Messages in this thread | | | Date | Wed, 6 Jan 2016 15:45:12 +0100 | From | "Steinar H. Gunderson" <> | Subject | Re: [PATCH] Add support for usbfs zerocopy. |
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On Tue, Jan 05, 2016 at 10:49:49PM -0800, Christoph Hellwig wrote: > This is a completely broken usage of the mmap interface. if you use > mmap on a device file you must use the actual mmap for the data > transfer.
Really? V4L does exactly the same thing, from what I can see. It's just a way of allocating memory with specific properties, roughly similar to hugetlbfs.
> Our interface for zero copy reads/writes is O_DIRECT, and that requires > not special memory allocation, just proper alignment.
But that assumes you are using I/O using read()/write(). There's no way you can shoehorn USB isochronous reads into the read() interface, O_DIRECT or not.
/* Steinar */ -- Software Engineer, Google Switzerland
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