Difference between revisions of "Google Summer of Code Ideas"

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This page contains project ideas for upcoming Google Summer of Code.
 
This page contains project ideas for upcoming Google Summer of Code.
  
−
== Suggested ideas ==
+
== Contacts ==
  
 +
Please contact the respective mentor for the idea you are interested in. For general questions feel free to send an email to the [mailto:criu@openvz.org mailing list] or write in [https://gitter.im/save-restore/criu gitter].
  
−
=== Post-copy for shared memory and hugetlbfs ===
+
== Project ideas ==
−
 
−
'''Summary:''' extend post-copy memory restore and migration to support shared memory and hugetlbfs.
 
  
−
CRIU relies on [[Userfaultfd]] mechanism in the Linux kernel to implement the demand paging in userspace and allow post-copy memory (or lazy) [[Lazy_migration|migration]]. However, currently this support is limited to anonymous private memory mappings, although kernel also supports shared memory areas and hugetlbfs backed memory.
+
=== Add support for memory compression ===
−
 
 
−
The shared memory support for lazy migration can be added to CRIU without kernel modifications, while proper handling of hugetlbfs would require userfaultfd callbacks for [http://man7.org/linux/man-pages/man2/fallocate.2.html fallocate(PUNCH_HOLE)] and [http://man7.org/linux/man-pages/man2/madvise.2.html madvise(MADV_REMOVE)] system calls.
 
 
   
 
   
−
'''Links:'''
+
'''Summary:''' Support compression for page images
−
* [https://www.kernel.org/doc/html/latest/admin-guide/mm/userfaultfd.html Userfaultfd]
 
−
* [https://www.kernel.org/doc/html/latest/admin-guide/mm/hugetlbpage.html hugetlbfs]
 
−
'''Details:'''
 
−
* Skill level: most probably advanced?
 
−
* Language: C
 
−
* Mentor: Mike Rapoport <rppt@linux.ibm.com> / Andrey Vagin <avagin@gmail.com>
 
−
* Suggested by: Mike Rapoport <rppt@linux.ibm.com>
 
−
 
 
−
=== Optimize logging engine ===
 
 
   
 
   
−
'''Summary:''' CRIU puts a lots of logs when doing its job. Logging is done with simple fprintf function. They are typically useless, but ''if'' some operation fails -- the logs are the only way to find what was the reason for failure.
+
We would like to support memory page files compression
−
 
+
in CRIU using one of the fastest algorithms (it's matter
−
At the same time the printf family of functions is known to take some time to work -- they need to scan the format string for %-s and then convert the arguments into strings. If comparing criu dump with and without logs the time difference is notable (15%-20%), so speeding the logs up will help improve criu performance.
+
of discussion which one to choose!).
  
−
One of the solutions to the problem might be binary logging. The problem with binary logs is the amount of efforts to convert existing logs to binary form. Preferably, the switch to binary logging either keeps existing log() calls intact, either has some automatics to convert them.
+
This task does not require any Linux kernel modifications
−
 
+
and scope is limited to CRIU itself. At the same time it's
−
The option to keep log() calls intact might be in pre-compilation pass of the sources. In this pass each <code>log(fmt, ...)</code> call gets translated into a call to a binary log function that saves <code>fmt</code> identifier copies all the args ''as is'' into the log file. The binary log decode utility, required in this case, should then find the fmt string by its ID in the log file and print the resulting message.
+
complex enough as we need to touch memory dump/restore codepath
−
 
+
in CRIU and also handle many corner cases like page-server and stuff.
−
'''Links:'''
 
−
* [[Better logging]]
 
 
   
 
   
 
'''Details:'''
 
'''Details:'''
 
* Skill level: intermediate
 
* Skill level: intermediate
−
* Language: C, though decoder/preprocessor can be in any language
+
* Language: C
−
* Mentor: Andrei Vagin <avagin@gmail.com> / Pavel Emelyanov <xemul@openvz.org>
+
* Expected size: 350 hours
 
* Suggested by: Andrei Vagin <avagin@gmail.com>
 
* Suggested by: Andrei Vagin <avagin@gmail.com>
 +
* Mentors: Alexander Mikhalitsyn <alexander@mihalicyn.com>, Andrei Vagin <avagin@gmail.com>
  
