Linux Is About To Lose A Feature – Over A Personality Clash

comment The first release candidate of Linux 6.17 is out, without any bcachefs changes… but not for any technical reasons. This is bad.

As we reported recently, kernel 6.17 is approaching. Linus Torvalds announced the first release candidate on Sunday, August 10. Of course, he is irked about something – that’s not unusual – but this time his ire is directed at late RISC-V patches.

However, as Phoronix notes, there is no new bcachefs code in this version so far. Developer Kent Overstreet did submit some minor changes at the end of July, saying:

So, the experimental label is coming off in 6.18.

However, Torvalds has not accepted the code. As we reported earlier in July, it looks like – without any official comment — the stable version of Linux’s newest file system, first included in version 6.7, will not appear in kernel 6.18.

Boxout

As it happens, Canonical has been planning to use kernel 6.17 in the forthcoming Ubuntu 25.10, Questing Quokka, since May. As of this week, Questing is now in feature freeze, and Canonical will probably still use that kernel version even if the final version hasn’t been released yet come October. Given the time frame, it’s likely that 6.17 will be the last version of 2025, and as such, will probably be the next LTS version of the kernel.

End boxout

Development of the Linux kernel is coordinated through a mailing list known as the LKML. Overstreet’s code submission now has a lengthy thread. Overstreet has criticized rival Btrfs, saying:

When brtfs shipped, it did so with clear design issues that have never been adequately resolved.

[…]

As a result, to this day, people don’t trust it, and for good reason.

This is true. This vulture has personally experienced serious problems with Brtfs, and has written about them, as well as linking to others’ coverage. Red Hat removed it from RHEL in 2017, although Oracle puts it back into its RHELative. These are not baseless accusations, as this recent Hackernews discussion bears out.

This is not a new thing. As we have written before, we remain sure that this is why the bcachefs slogan, in large (but perhaps not very friendly) letters across the top of the project website is: “The COW filesystem for Linux that won’t eat your data”. It’s a dig at Btrfs.

The issues are real. Such problems need to be discussed. However, what in fact happened was a spirited defence of Btrfs from Meta developer Josef Bacik, concluding with:

Your behavior is unacceptable. This email is unacceptable.

[…]

If you are allowed to continue to be in this community that will be a travesty.

Overstreet responded with a reasoned rebuttal, but that angered ext4 developer Ted Ts’o:

Kent, you seem to have ignored the primary point of Josef’s message, and instead, proceeded to prove exactly what he was pointing out.

[…]

You once again demonstrated exactly why a very large number of kernel developers have decided you are extremely toxic, and have been clamoring that your code be ejected from the kernel. Not because of the code, but because your behavior.

We feel a little context might help here. On the one hand, Ted Ts’o is one of the most eminent filesystem engineers in the Linux project, and maintains the default ext4 filesystem. On the other hand, Ts’o’s outburst directed at Wedson Filho, the maintainer of Rust for Linux, at a conference last year was closely followed by Filho’s resignation due to “nontechnical nonsense”.

Overstreet has sworn not to criticize Btrfs again. Others have backed up his criticisms, and his position. Critics, meanwhile, suggest that he seek psychotherapy, or accuse him of mental illness, or call him a liar. As a whole, it has not been an impressive or dignified debate. The hurt feelings and personal accusations on display are ignoble, to say the least.

The whole incident emphasizes the extent to which these ostensibly technical debates are often settled by personality and emotion, rather than by technical excellence.

It’s not the first time that the kernel team has favored what to external observers seems like the inferior tool. As we previously described, over 20 years ago, the kernel team faced a choice between two rival logical volume management systems: either EVMS, which was backed by IBM, or LVM2 from Sistina Software, which ended up getting acquired by Red Hat.

As the EVMS Wikipedia article notes, “EVMS had more features and better userland tools, but the internals of LVM were more attractive to kernel developers, so in the end LVM won the battle for inclusion.” Never mind the poor users, eh? The EVMS team published an extraordinarily graceful message of concession and it disappeared soon afterwards.

It looks likely that Overstreet has upset too many important, influential people, and hurt too many feelings — and as a result, Linux is not going to get a new next-gen copy-on-write filesystem. It’s a significant technological loss, and it’s all down to people not getting along, rather than the shared desire to create a better OS. ®

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