Linux 5.10 is a bigger kernel release than expected and sees the removal of setf_fs()
With first release candidate of version 5.10 of the Linux kernel now available, Linus Torvalds says that it "looks to be a bigger release" than he expected.
Linux kernel 5.10-rc1 includes 14-15,000 merge commits -- depending on how you count them -- Torvalds notes in his weekly update to the Linux community. He shares the news that, for him, the most interesting change in this release is the removal of the setf_fs() addressing tool.
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Torvalds concedes that getting rid of setf_fs() is not exactly an Earth-shattering change, but it is an important one nonetheless. He explains: "The most interesting -- to me -- change here is Christoph's setf_fs() removal (it got merged through Al Viro, as you can see in my mergelog below). It's not a _huge_ change, but it's interesting because the whole model of set_fs() to specify whether a userspace copy actually goes to user space or kernel space goes back to pretty much the original release of Linux, and while the name is entirely historic (it hasn't used the %fs segment register in a long time), the concept has remained. Until now".
He goes on to say:
We still do have "set_fs()" around, and not every architecture has been converted to the new world order, but x86, powerpc, s390 and RISC-V have had the address space overrides removed, and all the core work is done. Other architectures will hopefully get converted away from that very historic model too, but it might take a while to get rid of it all.
Anyway, to most people that all shouldn't matter at all, and it's mainly a small historical footnote that 5.10 no longer relies on the whole set_fs() model.
You can see his full post -- which includes the full mergelog -- here.