 
=== Add support for checkpoint/restore of CORK-ed UDP socket ===
 
=== Add support for checkpoint/restore of CORK-ed UDP socket ===
Line 62: Line 49:
 
'''Links:'''
 
'''Links:'''
 
* https://github.com/checkpoint-restore/criu/issues/409
 
* https://github.com/checkpoint-restore/criu/issues/409
 +
* https://github.com/criupatchwork/criu/commit/a532312
 
* [[Sockets]], [[TCP connection]]
 
* [[Sockets]], [[TCP connection]]
 
* [[https://groups.google.com/forum/#!topic/comp.os.linux.networking/Uz8PYiTCZSg UDP cork explained]]
 
* [[https://groups.google.com/forum/#!topic/comp.os.linux.networking/Uz8PYiTCZSg UDP cork explained]]
Line 68: Line 56:
 
* Skill level: intermediate (+linux kernel)
 
* Skill level: intermediate (+linux kernel)
 
* Language: C
 
* Language: C
−
* Mentor: Pavel Emelianov <xemul@virtuozzo.com>
+
* Expected size: 350 hours
−
* Suggested by: Pavel Emelianov <xemul@virtuozzo.com>
+
* Mentors: Alexander Mikhalitsyn <alexander@mihalicyn.com>, Pavel Tikhomirov <ptikhomirov@virtuozzo.com>, Andrei Vagin <avagin@gmail.com>
 +
 
 +
=== Add support for pidfd file descriptors ===
 +
 
 +
'''Summary:''' Support C/R of pidfd descriptors
 +
 
 +
There is pidfd_open syscall which allows opening
 +
a special PID file descriptor. A user can send a signal to
 +
the process (pidfd_send_signal syscall), wait for the process
 +
(poll() on pidfd).
 +
 
 +
At the moment CRIU can't dump processes that have pidfd's opened.
 +
 
 +
'''Links:'''
 +
* https://lwn.net/Articles/801319/
 +
* https://lwn.net/Articles/794707/
 +
* https://github.com/torvalds/linux/blob/v5.16/kernel/fork.c#L1877
 +
 +
'''Details:'''
 +
* Skill level: intermediate
 +
* Language: C
 +
* Expected size: 350 hours
 +
* Mentors: Alexander Mikhalitsyn <alexander@mihalicyn.com>, Christian Brauner <christian@brauner.io>
 +
* Suggested by: Alexander Mikhalitsyn <alexander@mihalicyn.com>
 +
 
 +
=== Use eBPF to lock and unlock the network ===
 +
 +
'''Summary:''' Use eBPF instead of external iptables-restore tool for network lock and unlock.
 +
 
 +
During checkpointing and restoring CRIU locks the network to make sure no network packets are accepted by the network stack during the time the process is checkpointed. Currently CRIU calls out to iptables-restore to create and delete the corresponding iptables rules. Another approach which avoids calling out to the external binary iptables-restore would be to directly inject eBPF rules. There have been reports from users that iptables-restore fails in some way and eBPF could avoid this external dependency.
 +
 
 +
'''Links:'''
 +
* https://www.criu.org/TCP_connection#Checkpoint_and_restore_TCP_connection
 +
* https://github.com/systemd/systemd/blob/master/src/core/bpf-firewall.c
 +
* https://blog.zeyady.com/2021-08-16/gsoc-criu
 +
 
 +
'''Details:'''
 +
* Skill level: intermediate
 +
* Language: C
 +
* Expected size: 350 hours
 +
* Mentors: Radostin Stoyanov <rstoyanov@fedoraproject.org>, Prajwal S N <prajwalnadig21@gmail.com>
 +
* Suggested by: Adrian Reber <areber@redhat.com>
 +
 
 +
=== Files on detached mounts ===
 +
 
 +
'''Summary:''' Initial support of open files on "detached" mounts
 +
 
 +
When criu dumps a process with an open fd on a file, it gets the mount identifier (mnt_id) via /proc/<pid>/fdinfo/<fd>, so that criu knows from which exact mount the file was initially opened. This way criu can restore this fd by opening the same exact file from topologically the same mount in restored mount tree.
 +
 
