Btrfs-progs

Userspace utilities to manage btrfs filesystems. License: GPLv2.

Btrfs is a copy on write (COW) filesystem for Linux aimed at implementing advanced features while focusing on fault tolerance, repair and easy administration.

This repository hosts following utilities and also documentation:

• btrfs — the main administration tool (manual page)
• mkfs.btrfs — utility to create the filesystem (manual page)
• all-in-one binary in the busybox style with mkfs.btrfs, btrfs-image and other tools built-in (standalone tools)
• libbtrfsutil (LGPL v2.1) — C and python 3 bindings, see libbtrfsutil/README.md for more
• manual pages and documentation source published at btrfs.readthedocs.io (RTD)

See INSTALL for build instructions, tests/README.md for testing information and ci/README.md for CI information.

Release cycle

The major version releases are time-based and follow the cycle of the linux kernel releases. The cycle usually takes 2 months. A minor version releases may happen in the meantime if there are bug fixes or minor useful improvements queued.

The release tags are signed with a GPG key ID F2B4 1200 C54E FB30 380C 1756 C565 D5F9 D76D 583B, release tarballs are hosted at kernel.org. See file CHANGES or changelogs on RTD.

Releases with changelog are also published at Github release page.

Static binaries

For each release there are static binaries of btrfs and btrfs.box provided. These can be used in rescue environments and are built for x86_64 architecture (with maximum backward compatibility), inside the Github Actions workflow. The btrfs.box is an all-in-one tool in the busybox style, the functionality is determined by the binary names (either symlink, hradlink or a file copy).

Feature compatibility

The btrfs-progs of version X.Y declare support of kernel features of the same version. New progs on old kernel are expected to work, limited only by features provided by the kernel.

Build compatibility

Build is supported on the GNU C library as the primary target, and on the musl libc.

The supported compilers are gcc (minimal version 4.8) and clang (minimal version 3.4).

Build tests are done on several distributions, see Github actions workflow.

Reporting bugs

There are several ways, each has its own specifics and audience that can give feedback or work on a fix. The following list is sorted in the order of preference:

• Github issue tracker
• to the mailing list linux-btrfs@vger.kernel.org -- (not required to subscribe), beware that the mail might get overlooked in other traffic
• IRC (irc.libera.chat #btrfs) -- good for discussions eg. if a bug is already known, but reports could miss developers' attention
• please don't use https://bugzilla.kernel.org for btrfs-progs bugs

Development

The development takes place in the mailing list (linux-btrfs@vger.kernel.org) or at Github (issues, pull requests). Changes should be split to logical parts if possible, documentation may be included in the same patch as to code or separately.

The development model of btrfs-progs shares a lot with the kernel model. The

• one logical change per patch: e.g. not mixing bugfixes, cleanups, features etc., sometimes it's not clear and will be usually pointed out during reviews
• proper subject line: e.g. prefix with btrfs-progs: subpart, ... , descriptive yet not too long, see git log --oneline for some inspiration
• proper changelog: the changelogs are often missing or lacking explanation why the change was made, or how is something broken, what are user-visible effects of the bug or the fix, how does an improvement help or the intended usecase
• the Signed-off-by line is not mandatory for less significant changes (typos, documentation) but is desired as this documents who authored the change, you can read more about the The Developer's Certificate of Origin (chapter 11)
  • if you are not used to the signed-off style, your contributions won't be rejected just because of it's missing, the Author: tag will be added as a substitute in order to allow contributions without much bothering with formalities

Pull requests

The pull requests on Github may be used for code or documentation contributions. There are basic build checks enabled in the Github actions CI for pull requests. The status can be checked at the workflow page.

• open a PR against branches devel or master
• push update to the same branch if you need to
• close the PR in case it's wrong, a mistake or needs rework
• if you're sure the changes don't need a CI build verification, please add [skip ci] to the changelog

Source code coding style and preferences follow the kernel coding style. You can find the editor settings in .editorconfig and use the EditorConfig plugin to let your editor use that, or update your editor settings manually.

Testing

The documentation for writing and running tests can be found in tests/ and continuous integration/container images in ci/.

Development branches are tested by Github Action workflows.

Code coverage provided by codecov.io can be found here.

Documentation updates

Documentation fixes or updates do not need much explanation so sticking to the code rules in the previous section is not necessary. GitHub pull requests are OK, patches could be sent to me directly and not required to be also in the mailing list. Pointing out typos via IRC also works, although might get accidentally lost in the noise.

Documentation sources are written in RST and built by sphinx.

Third-party sources

Build dependencies are listed in INSTALL. Implementation of checksum/hash functions is provided by copies of the respective sources to avoid adding dependencies that would make deployments in rescue or limited environments harder. The implementations are portable and there are optimized versions for some architectures. Optionally it's possible to use libgcrypt, libsodium, libkcapi, Botan or OpenSSL implementations.

The builtin implemtations uses the following sources: CRC32C, XXHASH, SHA256, BLAKE2.

Some other code is borrowed from kernel, eg. the raid5 tables or data structure implementation (list, rb-tree).

References

• Documentation
• Manual pages
• Changes -- btrfs-progs
• Features by kernel version