[Devel] Re: [RFC v11][PATCH 00/13] Kernel based checkpoint/restart

[Dave Hansen]

Andrew,

I just realized that you weren't cc'd on these when they were posted.

Can we give them a run in -mm?  As far as I know, all review comments
have been addressed and there's nothing outstanding.

On Fri, 2008-12-05 at 12:31 -0500, Oren Laadan wrote:
> Checkpoint-restart (c/r): fixed races in file handling (comments from
> from Al Viro). Updated and tested against v2.6.28-rc7 (feaf384...)
> 
> We'd like these to make it into -mm. This version addresses the
> last of the known bugs. Please pull at least the first 11 patches,
> as they are similar to before.
> 
> Patches 1-11 are stable, providing self- and external- c/r of a
> single process.
> Patches 12 and 13 are newer, adding support for c/r of multiple
> processes.
> 
> The git tree tracking v11, branch 'ckpt-v11' (and older versions):
> 	git://git.ncl.cs.columbia.edu/pub/git/linux-cr.git
> 
> Restarting multiple processes requires 'mktree' userspace tool:
> 	git://git.ncl.cs.columbia.edu/pub/git/user-cr.git
> 
> Oren.
> 
> 
> --
> Why do we want it?  It allows containers to be moved between physical
> machines' kernels in the same way that VMWare can move VMs between
> physical machines' hypervisors.  There are currently at least two
> out-of-tree implementations of this in the commercial world (IBM's
> Metacluster and Parallels' OpenVZ/Virtuozzo) and several in the academic
> world like Zap.
> 
> Why do we need it in mainline now?  Because we already have plenty of
> out-of-tree ones, and  want to know what an in-tree one will be like.   :)  
> What *I* want right now is the extra review and scrutiny that comes with
> a mainline submission to make sure we're not going in a direction
> contrary to the community.
> 
> This only supports pretty simple apps.  But, I trust Ingo when he says:
> >> > > Generally, if something works for simple apps already (in a robust, 
> >> > > compatible and supportable way) and users find it "very cool", then 
> >> > > support for more complex apps is not far in the future.  but if you
> >> > > want to support more complex apps straight away, it takes forever and
> >> > > gets ugly.
> 
> We're *certainly* going to be changing the ABI (which is the format of
> the checkpoint).  I'd like to follow the model that we used for
> ext4-dev, which is to make it very clear that this is a development-only
> feature for now.  Perhaps we do that by making the interface only
> available through debugfs or something similar for now.  Or, reserving
> the syscall numbers but require some runtime switch to be thrown before
> they can be used.  I'm open to suggestions here.
> --
> 
> --
> Todo:
> - Add support for x86-64 and improve ABI
> - Refine or change syscall interface
> - Handle multiple namespaces in a container (e.g. save the filesystem
>   namespaces state with the file descriptors)
> - Security (without CAPS_SYS_ADMIN files restore may fail)
> 
> Changelog:
> 
> [2008-Dec-05] v11:
>   - Use contents of 'init->fs->root' instead of pointing to it
>   - Ignore symlinks (there is no such thing as an open symlink)
>   - cr_scan_fds() retries from scratch if it hits size limits
>   - Add missing test for VM_MAYSHARE when dumping memory
>   - Improve documentation about: behavior when tasks aren't fronen,
>     life span of the object hash, references to objects in the hash
> 
> [2008-Nov-26] v10:
>   - Grab vfs root of container init, rather than current process
>   - Acquire dcache_lock around call to __d_path() in cr_fill_name()
>   - Force end-of-string in cr_read_string() (fix possible DoS)
>   - Introduce cr_write_buffer(), cr_read_buffer() and cr_read_buf_type()
> 
> [2008-Nov-10] v9:
>   - Support multiple processes c/r
>   - Extend checkpoint header with archtiecture dependent header 
>   - Misc bug fixes (see individual changelogs)
>   - Rebase to v2.6.28-rc3.
> 
> [2008-Oct-29] v8:
>   - Support "external" checkpoint
>   - Include Dave Hansen's 'deny-checkpoint' patch