 +
Restoring fd from the right mount can be important in different cases, for instance if the process would later want to resolve paths relative to the fd, and obviously resolving from the same file on different mount can lead to different resolved paths, or if the process wants to check path to the file via /proc/<pid>/fd/<fd>.
 +
 
 +
But we have a problem finding on which mount we need to reopen the file at restore if we only know mnt_id but can't find this mnt_id in /proc/<pid>/mountinfo.
 +
 
 +
Mountinfo file shows the mount tree topology of current mntns: parent - child relations, sharing group information, mountpoint and fs root information. And if we don't see mnt_id in it we don't know anything about this mount.
 +
 
 +
This can happen in two cases
 +
 
 +
* 1) external mount or file - if file was opened from e.g. host it's mount would not be visible in container mountinfo
 +
* 2) mount was lazily unmounted
 +
 
 +
In case of 1) we have criu options to help criu handle external dependencies.
 +
 
 +
In case of 2) or no options provided criu can't resolve mnt_id in mountinfo and criu fails.
 +
 
 +
'''Solution:'''
 +
We can handle 2) with: resolving major/minor via fstat, using name_to_handle_at and open_by_handle_at to open same file on any other available mount from same superblock (same major/minor) in container. Now we have fd2 of the same file as fd, but on existing mount we can dump it as usual instead, and mark it as "detached" in image, now criu on restore knows where to find this file, but instead of just opening fd2 from actually restored mount, we create a temporary bindmount which is lazy unmounted just after open making the file appear as a file on detached mount.
 +
 
 +
Known problems with this approach:
 +
 
 +
* Stat on btrfs gives wrong major/minor
 +
* file handles does not work everywhere
 +
* file handles can return fd2 on deleted file or on other hardlink, this needs special handling.
 +
 
 +
Additionally (optional part):
 +
We can export real major/minor in fdinfo (kernel).
 +
We can think of new kernel interface to get mount's major/minor and root (shift from fsroot) for detached mounts, if we have it we don't need file handle hack to find file on other mount (see fsinfo or getvalues kernel patches in LKML, can we add this info there?).
 +
 
 +
'''Details:'''
 +
* Skill level: intermediate
 +
* Language: C
 +
* Expected size: 350 hours
 +
* Mentor: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
 +
* Suggested by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
 +
 
 +
=== Checkpointing of POSIX message queues ===
 +
 
 +
'''Summary:''' Add support for checkpoint/restore of POSIX message queues
 +
 
 +
POSIX message queues are a widely used inter-process communication mechanism. Message queues are implemented as files on a virtual filesystem (mqueue), where a file descriptor (message queue descriptor) is used to perform operations such as sending or receiving messages. To support checkpoint/restore of POSIX message queues, we need a kernel interface (similar to [https://github.com/checkpoint-restore/criu/commit/8ce9e947051e43430eb2ff06b96dddeba467b4fd MSG_PEEK]) that would enable the retrieval of messages from a queue without removing them. This project aims to implement such an interface that allows retrieving all messages and their priorities from a POSIX message queue.
 +
 
 +
'''Links:'''
 +
* https://github.com/checkpoint-restore/criu/issues/2285
 +
* https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/ipc/mqueue.c
 +
* https://www.man7.org/tlpi/download/TLPI-52-POSIX_Message_Queues.pdf
 +
 
 +
'''Details:'''
 +
* Skill level: intermediate
 +
* Language: C
 +
* Expected size: 350 hours
 +
* Mentors: Radostin Stoyanov <rstoyanov@fedoraproject.org>, Pavel Tikhomirov <ptikhomirov@virtuozzo.com>, Prajwal S N <prajwalnadig21@gmail.com>
 +
* Suggested by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
 +
 
 +
=== Kubernetes operator for managing container checkpoints ===
 +
 
 +
'''Summary:''' Develop a Kubernetes operator that automates the management of container checkpoints
 +
 
