[Devel] Re: cryo and mm->arg_start

[Serge E. Hallyn]

Quoting Matt Helsley (matthltc at us.ibm.com):
> 
> On Fri, 2008-07-11 at 09:38 -0700, Dave Hansen wrote:
> > On Fri, 2008-07-11 at 08:13 -0500, Serge E. Hallyn wrote:
> > > 
> > > One thing we could do here is to start extending the cryo approach
> > > with Eric's checkpoint-as-a-coredump (caac?).  We generate the
> > > tiniest of coredumps which, at first, contains nothing but
> > > mm->arg_start and maybe a process id.  It would be simplest if
> > > it also contained a filename for the real executable,
> > 
> > The exec model sounds reasonable to me.
> >
> > But, I think the filename of the exe is going to have to be in the
> > checkpoint *already*.  It is mapped by at least one of the VMAs, and
> > will probably be dumped as a normal file-backed area.  
> 
> 	Yes, the file that backed the exec will be there. Note that thanks to
> "stacking" filesystems the path to the file backing the exe is not
> _always_ going to be the same as the path to the file which userspace
> exec'd in the first place. You can see this by comparing
> the /proc/<pid>/exe symlink with the file backing the VMA.
> 
> 	This is important to any program which checks the /proc/self/exe
> symlink to find out where it's installed (Java does this, for example).
> I think it's possible to do this with a binfmt -- it's just one more
> detail to remember.
> 
> Cheers,
> 	-Matt

Let's say that before starting my checkpointable job, I did

	mount -t ecryptfs /home/hallyn /home/hallyn

Now if the checkpointable job is /home/hallyn/somelongjob, then I think
it's fair to say that restart can fail if /home/hallyn at the restart
machine isn't ecryptfs-mounted.

In that case, would you still think there is a problem?

On the other hand, if the checkpointable job did the ecryptfs mount
itself, then it would be expected that at restart the ecryptfs mount
would be remounted.  How that would be done I have no idea offhand.

thanks,
-serge
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