>   - Split docs in Documentation/checkpoint/..., and improve contents
> 
> [2008-Oct-17] v7:
>   - Fix save/restore state of FPU
>   - Fix argument given to kunmap_atomic() in memory dump/restore
> 
> [2008-Oct-07] v6:
>   - Balance all calls to cr_hbuf_get() with matching cr_hbuf_put()
>     (even though it's not really needed)
>   - Add assumptions and what's-missing to documentation
>   - Misc fixes and cleanups
> 
> [2008-Sep-11] v5:
>   - Config is now 'def_bool n' by default
>   - Improve memory dump/restore code (following Dave Hansen's comments)
>   - Change dump format (and code) to allow chunks of <vaddrs, pages>
>     instead of one long list of each
>   - Fix use of follow_page() to avoid faulting in non-present pages
>   - Memory restore now maps user pages explicitly to copy data into them,
>     instead of reading directly to user space; got rid of mprotect_fixup()
>   - Remove preempt_disable() when restoring debug registers
>   - Rename headers files s/ckpt/checkpoint/
>   - Fix misc bugs in files dump/restore
>   - Fixes and cleanups on some error paths
>   - Fix misc coding style
> 
> [2008-Sep-09] v4:
>   - Various fixes and clean-ups
>   - Fix calculation of hash table size
>   - Fix header structure alignment
>   - Use stand list_... for cr_pgarr
> 
> [2008-Aug-29] v3:
>   - Various fixes and clean-ups
>   - Use standard hlist_... for hash table
>   - Better use of standard kmalloc/kfree
> 
> [2008-Aug-20] v2:
>   - Added Dump and restore of open files (regular and directories)
>   - Added basic handling of shared objects, and improve handling of
>     'parent tag' concept
>   - Added documentation
>   - Improved ABI, 64bit padding for image data
>   - Improved locking when saving/restoring memory
>   - Added UTS information to header (release, version, machine)
>   - Cleanup extraction of filename from a file pointer
>   - Refactor to allow easier reviewing
>   - Remove requirement for CAPS_SYS_ADMIN until we come up with a
>     security policy (this means that file restore may fail)
>   - Other cleanup and response to comments for v1
> 
> [2008-Jul-29] v1:
>   - Initial version: support a single task with address space of only
>     private anonymous or file-mapped VMAs; syscalls ignore pid/crid
>     argument and act on current process.
> 
> --
> At the containers mini-conference before OLS, the consensus among
> all the stakeholders was that doing checkpoint/restart in the kernel
> as much as possible was the best approach.  With this approach, the
> kernel will export a relatively opaque 'blob' of data to userspace
> which can then be handed to the new kernel at restore time.
> 
> This is different than what had been proposed before, which was
> that a userspace application would be responsible for collecting
> all of this data.  We were also planning on adding lots of new,
> little kernel interfaces for all of the things that needed
> checkpointing.  This unites those into a single, grand interface.
> 
> The 'blob' will contain copies of select portions of kernel
> structures such as vmas and mm_structs.  It will also contain
> copies of the actual memory that the process uses.  Any changes
> in this blob's format between kernel revisions can be handled by
> an in-userspace conversion program.
> 
> This is a similar approach to virtually all of the commercial
> checkpoint/restart products out there, as well as the research
> project Zap.
> 
> These patches basically serialize internel kernel state and write
> it out to a file descriptor.  The checkpoint and restore are done
> with two new system calls: sys_checkpoint and sys_restart.
> 
> In this incarnation, they can only work checkpoint and restore a
> single task. The task's address space may consist of only private,
> simple vma's - anonymous or file-mapped. The open files may consist
> of only simple files and directories.
> --
> 
> --
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-- Dave

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