[uml-devel] bug in uml?

[Erik P. <epa...@cs...>]

Hi,

	I've been working on getting checkpointing working under user-mode-linux,
and last night I found an interesting utility that can checkpoint any 
currently-running process all in userspace. /proc gives you most of what you
need, and the little bit it doesn't (current registers, position info for
the currently open fd's) it swipes out of the process with ptrace. Now, I 
could easily believe that the checkpointing wouldn't work under UML, so I'm
planning on adding the bits to /proc it needs so it doesn't have to mess with
ptrace(). However, I don't see any reason the restart code included here
wouldn't work - basically it creates a new stack to work out of, 
mmap()'s in the old process, opens up the old files and seeks in them, and
restores the registers.

The problem is that it segfaults restoring the last page of memory. Maybe
it's something wonky with the way UML handles it's stack, or maybe there's a
bug in the mmap() part of UML.

The code I was trying was here: 
ftp://ftp.gin.cz/pub/local/feela/src/freezer.tgz

It builds two apps, freeze and warm. I would 'freeze' a process that was
just doing a 
for(i=0;i<1000;i++){printf(i);sleep(1);}

under the host kernel and then 'warm' it under UML.

Thanks!

-Erik