Re: [PATCH v21 00/100] Kernel based checkpoint/restart

[Oren Laadan <orenl@cs.columbia.edu>]

Forgot to mention - based on 2.6.34-rc5.

Oren.

Oren Laadan wrote:
> Hi Andrew,
> 
> Here is the next version of the checkpoint/restart patchset.  This
> version moves portions of checkpoint code closer to where they belong.
> 
> As a convenience we've collected a rough table of contents showing
> places to start for some reviewers with limited time and/or scope
> (see below).
> 
> Thanks to Jamie, Nick, Andreas, and all who helped review the last few
> versions, and thanks in advance for comments on this version.
> 
> We'll be very grateful if this can get a spin in -mm to get some wider
> testing in the meantime.
> 
> Thanks,
> 
> The Checkpoint/Restart developers.
> 
> ---
> 
> Linux Checkpoint-Restart:
>  web, wiki:	http://www.linux-cr.org
>  bug track:	https://www.linux-cr.org/redmine
> 
> The repositories for the project are in:
>  kernel:	http://www.linux-cr.org/git/?p=linux-cr.git;a=summary
>  user tools:	http://www.linux-cr.org/git/?p=user-cr.git;a=summary
>  tests suite:	http://www.linux-cr.org/git/?p=tests-cr.git;a=summary
> 
> ---
> 
> TABLE OF CONTENTS
> 
> Patches                 Area/Role
> -------------------------------------------------------------------------
> 11,20                   Documentation (eclone, c/r)
> 8-11,21,22,27,28        Syscall gluey bits
> 
> 12                      Arch Maintainers
> 8,22-24                         x86-32/64
> 9,58,60                         s390
> 10,84-88                        powerpc
> 
> 14,61-63,69,70,         Security
> 71,89-92,
> 
> 33,34,35                Generic c/r
>                         (shared "object" hash, leak detection, deferqueues)
> 
> 25,27-31                Processes
> 5-7                       fork (eclone)
> 39-41,45,46               memory
> 13,18,51,52,54,           namespaces
> 81-83,94
> 53-57                     ipc
> 64-67                     signals
> 1-4,70,83                 pids, pgids, tids, tgids (eclone or pidns)
> 14,61,62,69               creds, capabilities, uids, gids
> 71                        sockets
> 76-78                     terminals (specifically pty)
> 27,28,32                  futexes (27,28 relate to futex syscalls restart)
> 
> 39-41,45,46,55            mm (basically process memory)
> 
> 15-17                   Cgroups
> 
> 71-75,93-99             Networking
> 
> 19,36-38,42-44,         Filesystems (also pseudo-filesystems, anon_inodes)
> 47-50,63,76-77,
> 79-82
> 
> Some patches show up in multiple places because they are functionally
> related even though they cross Area/Role boundaries. While we've done our
> best to make the table above comprehensive, it's entirely conceivable that
> we've neglected a small piece of a largely unrelated patch. Please feel
> free to point these out to Matt Helsley <matthltc@us.ibm.com> since he's
> largely responsible for this table.
> 
> ---
> 
> CHANGELOG:
> 
> [2010-Apr-30] v21
>   - Add relevant maintainers/lists as Cc: in patch descriptions
>   - Reorganize code: move checkpoint/* to kernel/checkpoint/*
>   - Reorganize filesystem code into fs/*
>   - Merge files dump/restore into a single patch
>   - Merge mm dump/restore into a single patch
>   - Move utsns c/r code from checkpoint/namespace.c to kernel/utsname*.c
>   - [Matt Helsley] Move the signal c/r changes to kernel/signal.c
>   - Move userns c/r code from to kernel/{user,cred,user_namespace}.c
>   - Assorted fixes to bisectability of patchset
>   - Do not include checkpoint_hdr.h explicitly
>   - Subsystems/modules register shared objects types for c/r
>   - [Serge Hallyn] CONFIG_SECURITY_FILE_CAPABILITIES has been gone awhile
>   - [Dan Smith] Unbreak compiling with CONFIG_CHECKPOINT=n or CONFIG_NET_NS=n
>   - [Dan Smith] Clean up the error path in restore_veth()
>   - [Dan Smith] Fix acquiring socket lock before reading RTNETLINK response
>   - [Dan Smith] Skip down interfaces (v2)
>   - [Dan Smith] Export net checkpoint fns
>   - [Dan Smith] Add CHECKPOINT_NETNS flag
>   - [Dan Smith] Netdev restore function dispatching from a table
>   - [Dan Smith] Comment on controverial determination of "initial netns"
>   - [Dan Smith] Simplify the E2BIG error handling in netdev c/r
>   - [Dan Smith] Remove a redundant check for checkpoint support per-device
>   - [Nathan Lynch] powerpc: fix build break with CONFIG_CHECKPOINT=n 
>   - [Matt Helsley] Eventfd: add missing spin locks around eventfd checkpoint
>   - [Matt Helsley] Put file_ops->checkpoint under CONFIG_CHECKPOINT
>   - [Dan Smith] Fix build when CONFIG_INET=n
>   - [Dan Smith] Disable softirqs when taking the socket queue lock
>   - Replace __initcall() with late_initcall()
>   - [Serge Hallyn] Remove [] following individual ops definitions.
