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Resistance to Rust abstractions for DMA mapping

[LWN subscriber-only content] While the path toward the ability to write device drivers in Rust has been anything but smooth, steady progress has been made and that goal is close to being achieved — for some types of drivers at least. Device drivers need to be able to set up memory areas for direct memory access (DMA) transfers, though; that means Rust drivers will need a set of abstractions to interface with the kernel's DMA-mapping subsystem.

These include maintaining cache coherency, ensuring that pages are resident in RAM, handling device-specific addressing limitations, programming I/O memory-management units, and more. The conversation then went quiet for several days, after which Krummrich said: " Since there hasn't been a reply so far, I assume that we're good with maintaining the DMA Rust abstractions separately". A change of this magnitude to a body of code as large as the kernel was never going to be a quick or easy affair; it has gone as well as could have been expected so far, but there will be more, perhaps harder, obstacles to overcome in the future.

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