From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael Kerrisk (man-pages)" Subject: Re: [PATCH 0/5 RFC] Add an interface to discover relationships between namespaces Date: Tue, 26 Jul 2016 21:17:31 +0200 Message-ID: References: <20160721210650.GA10989@outlook.office365.com> <1515f5f2-5a49-fcab-61f4-8b627d3ba3e2@gmail.com> <87lh0pg8jx.fsf@x220.int.ebiederm.org> <44ca0e41-dc92-45b1-2a6c-c41a048a072d@gmail.com> <87r3ahepb4.fsf@x220.int.ebiederm.org> <20160726025455.GC26206@outlook.office365.com> <3390535b-0660-757f-aeba-c03d936b3485@gmail.com> <20160726182524.GA328@outlook.office365.com> Reply-To: mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20160726182524.GA328-1ViLX0X+lBJGNQ1M2rI3KwRV3xvJKrda@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Andrew Vagin Cc: Serge Hallyn , Andrey Vagin , Linux API , Linux Containers , LKML , "criu-GEFAQzZX7r8dnm+yROfE0A@public.gmane.org" , "Eric W. Biederman" , linux-fsdevel , James Bottomley , Alexander Viro List-Id: containers.vger.kernel.org Hello Andrew, On 26 July 2016 at 20:25, Andrew Vagin wrote: > On Tue, Jul 26, 2016 at 10:03:25AM +0200, Michael Kerrisk (man-pages) wrote: >> On 07/26/2016 04:54 AM, Andrew Vagin wrote: >> > On Mon, Jul 25, 2016 at 09:59:43AM -0500, Eric W. Biederman wrote: >> > > "Michael Kerrisk (man-pages)" writes: >> > >> > [snip] >> > >> > > [snip] >> > > > > > So, from my point of view, the important piece that was missing from >> > > > > > your commit message was the note to use readlink("/proc/self/fd/%d") >> > > > > > on the returned FDs. I think that detail needs to be part of the >> > > > > > commit message (and also the man page text). I think it even be >> > > > > > helpful to include the above program as part of the commit message: >> > > > > > it helps people more quickly grasp the API. >> > > > > >> > > > > Please, please make the standard way to compare these things fstat. >> > > > > That is much less magic than a symlink, and a little more future proof. >> > > > > Possibly even kcmp. >> > >> > I like the idea to use kcmp to compare namespaces. I am going to add this >> > functionality to kcmp and describe all these in the man page. >> >> Hi Andrey, >> >> Can you briefly sketch out the proposed API and how it would be used? >> I'd find it useful to see that even before the implementation. > > Sure. If a process wants to compare two namespaces, it needs to get file > descriptors for them (open /proc/PID/ns/XXX, use new ioctl-s, find a > process which has them), > and then it calls kcmp(pid1, pid2, KCMP_NSFD, ns_fd1, ns_fd2) > > For example, if we want to compare pid namespaces for 1 and 2 processes: > What's the purpose of the following line, and the use of 'pid' in the kcmp() call?: > pid = getpid(); > ns_fd1 = open("/proc/1/ns/pid") > ns_fd2 = open("/proc/2/ns/pid") > > if (!kcmp(pid, pid, KCMP_NSFD, ns_fd1, ns_fd2)) > printf("Both processes live in the same pid namespace\n"); Thanks, Michael