Linked by Thom Holwerda on Sun 22nd Jul 2007 00:33 UTC, submitted by liquidat
Linux Linus Torvalds included patches into the mainline tree which implement a stable userspace driver API into the Linux kernel. The stable driver API was already announced a year ago by Greg Kroah-Hartman. Now the last patches were uploaded and the API was included in Linus' tree. The idea of the API is to make life easier for driver developers: "This interface allows the ability to write the majority of a driver in userspace with only a very small shell of a driver in the kernel itself. It uses a char device and sysfs to interact with a userspace process to process interrupts and control memory accesses."
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RE: Useful API? Useless API !
by butters on Sun 22nd Jul 2007 05:16 UTC in reply to "Useful API? Useless API !"
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You make several good points. There's a fundamental trade-off between performance and isolation. The line in the sand between the kernel and userspace used to be the star of the debate, and now we have guest kernels to worry about.

A few of the shortcomings you mention can be addressed. For example, DMA and memory-mapped I/O can be emulated in userspace in much the same way as they are emulated in high-memory. Bounce-buffering strategies such as the Linux kernel's SWIOTLB service are pretty much the best-case scenario for virtualizing framebuffers and other memory apertures in software. The only way to improve on this is hardware acceleration via enhanced IOMMU functionality.

Isolation is a big deal in computer science today, and we'll no doubt see many innovations in the next decade that will allow hardware and software to manage memory protection in more sophisticated ways. Remember, some commercial UNIX systems still have a fixed segmented memory model. We're only taking the first baby steps toward flexible, high-performance memory protection. The rest will come in due time.

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