Re: [PATCH] Add support for usbfs zerocopy.

[Steinar H. Gunderson]

On Wed, Jan 06, 2016 at 04:22:12PM +0100, Peter Stuge wrote:
>>> 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.
> How about aio?

I don't really see how; a USB device does not look much like a file. (Where
would you stick the endpoint, for one? And how would you ever submit an URB
with multiple packets in it, which is essential?) It feels a bit like
trying to use UDP sockets with only read() and write().

In any case, the usbfs interface already exists and is stable. This is about
extending it; replacing it with something new from scratch to get zerocopy
would seem overkill.

/* Steinar */
-- 
Software Engineer, Google Switzerland
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