Quoting Louis Rilling (Louis.Rilling@xxxxxxxxxxx): > Hi Serge, > > On 30/11/09 14:22 -0600, Serge E. Hallyn wrote: > > We currently checkpoint and restart unix98 ptys in the kernel. > > So what do we want to do about the userspace part? In particular, > > if I run the following test program and checkpoint it, it > > has `tty` open. What do we want to do about that? > > > > Just having user-cr/restart.c take an option to mount a new > > instance of devpts isn't enough - we don't get hooked up to > > restart.c's stdin/out obviously, and restart succeeds but the > > restarted program exists with -EIO. At the same time, just > > doing a cradvise type of thing to plug fds 0,1,2 suffice for > > this testcase, but not for something more complicated which > > also has other unix98 ptys open. > > In Kerrighed we are implementing something à-la-cradvise: we allow the > caller of sys_restart() to give replacement fds for arbitrary files. To achieve > this, each checkpointed file descriptor (struct file) has a unique key, and > sys_restart() takes a substitution table in parameter, where an entry is a > pair (key, fd). Thanks - that sounds somewhat like what I was leaning toward last night. In particular, I was thinking that a user-space tool could walk over the checkpoint image and replace certain checkpointed filenames with a string like "\0RESERVED_FD0". Sys_restart() would see that filename at restore_file() and plug in the coordinator task's fd 0. The thing I don't like about it is that I'm replacing pathnames, and so I worry that applications playing with mounts namespaces will be a problem for the program rewriting the checkpoint image. Not insurmountable, but requiring a lot more work... > In Kerrighed sys_checkpoint() exports a human-readable table of checkpointed > file descriptors, with types, fd in each checkpointed task, etc. > With Oren's patchset, I presume that some userspace tool could extract such a > table from the checkpoint. Yeah, I guess such a program for analyzing and rewriting resources in a checkpoint image would be very useful. Could perhaps also be used for network interfaces, internal mounts, uids, in-kernel keyring... > Hope this makes the discussion progress... Yup, thanks! -serge _______________________________________________ Containers mailing list Containers@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/containers
