Bits of Google's dead Project Ara modular mobe live on in Linux 4.9

Linus Torvalds teaches devs a lesson with early rc1 release

Google may have killed off its modular smartphone Project Ara idea, but some of the code that would have made it happen looks like coming to the Linux Kernel.

So says none other than Linus Torvalds himself, in his Linux Kernel Mailing List post announcing the first release candidate of Linux 4.9.

Torvalds tossed in a barb with that post, by releasing it on a Saturday afternoon and explaining why as follows:

“I usually do the releases on a Sunday afternoon, but occasionally cut the merge window short by a day just to keep people on their toes, and make sure people learn not to send in last-minute pull requests. No gaming the merge window to the last day. This is one such release.”

Consider yourself chastised, kernel devs!

Torvalds says this will be a conventional release, with lots of bugs to be fixed. But he also called out two new additions.

“The big new thing is the greybus addition, which Greg swears is actually getting used.” “Greg” is kernel developer Greg Kroah-Hartman and “greybus” is this component of Project Ara. As Kroah-Hartman posted last month, “Greybus is an hardware protocol that was designed to provide Unipro with a sane application layer. It was originally designed for the ARA project, a module phone system, but has shown up in other phones, and can be tunneled over other busses in order to control hardware devices.”

So perhaps Google's vision isn't entirely dead.

Torvalds says his favourite addition is “Andy Lutomirski's new virtually mapped kernel stack allocations” because “They make it easier to find and recover from stack overflows, but the effort also cleaned up some code, and added a kernel stack mapping cache to avoid any performance downsides.”

“The virtual stack mapping also happens to mean that people who try to do DMA from temporary buffers on the stack ('Don't do it!') now really need to change their evil ways. So there is some fallout from this, and I expect a couple of drivers to need minor fixes. But it's all for a good cause, really (and it isn't all that common, because doing DMA from the stack really has never been a good idea, and is generally not even workable in most situations).”

Linus final instruction is, as ever, “go forth and test.” El Reg won't get in your way. ®

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