 +
Container checkpointing has recently been introduced as an alpha feature in Kubernetes.
 +
To enable this feature, the kubelet API was extended with an endpoint that enables the
 +
creation of checkpoints for individual containers. By default, all container checkpoints
 +
are stored as tar archives in <code>/var/lib/kubelet/checkpoints</code> using the following
 +
file name format: <code>checkpoint-<pod-name>_<namespace-name>-<container-name>-<timestamp>.tar</code>.
 +
However, the current implementation does not provide a mechanism for limiting the number
 +
of checkpoints, which may lead to filling up all existing disk space. This project aims to
 +
develop a Kubernetes operator that automates the management of checkpoints and provides
 +
a garbage collection mechanism to discard obsolete checkpoints.
 +
 
 +
'''Links:'''
 +
* https://github.com/checkpoint-restore/checkpoint-restore-operator
 +
* https://kubernetes.io/docs/reference/node/kubelet-checkpoint-api/
 +
* https://kubernetes.io/blog/2022/12/05/forensic-container-checkpointing-alpha/
 +
* https://kubernetes.io/blog/2023/03/10/forensic-container-analysis/
 +
* https://github.com/kubernetes/kubernetes/pull/115888
 +
* https://github.com/kubernetes/enhancements/issues/2008
 +
 
 +
'''Details:'''
 +
* Skill level: intermediate
 +
* Language: Go
 +
* Expected size: 350 hours
 +
* Mentors: Adrian Reber <areber@redhat.com>, Radostin Stoyanov <rstoyanov@fedoraproject.org>, Prajwal S N <prajwalnadig21@gmail.com>
 +
* Suggested by: Adrian Reber
 +
 
 +
== Suspended project ideas ==
 +
 
 +
Listed here are tasks that seem suitable for GSoC, but currently do not have anybody to mentor it.
 +
 
 +
=== Optimize logging engine ===
 +
 +
'''Summary:''' CRIU puts a lots of logs when doing its job. Logging is done with simple fprintf function. They are typically useless, but ''if'' some operation fails -- the logs are the only way to find what was the reason for failure.
 +
 
 +
At the same time the printf family of functions is known to take some time to work -- they need to scan the format string for %-s and then convert the arguments into strings. If comparing criu dump with and without logs the time difference is notable (15%-20%), so speeding the logs up will help improve criu performance.
 +
 
 +
One of the solutions to the problem might be binary logging. The problem with binary logs is the amount of efforts to convert existing logs to binary form. Preferably, the switch to binary logging either keeps existing log() calls intact, either has some automatics to convert them.
 +
 
 +
The option to keep log() calls intact might be in pre-compilation pass of the sources. In this pass each <code>log(fmt, ...)</code> call gets translated into a call to a binary log function that saves <code>fmt</code> identifier copies all the args ''as is'' into the log file. The binary log decode utility, required in this case, should then find the fmt string by its ID in the log file and print the resulting message.
 +
 
 +
'''Links:'''
 +
* [[Better logging]]
 +
 +
'''Details:'''
 +
* Skill level: intermediate
 +
* Language: C, though decoder/preprocessor can be in any language
 +
* Expected size: 350 hours
 +
* Suggested by: Andrei Vagin
 +
* Mentors: Alexander Mikhalitsyn <alexander@mihalicyn.com>
 +
 
 +
=== IOUring support ===
 +
The io_uring Asynchronous I/O (AIO) framework is a new Linux I/O interface, first introduced in upstream Linux kernel version 5.1 (March 2019). It provides a low-latency and feature-rich interface for applications that require AIO functionality.
 +
 
 +
'''Links:'''
 +
* https://blogs.oracle.com/linux/an-introduction-to-the-io_uring-asynchronous-io-framework
 +
* https://github.com/axboe/liburing
 +
 
 +
'''Details:'''
 +
* Skill level: expert (+linux kernel)
 +
* Expected size: 350 hours
 +
 
 +
=== Add support for SPFS ===
 +
 +
'''Summary:''' The SPFS is a special filesystem that allows checkpoint and restore of such things as NFS and FUSE
 +
 
 +
NFS support is already implemented in Virtuozzo CRIU, but it's very beneficial to port it to mainline CRIU. The importaint part of it is the need to implement the integration of Stub-Proxy File System (SPFS) with LXC/yet_another_containers_environment.
 +
 
