Why bcachefs Was Dropped from Linux 6.17 – Linus’s Fury and COW Outlook

21CTO Digest: Linus appears angry again as the latest Linux kernel discards an important feature.

Students, good news: the first release candidate of Linux 6.17 has been published, but it contains no bcachefs changes—this omission is not due to any technical reason.

Linus Torvalds announced the RC1 on Sunday, August 10, and, as usual, his anger this time is directed at the long‑overdue RISC‑V patches.

Phoronix noted that this version does not include new bcachefs source code.

bcachefs is an advanced copy‑on‑write (COW) filesystem for Linux, aiming to provide high‑level features while emphasizing fault tolerance, repairability, and ease of management. It combines filesystem and volume‑manager capabilities, offering snapshots, subvolumes, RAID, compression, and checksums.

Kent Overstreet, the developer behind bcachefs, submitted minor changes at the end of July and wrote on the mailing list, "The experimental tag will disappear in 6.18." However, Torvalds has not accepted the code, and there is no official comment—bcachefs will not appear in Linux 6.18.

Canonical has been planning to ship the 6.17 kernel in the upcoming Ubuntu 25.10 "Questing Quokka" release, which entered feature freeze this week and is slated for an October launch. Given the circumstances, 6.17 is likely to become the last kernel release of 2025 and may become the next LTS version.

Linux kernel development is coordinated through the LKML mailing list. In Overstreet’s post, he criticized the competing Btrfs filesystem, stating, "When Btrfs was released it had obvious design flaws that have not been fully resolved… people still don’t trust it, and there are good reasons for that."

Red Hat removed Btrfs from RHEL in 2017, while Oracle later re‑introduced it. These claims have been corroborated by discussions on Hacker News.

Josef Bacik from Meta defended Btrfs vigorously, writing, "Your behavior is unacceptable. This email is unacceptable." (partial text omitted).

Overstreet later swore never to criticize Btrfs again, but others continue to support his stance. Some opponents suggested he seek psychological help, labeling his behavior as abusive.

The episode shows that personal and emotional conflicts, rather than purely technical merits, can drive the direction of kernel features.

Historically, the kernel team has favored tools perceived as higher quality by external observers. Over two decades ago, a battle between the EVMS logical volume manager and LVM2 ended with LVM winning because its internal mechanisms appealed more to kernel developers.

In summary, Overstreet’s actions have alienated many key contributors, and as a result Linux will no longer support a next‑generation COW filesystem. The loss of bcachefs is a significant technical setback caused by interpersonal friction rather than a shared vision for a better operating system.

Author: Kernel Veteran Wang Reference: https://www.theregister.com/2025/08/15/sad_end_of_bcachefs/