>   - [Serge Hallyn] Fix compilation for when CONFIG_USER_NS=y
>   - [Serge Hallyn] handle CONFIG_{SYSVIPC,SYSVIPC,POSIX_MQUEUE}=n
>   - [Serge Hallyn] Remove namespace.o from kernel/checkpoint/Makefile
>   - [Stanislav O. Bezzubtsev] Fix omitted parameter name error
>   - Put file_ops->checkpoint under CONFIG_CHECKPOINT
>   - [Serge] Print out full path of file which crossed mnt_ns
>   - Update Documentation/filesystem/vfs.txt
>   - Restore_obj() to tolerate a preexisting object in the hash
>   - Add ckpt_obj_del() to objhash for handling error conditions
>   - [Serge Hallyn] Replace BUG_ON() in obj_new with error returns
>   - [Matt Helsley] Move CKPT_CTX_ERROR* definitions to first use.
>   - [Nathan Lynch] x86: use task_user_gs to checkpoint gs
>   - Complain if checkpoint_hdr.h included without CONFIG_CHECKPOINT
>   - Introduce kernel_write(), fix kernel_read()
>   - Consolidate ckpt_read/write with kernel_read/write
>   - [Christoffer Dall] Fix trivial bug in ckpt_msg macro
>   - [Serge Hallyn] user/group: address dhowells feedback
>  
> [2010-Mar-16] v20
>  BUG FIXES (only)
>   - [Serge Hallyn] Fix unlabeled restore case
>   - [Serge Hallyn] Always restore msg_msg label
>   - [Serge Hallyn] Selinux prevents msgrcv on restore message queues?
>   - [Serge Hallyn] save_access_regs for self-checkpoint
>   - [Serge Hallyn] send uses_interp=1 to arch_setup_additional_pages
>   - Fix "scheduling in atomic" while restoring ipc (sem, shm, msg)
>   - Cleanup: no need to restore perm->{id,key,seq}
>   - Fix sysvipc=n compile
>   - Make uts_ns=n compile
>   - Only use arch_setup_additional_pages() if supported by arch
>   - Export key symbols to enable c/r from kernel modules
>   - Avoid crash if incoming object doesn't have .restore
>   - Replace error_sem with an event completion
>   - [Serge Hallyn] Change sysctl and default for unprivileged use
>   - [Nathan Lynch] Use syscall_get_error
>   - Add entry for checkpoint/restart in MAINTAINERS 
> 
> [2010-Feb-19] v19
>  NEW FEATURES
>   - Support for x86-64 architecture
>   - Support for c/r of LSM (smack, selinux)
>   - Support for c/r of task fs_root and pwd
>   - Support for c/r of epoll
>   - Support for c/r of eventfd
>   - Enable C/R while executing over NFS
>   - Preliminary c/r of mounts namespace
>   - Add @logfd argument to sys_{checkpoint,restart} prototypes
>   - Define new api for error and debug logging
>   - Restart to handle checkpoint images lacking {uts,ipc}-ns
>   - Refuse to checkpoint if monitoring directories with dnotify
>   - Refuse to checkpoint if file locks and leases are held
>   - Refuse to checkpoint files with f_owner 
>  OTHER CHANGES
>   - Rebase to kernel 2.6.33-rc8
>   - Settled version of new sys_eclone()
>   - [Serge Hallyn] Fix potential use-before-set return (vdso)
>   - Update documentation and examples for new syscalls API (doc)
>   - [Liu Alexander] Fix typos (doc)
>   - [Serge Hallyn] Update checkpoint image format (doc)
>   - [Serge Hallyn] Use ckpt_err() to for bad header values
>   - sys_{checkpoint,restart} to use ptregs prototype
>   - Set ctx->errno in do_ckpt_msg() if needed
>   - Fix up headers so we can munge them for use by userspace
>   - Multiple fixes to _ckpt_write_err() and friends
>   - [Matt Helsley] Add cpp definitions for enums
>   - [Serge Hallyn] Add global section container to image format
>   - [Matt Helsley] Fix total byte read/write count for large images
>   - ckpt_read_buf_type() to accept max payload (excludes ckpt_hdr)
>   - [Serge Hallyn] Use ckpt_err() for arch incompatbilities
>   - Introduce walk_task_subtree() to iterate through descendants
>   - Call restore_notify_error for restart (not checkpoint !)