 +
'''Links'''
 +
* https://github.com/checkpoint-restore/criu/issues/60
 +
* https://github.com/checkpoint-restore/criu/issues/53
 +
* https://github.com/skinsbursky/spfs
 +
* https://patchwork.criu.org/series/137/
 +
 
 +
'''Details:'''
 +
* Skill level: expert
 +
* Language: C
 +
* Mentor: Alexander Mikhalitsyn <alexander@mihalicyn.com>
 +
* Suggested by: Alexander Mikhalitsyn <alexander@mihalicyn.com>
 +
 
  
 
=== Anonymise image files ===
 
=== Anonymise image files ===
Line 97: Line 268:
 
* Skill level: beginner
 
* Skill level: beginner
 
* Language: Python
 
* Language: Python
−
* Mentor: Pavel Emelianov <xemul@virtuozzo.com>
 
−
* Suggested by: Pavel Emelianov <xemul@virtuozzo.com>
 
−
 
−
=== Porting crit functionalities in GO ===
 
−
 
−
'''Summary:''' Implement image view and manipulation in Go
 
−
 
−
CRIU's checkpoint images are stored on disk using protobuf. For easier analysis of checkpoint files CRIU has a tool called [[CRIT|CRiu Image Tool (CRIT)]]. It can display/decode CRIU image files from binary protobuf to JSON as well as encode JSON files back to the binary format. With closer integration of CRIU in container runtimes it becomes important to be able to view the CRIU output files. Either for manipulation before restoring or for reading checkpoint statistics (memory pages written to disk, memory pages skipped, process downtime).
 
−
 
−
Currently CRIT is implemented in Python, for easier integration in other Go projects it is important to have image manipulation and analysis available from GO. This means we need a Go based library to read/modify/write/encode/decode CRIU's image files. Based on this library a Go based implementation of CRIT would be useful.
 
−
 
−
'''Links:'''
 
−
* [[CRIT]]
 
−
* Possible use case see LXD: https://github.com/lxc/lxd/blob/cb55b1c5a484a43e0c21c6ae8c4a2e30b4d45be3/lxd/migrate_container.go#L179
 
−
* https://github.com/lxc/lxd/pull/4072
 
−
* https://github.com/checkpoint-restore/go-criu/blob/master/phaul/stats.go
 
−
 
−
'''Details:'''
 
−
* Skill level: beginner
 
−
* Language: Go
 
−
* Mentor: Adrian Reber <areber@redhat.com>
 
−
* Suggested by: Adrian Reber <areber@redhat.com>
 
  
−
=== Memory changes tracking with userfaultfd-WP ===
 
−
 
−
'''Summary:''' add ability to track memory changes of the snapshotted processes using userfaultfd-WP
 
−
 
−
Currently CRIU uses [[Memory_changes_tracking|Soft-dirty]] mechanism in Linux kernel to track memory changes.
 
−
This mechanism can be complemented (or even completely replaced) with recently proposed write protection support for
 
−
userfaultfd (userfaultfd-WP).
 
  
−
Userfault allows implementation of paging in userspace. It allows an application to receive notifications about page faults and provide the desired memory contents for the faulting pages. In the current upstream kernels only missing page faults are supported, but there is an ongoing work to allow notifications for write faults as well. Using such notifications it would be possible to precisely track memory changes during pre-dump iterations. This approach may prove to be more efficient than soft-dirty.
 
−
 
−
'''Links:'''
 
−
* [https://www.kernel.org/doc/html/latest/admin-guide/mm/userfaultfd.html Userfaultfd]
 
−
* [https://github.com/xzpeter/linux/tree/uffd-wp-merged Userfaultfd-WP]
 
−
* [https://www.kernel.org/doc/html/latest/admin-guide/mm/soft-dirty.html?highlight=soft%20dirty Soft-Dirty]
 
−
* https://lwn.net/Articles/777258/
 
−
 
−
'''Details:'''
 
−
* Skill level: most probably advanced?
 
