7d602fc87e
When a process has inotify (or fanotify) watches on files inside an
overlayfs mount, criu dump fails because open_by_handle_at() does not
work for overlay file handles (type OVL_FILEID_V1 = 0xf8). The dump
log shows:
fsnotify: wd 0x000001 s_dev 0x00002d i_ino 0x101ad2 mask 0x00033a
fsnotify: [fhandle] bytes 0x000020 type 0x0000f8 ...
fsnotify: Handle 0x2d:0x101ad2 cannot be opened
Error (criu/fsnotify.c:284): fsnotify: Can't dump that handle
To reproduce manually:
mkdir -p /tmp/{lower,upper,work,merged}
touch /tmp/lower/testfile
mount -t overlay overlay \
-o lowerdir=/tmp/lower,upperdir=/tmp/upper,workdir=/tmp/work \
/tmp/merged
inotifywait -m /tmp/merged/testfile &
PID=$!
criu dump -t $PID -D /tmp/imgs --shell-job --ext-unix-sk
alloc_openable() iterates mounts matching s_dev and tries
open_by_handle_at() for each one. Overlay file handles use the
private OVL_FILEID_V1 type which open_by_handle_at() does not
support, so the call always fails and the dump aborts.
Add a fallback for overlay mounts: when open_by_handle_at() fails
and the mount is identified as FSTYPE__OVERLAYFS, walk the overlay
mount's directory tree with opendir/readdir/fstatat to find the
file matching the (s_dev, i_ino) pair from the handle. Store the
discovered absolute path in f_handle->path so that get_mark_path()
uses the path-based openat() strategy on restore, which works on
overlay mounts.
The fallback only triggers when open_by_handle_at() fails AND the
mount type is FSTYPE__OVERLAYFS, so there is no impact on other
filesystems.
Assisted-by: Claude Code (claude-opus-4-6):default
Signed-off-by: Adrian Reber <areber@redhat.com>
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|---|---|---|
| .circleci | ||
| .github | ||
| compel | ||
| contrib | ||
| coredump | ||
| crit | ||
| criu | ||
| Documentation | ||
| images | ||
| include | ||
| lib | ||
| plugins | ||
| scripts | ||
| soccr | ||
| test | ||
| .clang-format | ||
| .codespellrc | ||
| .gitignore | ||
| .lgtm.yml | ||
| .mailmap | ||
| CLAUDE.md | ||
| CONTRIBUTING.md | ||
| COPYING | ||
| CREDITS | ||
| docs | ||
| flake.lock | ||
| flake.nix | ||
| GEMINI.md | ||
| 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.
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. Please refer to CONTRIBUTING.md if you would like to get involved.
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.
Licence
The project is licensed under GPLv2 (though files sitting in the lib/ directory are LGPLv2.1).
All files in the images/ directory are licensed under the Expat license (so-called MIT). See the images/LICENSE file.