linux-kernel - Re: [PATCH] Add support for usbfs zerocopy.

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Message-ID: <Pine.LNX.4.44L0.1601061038101.1579-100000@iolanthe.rowland.org>
Date:	Wed, 6 Jan 2016 10:39:15 -0500 (EST)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Peter Stuge <peter@...ge.se>
cc:	"Steinar H. Gunderson" <sesse@...gle.com>,
	Christoph Hellwig <hch@...radead.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] Add support for usbfs zerocopy.

On Wed, 6 Jan 2016, Peter Stuge wrote:

> Steinar H. Gunderson 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?

aio is not zerocopy.  And it also doesn't solve the memory allocation 
problem that originally affected both Steiner and Markus.

(Were you thinking of "asynchronous" instead of "isochronous"?)

Alan Stern

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