−
* Language: C
 
−
* Mentor: Mike Rapoport <rppt@linux.ibm.com>
 
−
* Suggested by: Mike Rapoport <rppt@linux.ibm.com>
 
−
 
−
=== Use eBPF to lock and unlock the network ===
 
−
 
−
'''Summary:''' Use ePBF instead of external iptables-restore tool for network lock and unlock.
 
−
 
−
During checkpointing and restoring CRIU locks the network to make sure no network packets are accepted by the network stack during the time the process is checkpointed. Currently CRIU calls out to iptables-restore to create and delete the corresponding iptables rules. Another approach which avoids calling out to the external binary iptables-restore would be to directly inject eBPF rules. There have been reports from users that iptables-restore fails in some way and eBPF could avoid this external dependency.
 
−
 
−
'''Links:'''
 
−
* https://www.criu.org/TCP_connection#Checkpoint_and_restore_TCP_connection
 
−
* https://github.com/systemd/systemd/blob/master/src/core/bpf-firewall.c
 
−
 
−
'''Details:'''
 
−
* Skill level: intermediate
 
−
* Language: C
 
−
* Mentor: Adrian Reber <areber@redhat.com>
 
−
* Suggested by: Adrian Reber <areber@redhat.com>
 
  
 
[[Category:GSoC]]
 
[[Category:GSoC]]
 
[[Category:Development]]
 
[[Category:Development]]

Latest revision as of 03:11, 26 March 2024

Google Summer of Code (GSoC) is a global program that offers post-secondary students an opportunity to be paid for contributing to an open source project over a three month period.

This page contains project ideas for upcoming Google Summer of Code.

Contacts[edit]

Please contact the respective mentor for the idea you are interested in. For general questions feel free to send an email to the mailing list or write in gitter.

Project ideas[edit]

Add support for memory compression[edit]

Summary: Support compression for page images

We would like to support memory page files compression in CRIU using one of the fastest algorithms (it's matter of discussion which one to choose!).

This task does not require any Linux kernel modifications and scope is limited to CRIU itself. At the same time it's complex enough as we need to touch memory dump/restore codepath in CRIU and also handle many corner cases like page-server and stuff.

Details:

  • Skill level: intermediate
  • Language: C
  • Expected size: 350 hours
  • Suggested by: Andrei Vagin <avagin@gmail.com>
  • Mentors: Alexander Mikhalitsyn <alexander@mihalicyn.com>, Andrei Vagin <avagin@gmail.com>

Add support for checkpoint/restore of CORK-ed UDP socket[edit]

Summary: Support C/R of corked UDP socket

There's UDP_CORK option for sockets. As man page says: 

    If this option is enabled, then all data output on this socket
    is accumulated into a single datagram that is transmitted when
    the option is disabled.  This option should not be used in
    code intended to be portable.

Currently criu refuses to dump this case, so it's effectively a bug. Supporting this will need extending the kernel API to allow criu read back the write queue of the socket (see how it's done for TCP sockets, for example). Then the queue is written into the image and is restored into the socket (with the CORK bit set too).

Links:

Details:

  • Skill level: intermediate (+linux kernel)
  • Language: C
  • Expected size: 350 hours
  • Mentors: Alexander Mikhalitsyn <alexander@mihalicyn.com>, Pavel Tikhomirov <ptikhomirov@virtuozzo.com>, Andrei Vagin <avagin@gmail.com>

Add support for pidfd file descriptors[edit]

Summary: Support C/R of pidfd descriptors

There is pidfd_open syscall which allows opening a special PID file descriptor. A user can send a signal to the process (pidfd_send_signal syscall), wait for the process (poll() on pidfd).

At the moment CRIU can't dump processes that have pidfd's opened.

Links:

Details:

  • Skill level: intermediate
  • Language: C
  • Expected size: 350 hours
  • Mentors: Alexander Mikhalitsyn <alexander@mihalicyn.com>, Christian Brauner <christian@brauner.io>
  • Suggested by: Alexander Mikhalitsyn <alexander@mihalicyn.com>

Use eBPF to lock and unlock the network[edit]

Summary: Use eBPF instead of external iptables-restore tool for network lock and unlock.

