From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Hansen Subject: checkpointing VFS internals Date: Thu, 04 Dec 2008 07:01:24 -0800 Message-ID: <1228402884.13111.67.camel@nimitz> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: 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: "Serge E. Hallyn" Cc: containers List-Id: containers.vger.kernel.org Try the following: mkdir foo bar mount --bind foo bar (date; cat) > bar/file In another terminal: cat bar/file umount bar # should say busy umount -l bar cat bar/file # -EEXIST # ls -l /proc/`pidof cat`/fd/ total 0 lrwx------ 1 dave dave 64 2008-12-04 06:50 0 -> /dev/pts/22 l-wx------ 1 dave dave 64 2008-12-04 06:50 1 -> barfile lrwx------ 1 dave dave 64 2008-12-04 06:50 2 -> /dev/pts/22 You can still read and write to /proc/`pidof cat`/fd/1 as you would probably expect. But, there's no sign of the mount in /proc/mounts or /proc/$pid/{mounts,mountinfo,stats}. There's no apparent way to checkpoint this from userspace currently. This is basically the unlinked but open file problem, but with mounts. Should we work on getting the lazy unmounts in those files? Or, is this a case for checkpointing the mounts internally to the kernel just as we do with unlinked files? -- Dave