From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Serge E. Hallyn" Subject: Re: [BIG RFC] Filesystem-based checkpoint Date: Fri, 31 Oct 2008 08:48:41 -0500 Message-ID: <20081031134841.GA11140@us.ibm.com> References: <1225219047.12673.182.camel@nimitz> <1225411757.12673.383.camel@nimitz> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: 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: "Eric W. Biederman" Cc: containers , Dave Hansen List-Id: containers.vger.kernel.org Quoting Eric W. Biederman (ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org): > With a file descriptor I can push the data onto a network socket and > the receiving process is on another computer. 0 copies, 0 trips > to user space. I'm not certain how you would achieve that with filesystem > approach. This has been Oren's most convincing argument for all sorts of little choices (his precise data format, the use of an fd and cr_kwrite()). I wonder (a) what neat things Dave could come up with to to bridge that gap, and (b) how much of that gap becomes less meaningful with a proper use of pre-dump (and post-dump). > >> Reading the memory of another process is a problem, to the point > >> that the /proc//mem interface has been removed from the kernel. > > > > Yes, this is certainly true. All of the ptrace-related security issues > > surely tell us something. But, I'm not sure of your point here. Are > > you saying that using sys_checkpoint() to dump a process's pages is > > inherently safer than approach that uses a filesystem in order to do the > > same? > > I'm saying inspecting another process is a very racy operation so something > we need to be especially careful with. I don't see any difference there between Dave's and Oren's approaches. In either case, the container is frozen while the kernel walks the container's task's pages and dumps them... somewhere. -serge