During checkpointing and restoring CRIU locks the network to make sure no network packets are accepted by the network stack during the time the process is checkpointed. Currently CRIU calls out to iptables-restore to create and delete the corresponding iptables rules. Another approach which avoids calling out to the external binary iptables-restore would be to directly inject eBPF rules. There have been reports from users that iptables-restore fails in some way and eBPF could avoid this external dependency.

Links:

Details:

  • Skill level: intermediate
  • Language: C
  • Expected size: 350 hours
  • Mentors: Radostin Stoyanov <rstoyanov@fedoraproject.org>, Prajwal S N <prajwalnadig21@gmail.com>
  • Suggested by: Adrian Reber <areber@redhat.com>

Files on detached mounts[edit]

Summary: Initial support of open files on "detached" mounts

When criu dumps a process with an open fd on a file, it gets the mount identifier (mnt_id) via /proc/<pid>/fdinfo/<fd>, so that criu knows from which exact mount the file was initially opened. This way criu can restore this fd by opening the same exact file from topologically the same mount in restored mount tree.

Restoring fd from the right mount can be important in different cases, for instance if the process would later want to resolve paths relative to the fd, and obviously resolving from the same file on different mount can lead to different resolved paths, or if the process wants to check path to the file via /proc/<pid>/fd/<fd>.

But we have a problem finding on which mount we need to reopen the file at restore if we only know mnt_id but can't find this mnt_id in /proc/<pid>/mountinfo.

Mountinfo file shows the mount tree topology of current mntns: parent - child relations, sharing group information, mountpoint and fs root information. And if we don't see mnt_id in it we don't know anything about this mount.

This can happen in two cases

  • 1) external mount or file - if file was opened from e.g. host it's mount would not be visible in container mountinfo
  • 2) mount was lazily unmounted

In case of 1) we have criu options to help criu handle external dependencies.

In case of 2) or no options provided criu can't resolve mnt_id in mountinfo and criu fails.

Solution: We can handle 2) with: resolving major/minor via fstat, using name_to_handle_at and open_by_handle_at to open same file on any other available mount from same superblock (same major/minor) in container. Now we have fd2 of the same file as fd, but on existing mount we can dump it as usual instead, and mark it as "detached" in image, now criu on restore knows where to find this file, but instead of just opening fd2 from actually restored mount, we create a temporary bindmount which is lazy unmounted just after open making the file appear as a file on detached mount.

Known problems with this approach:

  • Stat on btrfs gives wrong major/minor
  • file handles does not work everywhere
  • file handles can return fd2 on deleted file or on other hardlink, this needs special handling.

Additionally (optional part): We can export real major/minor in fdinfo (kernel). We can think of new kernel interface to get mount's major/minor and root (shift from fsroot) for detached mounts, if we have it we don't need file handle hack to find file on other mount (see fsinfo or getvalues kernel patches in LKML, can we add this info there?).

Details:

  • Skill level: intermediate
  • Language: C
  • Expected size: 350 hours
  • Mentor: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>
  • Suggested by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>

Checkpointing of POSIX message queues[edit]

Summary: Add support for checkpoint/restore of POSIX message queues

POSIX message queues are a widely used inter-process communication mechanism. Message queues are implemented as files on a virtual filesystem (mqueue), where a file descriptor (message queue descriptor) is used to perform operations such as sending or receiving messages. To support checkpoint/restore of POSIX message queues, we need a kernel interface (similar to MSG_PEEK) that would enable the retrieval of messages from a queue without removing them. This project aims to implement such an interface that allows retrieving all messages and their priorities from a POSIX message queue.

Links:

Details:

  • Skill level: intermediate
  • Language: C
  • Expected size: 350 hours
  • Mentors: Radostin Stoyanov <rstoyanov@fedoraproject.org>, Pavel Tikhomirov <ptikhomirov@virtuozzo.com>, Prajwal S N <prajwalnadig21@gmail.com>
  • Suggested by: Pavel Tikhomirov <ptikhomirov@virtuozzo.com>

Kubernetes operator for managing container checkpoints[edit]

Summary: Develop a Kubernetes operator that automates the management of container checkpoints

Container checkpointing has recently been introduced as an alpha feature in Kubernetes. To enable this feature, the kubelet API was extended with an endpoint that enables the creation of checkpoints for individual containers. By default, all container checkpoints are stored as tar archives in /var/lib/kubelet/checkpoints using the following file name format: checkpoint-<pod-name>_<namespace-name>-<container-name>-<timestamp>.tar. However, the current implementation does not provide a mechanism for limiting the number of checkpoints, which may lead to filling up all existing disk space. This project aims to develop a Kubernetes operator that automates the management of checkpoints and provides a garbage collection mechanism to discard obsolete checkpoints.

