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
* 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 and SELinux LSM labels * pipes * FIFOs * signals * multiple processes, threads * nested namespaces of: * user * IPC * UTS (hostname) * IPC * (nested pid namespaces only require userspace support)
* x86-32, x86-64 * PowerPC * s390x
Click here for information about architecture specific.
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 namespaces||Yes||Clean (the dirty work will be in mounts themselves)|
|time-wait inet sockets||No|
|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||Clean, low priority.|
| new, expiremental, and/or
infrastructure-oriented network protocols
|file locks||Yes||Trivial and clean, planned for v20.|
|file leases||Yes||Trivial and clean, planned for v20.|
|fowner+sigio||Yes||Trivial and clean, planned for v20.|
| restart of 64-bit task from
32-bit task and vice versa
|Yes||Probably in userspace|
|inet6 sockets||Yes|| Previously supported, just need |
to add it back in. minor.
| Hardware devices
other than those mentioned above.
Includes mmap, /dev/foo, Infiniband devices
|Yes (mostly)||One idea|
| System-specific files in sysfs
(things like UUID files)