From mboxrd@z Thu Jan 1 00:00:00 1970 From: Nagarathnam Muthusamy Subject: Re: [PATCH v4] pidns: introduce syscall translate_pid Date: Mon, 16 Oct 2017 15:07:52 -0700 Message-ID: References: <150788678482.924140.11785205105514746135.stgit@buzz> <20171013160514.GA27812@redhat.com> <3bdb5341-9ae6-265a-ce5b-45c2cfc76fad@yandex-team.ru> <20171016143628.b2ef80a9ef16d4345889b4d9@linux-foundation.org> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20171016143628.b2ef80a9ef16d4345889b4d9-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org> Content-Language: en-US Sender: linux-api-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andrew Morton , Konstantin Khlebnikov Cc: Oleg Nesterov , linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Serge Hallyn , "Eric W. Biederman" , Eugene Syromiatnikov , prakash sangappa List-Id: linux-api@vger.kernel.org On 10/16/2017 02:36 PM, Andrew Morton wrote: > On Sat, 14 Oct 2017 11:17:47 +0300 Konstantin Khlebnikov wrote: > >>>>> pid_t translate_pid(pid_t pid, int source, int target); >>>>> >>>>> This syscall converts pid from source pid-ns into pid in target pid-ns. >>>>> If pid is unreachable from target pid-ns it returns zero. >>>>> >>>>> Pid-namespaces are referred file descriptors opened to proc files >>>>> /proc/[pid]/ns/pid or /proc/[pid]/ns/pid_for_children. Negative argument >>>>> refers to current pid namespace, same as file /proc/self/ns/pid. >>>>> >>>>> Kernel expose virtual pids in /proc/[pid]/status:NSpid, but backward >>>>> translation requires scanning all tasks. Also pids could be translated >>>>> by sending them through unix socket between namespaces, this method is >>>>> slow and insecure because other side is exposed inside pid namespace. >> Andrew asked why we might need this. >> >> Such conversion is required for interaction between processes across pid-namespaces. >> For example to identify process in container by pid file looking from outside. >> >> Two years ago I've solved this in project of mine with monstrous code which >> forks couple times just to convert pid, lucky for me performance wasn't important. > That's a single user who needed this a single time, and found a > userspace-based solution anyway. This is not exactly compelling! > > Is there a stronger case to be made? How does this change benefit our > users? Sell it to us! Oracle database is planning to use pid namespace for sandboxing database instances and they need an API similar to translate_pid to effectively translate process IDs from other pid namespaces. Prakash (cced in mail) can provide more details on this usecase. Thanks, Nagarathnam.