Links:

Details:

  • Skill level: intermediate
  • Language: Go
  • Expected size: 350 hours
  • Mentors: Adrian Reber <areber@redhat.com>, Radostin Stoyanov <rstoyanov@fedoraproject.org>, Prajwal S N <prajwalnadig21@gmail.com>
  • Suggested by: Adrian Reber

Suspended project ideas[edit]

Listed here are tasks that seem suitable for GSoC, but currently do not have anybody to mentor it.

Optimize logging engine[edit]

Summary: CRIU puts a lots of logs when doing its job. Logging is done with simple fprintf function. They are typically useless, but if some operation fails -- the logs are the only way to find what was the reason for failure.

At the same time the printf family of functions is known to take some time to work -- they need to scan the format string for %-s and then convert the arguments into strings. If comparing criu dump with and without logs the time difference is notable (15%-20%), so speeding the logs up will help improve criu performance.

One of the solutions to the problem might be binary logging. The problem with binary logs is the amount of efforts to convert existing logs to binary form. Preferably, the switch to binary logging either keeps existing log() calls intact, either has some automatics to convert them.

The option to keep log() calls intact might be in pre-compilation pass of the sources. In this pass each log(fmt, ...) call gets translated into a call to a binary log function that saves fmt identifier copies all the args as is into the log file. The binary log decode utility, required in this case, should then find the fmt string by its ID in the log file and print the resulting message.

Links:

Details:

  • Skill level: intermediate
  • Language: C, though decoder/preprocessor can be in any language
  • Expected size: 350 hours
  • Suggested by: Andrei Vagin
  • Mentors: Alexander Mikhalitsyn <alexander@mihalicyn.com>

IOUring support[edit]

The io_uring Asynchronous I/O (AIO) framework is a new Linux I/O interface, first introduced in upstream Linux kernel version 5.1 (March 2019). It provides a low-latency and feature-rich interface for applications that require AIO functionality.

Links:

Details:

  • Skill level: expert (+linux kernel)
  • Expected size: 350 hours

Add support for SPFS[edit]

Summary: The SPFS is a special filesystem that allows checkpoint and restore of such things as NFS and FUSE

NFS support is already implemented in Virtuozzo CRIU, but it's very beneficial to port it to mainline CRIU. The importaint part of it is the need to implement the integration of Stub-Proxy File System (SPFS) with LXC/yet_another_containers_environment.

Links

Details:

  • Skill level: expert
  • Language: C
  • Mentor: Alexander Mikhalitsyn <alexander@mihalicyn.com>
  • Suggested by: Alexander Mikhalitsyn <alexander@mihalicyn.com>


Anonymise image files[edit]

Summary: Teach CRIT to remove sensitive information from images

When reporting a BUG it may be not acceptable for the reporter to send us raw images, as they may contain sensitive data. Need to teach CRIT to "anonymise" images for publication.

List of data to shred:

  • Memory contents. For the sake of investigation, all the memory contents can be just removed. Only the sizes of pages*.img files are enough.
  • Paths to files. Here we should keep the paths relations to each other. The simplest way seem to be replacing file names with "random" (or sequential) strings, BUT (!) keeping an eye on making this mapping be 1:1. Note, that file paths may also sit in sk-unix.img.
  • Registers.
  • Process names. (But relations should be kept).
  • Contents of streams, i.e. pipe/fifo data, sk-queue, tcp-stream, tty data.
  • Ghost files.
  • Tarballs with tmpfs-s.
  • IP addresses in sk-inet-s, ip tool dumps and net*.img.

Links:

Details:

  • Skill level: beginner
  • Language: Python
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