691b4a4e7e
Any filesystem syscall, that needs to navigate to inode by it's absolute path performs successive lookup operations for each part of the path. Lookup operation includes access rights check. Usually but not always zdtm tests processes fall under 'other' access category. Also, usually directories don't have 'x' bit set for other. In case when bit 'x' is not set and user-ID and group-ID of a process relate it to 'other', test's will not succeed in performing these syscalls which are most of filesystem api, that has const char *path as part of it arguments (open, openat, mkdir, bind, etc). The observable behavior of that is that zdtm tests fail at file creation ops on one system and pass on the other. The above is not immediately clear to the developer by just looking at failed test's logs. Investigation of that is also not quick for a developer due to the complex structure of zdtm runtime where nested clones with NAMESPACE flags take place alongside with bind-mounts. As an additional note: 'get_current_dir_name' is documented as returning EACCESS in case when some part of the path lacks read/list permissions. But in fact it's not always so. Practice shows, that test processes can get false success on this operation only to fail on later call to something like mkdir/mknod/bind with a given path in arguments. 'get_cwd_check_perm' is a wrapper around 'get_current_dir_name'. It also checks for permissions on the given filepath and logs the error. This directs the developer towards the right investigation path or even eliminates the need for investigation completely. Signed-off-by: Valeriy Vdovin <valeriy.vdovin@virtuozzo.com> |
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| compel | ||
| contrib | ||
| coredump | ||
| crit | ||
| criu | ||
| Documentation | ||
| images | ||
| include/common | ||
| lib | ||
| scripts | ||
| soccr | ||
| test | ||
| .gitignore | ||
| .mailmap | ||
| .travis.yml | ||
| COPYING | ||
| CREDITS | ||
| INSTALL.md | ||
| MAINTAINERS | ||
| MAINTAINERS_GUIDE.md | ||
| Makefile | ||
| Makefile.compel | ||
| Makefile.config | ||
| Makefile.install | ||
| Makefile.versions | ||
| README.md | ||
CRIU -- A project to implement checkpoint/restore functionality for Linux
CRIU (stands for Checkpoint and Restore in Userspace) is a utility to checkpoint/restore Linux tasks.
Using this tool, you can freeze a running application (or part of it) and checkpoint it to a hard drive as a collection of files. You can then use the files to restore and run the application from the point it was frozen at. The distinctive feature of the CRIU project is that it is mainly implemented in user space. There are some more projects doing C/R for Linux, and so far CRIU appears to be the most feature-rich and up-to-date with the kernel.
The project started as the way to do live migration for OpenVZ Linux containers, but later grew to more sophisticated and flexible tool. It is currently used by (integrated into) OpenVZ, LXC/LXD, Docker, and other software, project gets tremendous help from the community, and its packages are included into many Linux distributions.
The project home is at http://criu.org. This wiki contains all the knowledge base for CRIU we have. Pages worth starting with are:
- Installation instructions
- A simple example of usage
- Examples of more advanced usage
- Troubleshooting can be hard, some help can be found here, here and here
Checkpoint and restore of simple loop process
Advanced features
As main usage for CRIU is live migration, there's a library for it called P.Haul. Also the project exposes two cool core features as standalone libraries. These are libcompel for parasite code injection and libsoccr for TCP connections checkpoint-restore.
Live migration
True live migration using CRIU is possible, but doing all the steps by hands might be complicated. The phaul sub-project provides a Go library that encapsulates most of the complexity. This library and the Go bindings for CRIU are stored in the go-criu repository.
Parasite code injection
In order to get state of the running process CRIU needs to make this process execute some code, that would fetch the required information. To make this happen without killing the application itself, CRIU uses the parasite code injection technique, which is also available as a standalone library called libcompel.
TCP sockets checkpoint-restore
One of the CRIU features is the ability to save and restore state of a TCP socket without breaking the connection. This functionality is considered to be useful by itself, and we have it available as the libsoccr library.
How to contribute
CRIU project is (almost) the never-ending story, because we have to always keep up with the Linux kernel supporting checkpoint and restore for all the features it provides. Thus we're looking for contributors of all kinds -- feedback, bug reports, testing, coding, writing, etc. Here are some useful hints to get involved.
- We have both -- very simple and more sophisticated coding tasks;
- CRIU does need extensive testing;
- Documentation is always hard, we have some information that is to be extracted from people's heads into wiki pages as well as some texts that all need to be converted into useful articles;
- Feedback is expected on the github issues page and on the mailing list;
- We accept github pull requests and this is the preferred way to contribute to CRIU. If you prefer to send patches by email, you are welcome to send them to the devel list;
- Spread the word about CRIU in social networks;
- If you're giving a talk about CRIU -- let us know, we'll mention it on the wiki main page;
Licence
The project is licensed under GPLv2 (though files sitting in the lib/ directory are LGPLv2.1).