>   - Make kread/kwrite() abort if CKPT_CTX_ERROR is set
>   - [Serge Hallyn] Move init_completion(&ctx->complete) to ctx_alloc
>   - Simplify logic of tracking restarting tasks (->ctx)
>   - Coordinator kills descendants on failure for proper cleanup
>   - Prepare descendants needs PTRACE_MODE_ATTACH permissions
>   - Threads wait for entire thread group before restoring
>   - Add debug process-tree status during restart
>   - Fix handling of bogus pid arg to sys_restart
>   - In reparent_thread() test for PF_RESTARTING on parent
>   - Keep __u32s in even groups for 32-64 bit compatibility
>   - Define ckpt_obj_try_fetch
>   - Disallow zero or negative objref during restart
>   - Check for valid destructor before calling it (deferqueue)
>   - Fix false negative of test for unlinked files at checkpoint
>   - [Serge Hallyn] Rename fs_mnt to root_fs_path
>   - Restore thread/cpu state early
>   - Ensure null-termination of file names read from image
>   - Fix compile warning in restore_open_fname()
>   - Introduce FOLL_DIRTY to follow_page() for "dirty" pages
>   - [Serge Hallyn] Checkpoint saved_auxv as u64s
>   - Export filemap_checkpoint()
>   - [Serge Hallyn] Disallow checkpoint of tasks with aio requests
>   - Fix compilation failure when !CONFIG_CHEKCPOINT (regression)
>   - Expose page write functions
>   - Do not hold mmap_sem while checkpointing vma's
>   - Do not hold mmap_sem when reading memory pages on restart
>   -  Move consider_private_page() to mm/memory.c:__get_dirty_page()
>   - [Serge Hallyn] move destroy_mm into mmap.c and remove size check
>   - [Serge Hallyn] fill vdso (syscall32_setup_pages) for TIF_IA32/x86_64
>   - [Serge Hallyn] Fix return value of read_pages_contents()
>   - [Serge Hallyn] Change m_type to long, not int (ipc)
>   - Don't free sma if it's an error on restore
>   - Use task->saves_sigmask and drop task->checkpoint_data
>   - [Serge Hallyn] Handle saved_sigmask at checkpoint
>   - Defer restore of blocked signals mask during restart
>   - Self-restart to tolerate missing PGIDs
>   - [Serge Hallyn] skb->tail can be offset
>   - Export and leverage sock_alloc_file()
>   - [Nathan Lynch] Fix net/checkpoint.c for 64-bit
>   - [Dan Smith] Unify skb read/write functions and handle fragmented buffers
>   - [Dan Smith] Update buffer restore code to match the new format
>   - [Dan Smith] Fix compile issue with CONFIG_CHECKPOINT=n
>   - [Dan Smith] Remove an unnecessary check on socket restart
>   - [Dan Smith] Pass the stored sock->protocol into sock_create() on restore
>   - Relax tcp.window_clamp value in INET restore
>   - Restore gso_type fields on sockets and buffers for proper operation
>   - Fix broken compilation for no-c/r architectures
>   - Return -EBUSY (not BUG_ON) if fd is gone on restart
>   - Fix the chunk size instead of auto-tune (epoll) 
>  ARCH: x86 (32,64)
>   - Use PTREGSCALL4 for sys_{checkpoint,restart}
>   - Remove debug-reg support (need to redo with perf_events)
>   - [Serge Hallyn] Support for ia32 (checkpoint, restart)
>   - Split arch/x86/checkpoint.c to generic and 32bit specific parts
>   - sys_{checkpoint,restore} to use ptregs
>   - Allow X86_EFLAGS_RF on restart
>   - [Serge Hallyn] Only allow 'restart' with same bit-ness as image.
