On Wed, Mar 23, 2011 at 10:34:08AM -0400, Jeff Moyer wrote: > Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx> writes: > > > Has anyone successfully used the asynchronous I/O gadgetfs interface > > before? Specifically, has anyone used it for high-bandwidth isochronous > > traffic? > > > > I ask because I remember discovering about four years ago that there > > were several brain-twisty bugs in the in-kernel asynchronous I/O layer > > that gadgetfs uses. > > Weren't they addressed? And are you looking to use the gadgetfs aio > interface now, or are you looking to get rid of it? In other words, > what's the real motivation behind the question? I was looking to use it. The bug in question I remember was about cancellation, but I would have to dig in my mailbox from 2007 to find the exact issue. The biggest problem I remember when I was looking at using the aio core to replace the ioctls in the usbfs subsystem with true aio operations was there was an issue with operation ordering. In the kernel to userspace interface for USB, we want asynchronous operations to a particular file to be queued to the hardware in the order they are submitted. So if the userspace application submits asynchronous read A, then asynchronous read B, then the buffer for read B doesn't get queued to the USB host controller before the buffer for read A. Otherwise you get transmission reordering on the bus, and USB devices aren't very happy. > > The AIO core also seemed to be largely unmaintained. Is this still > > true? > > Surely you should at least cc the aio list when asking such a question! > Anyway, the aio core is maintained by several folks, but nobody is doing > active development in that area, to my knowledge. Sorry, I forgot the aio mailing list existed. :) In 2007, there was lots of talk of using syslets or fibrils in the aio core, and Zack Brown had some patches for that, but it seemed like nothing really came out of that. Has anything new been added to the AIO core since then? Sarah Sharp -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
