7 > > https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/man7/namespaces.7#n187 I suggest the below patch, but it's too early for the man description till the feature is in mainline, because the man page requires commit id of the feature. [PATCH] namespaces.7: Document the /proc/[pid]/ns/pid_for_children file Signed-off-by: Kirill Tkhai --- man7/namespaces.7 | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/man7/namespaces.7 b/man7/namespaces.7 index 6dfceaa2a..06041774f 100644 --- a/man7/namespaces.7 +++ b/man7/namespaces.7 @@ -125,6 +125,7 @@ lrwxrwxrwx. 1 mtk mtk 0 Apr 28 12:46 ipc \-> ipc:[4026531839] lrwxrwxrwx. 1 mtk mtk 0 Apr 28 12:46 mnt \-> mnt:[4026531840] lrwxrwxrwx. 1 mtk mtk 0 Apr 28 12:46 net \-> net:[4026531969] lrwxrwxrwx. 1 mtk mtk 0 Apr 28 12:46 pid \-> pid:[4026531836] +lrwxrwxrwx. 1 mtk mtk 0 Apr 28 12:46 pid_for_children -> pid:[4026531834] lrwxrwxrwx. 1 mtk mtk 0 Apr 28 12:46 user \-> user:[4026531837] lrwxrwxrwx. 1 mtk mtk 0 Apr 28 12:46 uts \-> uts:[4026531838] .fi @@ -186,7 +187,14 @@ This file is a handle for the network namespace of the process. .TP .IR /proc/[pid]/ns/pid " (since Linux 3.8)" .\" commit 57e8391d327609cbf12d843259c968b9e5c1838f -This file is a handle for the PID namespace of the process. +This file is a handle for the PID namespace of the process. It's +permanent during the whole process life. +.TP +.IR /proc/[pid]/ns/pid_for_children " (since Linux 4.12)" +.\" commit FIXME +This file is a handle for the PID namespace of a next born child +of the process. It's changed after unshare(2) and via setns(2), +so the file may differ from /proc/[pid]/ns/pid. .TP .IR /proc/[pid]/ns/user " (since Linux 3.8)" .\" commit cde1975bc242f3e1072bde623ef378e547b73f91