>   - Move checkpoint.c from arch/x86/mm->arch/x86/kernel 
>  ARCH: s390 [Serge Hallyn]
>   - Define s390x sys_restart wrapper
>   - Fixes to restart-blocks logic and signal path
>   - Fix checkpoint and restart compat wrappers
>   - sys_{checkpoint,restore} to use ptregs
>   - Use simpler test_task_thread to test current ti flags
>   - Fix 31-bit s390 checkpoint/restart wrappers
>   - Update sys_checkpoint (do_sys_checkpoint on all archs)
>   - [Oren Laadan] Move checkpoint.c from arch/s390/mm->arch/s390/kernel 
>  ARCH: powerpc [Nathan Lynch]
>   - [Serge Hallyn] Add hook task_has_saved_sigmask()
>   - Warn if full register state unavailable
>   - Fix up checkpoint syscall, tidy restart
>   - [Oren Laadan] Move checkpoint.c from arch/powerpc/{mm->kernel} 
> 
> [2009-Sep-22] v18
>  NEW FEATURES
>   - [Nathan Lynch] Re-introduce powerpc support
>   - Save/restore pseudo-terminals
>   - Save/restore (pty) controlling terminals
>   - Save/restore restore PGIDs
>   - [Dan Smith] Save/restore unix domain sockets
>   - Save/restore FIFOs
>   - Save/restore pending signals
>   - Save/restore rlimits
>   - Save/restore itimers
>   - [Matt Helsley] Handle many non-pseudo file-systems
>  OTHER CHANGES
>   - Rename headerless struct ckpt_hdr_* to struct ckpt_*
>   - [Nathan Lynch] discard const from struct cred * where appropriate
>   - [Serge Hallyn][s390] Set return value for self-checkpoint 
>   - Handle kmalloc failure in restore_sem_array()
>   - [IPC] Collect files used by shm objects
>   - [IPC] Use file (not inode) as shared object on checkpoint of shm
>   - More ckpt_write_err()s to give information on checkpoint failure
>   - Adjust format of pipe buffer to include the mandatory pre-header
>   - [LEAKS] Mark the backing file as visited at chekcpoint
>   - Tighten checks on supported vma to checkpoint or restart
>   - [Serge Hallyn] Export filemap_checkpoint() (used for ext4)
>   - Introduce ckpt_collect_file() that also uses file->collect method
>   - Use ckpt_collect_file() instead of ckpt_obj_collect() for files
>   - Fix leak-detection issue in collect_mm() (test for first-time obj)
>   - Invoke set_close_on_exec() unconditionally on restart
>   - [Dan Smith] Export fill_fname() as ckpt_fill_fname()
>   - Interface to pass simple pointers as data with deferqueue
>   - [Dan Smith] Fix ckpt_obj_lookup_add() leak detection logic
>   - Replace EAGAIN with EBUSY where necessary
>   - Introduce CKPT_OBJ_VISITED in leak detection
>   - ckpt_obj_collect() returns objref for new objects, 0 otherwise
>   - Rename ckpt_obj_checkpointed() to ckpt_obj_visited()
>   - Introduce ckpt_obj_visit() to mark objects as visited
>   - Set the CHECKPOINTED flag on objects before calling checkpoint
>   - Introduce ckpt_obj_reserve()
>   - Change ref_drop() to accept a @lastref argument (for cleanup)
>   - Disallow multiple objects with same objref in restart
>   - Allow _ckpt_read_obj_type() to read header only (w/o payload)
>   - Fix leak of ckpt_ctx when restoring zombie tasks
>   - Fix race of prepare_descendant() with an ongoing fork()
>   - Track and report the first error if restart fails
>   - Tighten logic to protect against bogus pids in input
>   - [Matt Helsley] Improve debug output from ckpt_notify_error()
>   - [Nathan Lynch] fix compilation errors with CONFIG_COMPAT=y
>   - Detect error-headers in input data on restart, and abort.
