Kip's checkpointing code is now in the tree.

[Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>]

    Kip's checkpointing code is now in the tree.  Basically you use it
    by kldload'ing the checkpt.ko module, which should now be built 
    automatically.  You then ^E the program you want to checkpoint,
    and use the 'checkpt' utility in /usr/bin to resume it from the checkpoint
    file.  The program is *NOT* killed by this signal, it continues to run
    after the checkpoint file(s) have been generated.

    The checkpoint program is currently designed to work only with simple
    programs... it will save the signal, descriptors references regular 
    files, the VM state (anonymous memory), as well as any nominal
    file mappings, but it does not save sockets, pipes, or device descriptors,
    so while you can checkpoint a pipe sequence you can't really restore it.

    Please note that there are *SEVERE* security issues with this module.
    The module is not loaded into the kernel by default and, when loaded,
    can only be used by users in the wheel group.  You can change the group
    requirements with a sysctl (see the manual page for checkpt).  The
    security issues relate to the restoration of signals and file descriptors
    (in particular, the restoration system call will convert file handles
    into file descriptors which could potentially allow any file in the system
    to be accessed).  I've put in some basic security checks but they are not
    meant to be all encompassing!

    It is going into the tree now because Kip and I have done enough work on
    it that anyone else interested in working on it can theoretically dig in.
    Significant debugging is still in place.  We've left it as a module to 
    facilitate debugging.

    It should be useable for scientific applications now though I am not
    entirely certain that FP registers are saved and restored (maybe someone
    can play with that!).  It should already work considerably better then
    the linux equivalent what with the regular file descriptor save/restore
    capability.

    Any developer who wishes to work on the checkpointing module and related
    code is welcome to!

						-Matt