Checklist crnext

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A feature being unsupported for checkpoint/restart could mean two things.  It
could mean that checkpoint on an application using the feature will fail.  For
instance, if an application has an open fd on an unsupported device or on a file
of an unsupported fs, then checkpoint will fail with an informative error message.
That is ok.
It could also mean that checkpoint will 'succeed', but restart will fail.  Worse,
it could mean that restart will 'succeed', but the application will misbehave after
restart.  For instance, we currently do not address mounts.  So if an application has
done 'mount(FILE1, FILE2, NULL, MS_BIND, 0)' before being checkpointed, then after
restart FILE1 may no longer be bind-mounted onto FILE2.
'''What is implemented'''
'''What is implemented'''

Revision as of 16:56, 21 December 2009

What is implemented

* open regular files and directories:
  * ext2, ext3, ext4
* /dev/null, zero, random, urandom
* epoll fd's
* event fd's
* timer fd's
* signal fd's
* unix sockets
* ipv4 sockets (except time-wait sockets)
* SYSV IPC (message queues, semaphores, and shared memory)
  * except semaphore undo
* Unix98 ptys
* futexes
* process ids
* credentials (userid, group, and POSIX capabilities)
* Smack LSM labels
* pipes
* signals
* multiple processes, threads
* nested namespaces of:
  * user
  * IPC
  * UTS (hostname)
  * IPC
  * (nested pid namespaces only require userspace support)

What is NOT implemented (please make each a link to a page describing issues, a design for solving, how we will detect it to refuse checkpoint if we will not support it, and "how ugly it will make the kernel". The table summarizes these details. )

Not Implemented Refuses to Checkpoint
Anticipated Solution Impact
mounts Yes
network devices, time-wait inet sockets Yes
unlinked files and directories Yes
inotify Yes Probably gross due to watches attaching to inodes
FUSE Yes Clean but requires per-FUSE-filesystem support
network and distributed filesystems Yes
SYSV IPC: semaphore undo No Small, clean
netlink Yes
new, expiremental, and/or
infrastructure-oriented network protocols
file locks Yes
file leases Yes
fowner+sigio Yes
ptraced tasks Yes
time namespace N/A
restart of 64-bit task from
32-bit task and vice versa
inet6 sockets
(previously supported, just need
to add it back in. minor)
Hardware devices
other than those mentioned above.
Includes mmap, /dev/foo, Infiniband devices
System-specific files in sysfs
(things like UUID files)
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