>   - Standard format for checkpoint error strings (and documentation)
>   - [Dan Smith] Add an errno validation function
>   - Add ckpt_read_payload(): read a variable-length object (no header)
>   - Add ckpt_read_string(): same for strings (ensures null-terminated)
>   - Add ckpt_read_consume(): consumes next object without processing
>   - [John Dykstra] Fix no-dot-config-targets pattern in linux/Makefile
> 
> [2009-Jul-21] v17
>   - Introduce syscall clone_with_pids() to restore original pids
>   - Support threads and zombies
>   - Save/restore task->files
>   - Save/restore task->sighand
>   - Save/restore futex
>   - Save/restore credentials
>   - Introduce PF_RESTARTING to skip notifications on task exit
>   - restart(2) allow caller to ask to freeze tasks after restart
>   - restart(2) isn't idempotent: return -EINTR if interrupted
>   - Improve debugging output handling 
>   - Make multi-process restart logic more robust and complete
>   - Correctly select return value for restarting tasks on success
>   - Tighten ptrace test for checkpoint to PTRACE_MODE_ATTACH
>   - Use CHECKPOINTING state for frozen checkpointed tasks
>   - Fix compilation without CONFIG_CHECKPOINT
>   - Fix compilation with CONFIG_COMPAT
>   - Fix headers includes and exports
>   - Leak detection performed in two steps
>   - Detect "inverse" leaks of objects (dis)appearing unexpectedly
>   - Memory: save/restore mm->{flags,def_flags,saved_auxv}
>   - Memory: only collect sub-objects of mm once (leak detection)
>   - Files: validate f_mode after restore
>   - Namespaces: leak detection for nsproxy sub-components
>   - Namespaces: proper restart from namespace(s) without namespace(s)
>   - Save global constants in header instead of per-object
>   - IPC: replace sys_unshare() with create_ipc_ns()
>   - IPC: restore objects in suitable namespace
>   - IPC: correct behavior under !CONFIG_IPC_NS
>   - UTS: save/restore all fields
>   - UTS: replace sys_unshare() with create_uts_ns()
>   - X86_32: sanitize cpu, debug, and segment registers on restart
>   - cgroup_freezer: add CHECKPOINTING state to safeguard checkpoint
>   - cgroup_freezer: add interface to freeze a cgroup (given a task)
> 
> [2009-May-27] v16
>   - Privilege checks for IPC checkpoint
>   - Fix error string generation during checkpoint
>   - Use kzalloc for header allocation
>   - Restart blocks are arch-independent
>   - Redo pipe c/r using splice
>   - Fixes to s390 arch
>   - Remove powerpc arch (temporary)
>   - Explicitly restore ->nsproxy
>   - All objects in image are precedeed by 'struct ckpt_hdr'
>   - Fix leaks detection (and leaks)
>   - Reorder of patchset
>   - Misc bugs and compilation fixes
> 
> [2009-Apr-12] v15
>   - Minor fixes
> 
> [2009-Apr-28] v14
>   - Tested against kernel v2.6.30-rc3 on x86_32.
>   - Refactor files chekpoint to use f_ops (file operations)
>   - Refactor mm/vma to use vma_ops
>   - Explicitly handle VDSO vma (and require compat mode)
>   - Added code to c/r restat-blocks (restart timeout related syscalls)
>   - Added code to c/r namespaces: uts, ipc (with Dan Smith)
>   - Added code to c/r sysvipc (shm, msg, sem)
>   - Support for VM_CLONE shared memory
>   - Added resource leak detection for whole-container checkpoint
>   - Added sysctl gauge to allow unprivileged restart/checkpoint
>   - Improve and simplify the code and logic of shared objects
>   - Rework image format: shared objects appear prior to their use
>   - Merge checkpoint and restart functionality into same files
>   - Massive renaming of functions: prefix "ckpt_" for generics,
>     "checkpoint_" for checkpoint, and "restore_" for restart.
>   - Report checkpoint errors as a valid (string record) in the output
>   - Merged PPC architecture (by Nathan Lunch),
>   - Requires updates to userspace tools too.
>   - Misc nits and bug fixes
> 
> [2009-Mar-31] v14-rc2
>   - Change along Dave's suggestion to use f_ops->checkpoint() for files
>   - Merge patch simplifying Kconfig, with CONFIG_CHECKPOINT_SUPPORT
>   - Merge support for PPC arch (Nathan Lynch)
>   - Misc cleanups and fixes in response to comments
> 
> [2009-Mar-20] v14-rc1:
>   - The 'h.parent' field of 'struct cr_hdr' isn't used - discard
>   - Check whether calls to cr_hbuf_get() succeed or fail.
>   - Fixed of pipe c/r code
>   - Prevent deadlock by refusing c/r when a pipe inode == ctx->file inode
>   - Refuse non-self checkpoint if a task isn't frozen
>   - Use unsigned fields in checkpoint headers unless otherwise required
>   - Rename functions in files c/r to better reflect their role
>   - Add support for anonymous shared memory
>   - Merge support for s390 arch (Dan Smith, Serge Hallyn)
>     
> [2008-Dec-03] v13:
>   - Cleanups of 'struct cr_ctx' - remove unused fields
>   - Misc fixes for comments
>   
> [2008-Dec-17] v12:
>   - Fix re-alloc/reset of pgarr chain to correctly reuse buffers
>     (empty pgarr are saves in a separate pool chain)
>   - Add a couple of missed calls to cr_hbuf_put()
>   - cr_kwrite/cr_kread() again use vfs_read(), vfs_write() (safer)
>   - Split cr_write/cr_read() to two parts: _cr_write/read() helper
>   - Befriend with sparse: explicit conversion to 'void __user *'
>   - Redrefine 'pr_fmt' ind replace cr_debug() with pr_debug()
> 
> [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.
> 
>