On Tue, Jun 04, 2013 at 12:49:36AM +0200, Markus Grabner wrote: > On Sunday 20 January 2013 23:51:36 Markus Grabner wrote: > > Am Sonntag, 20. Januar 2013, 09:11:50 schrieb Greg Kroah-Hartman: > > > On Sat, Jan 19, 2013 at 10:55:29PM +0100, Markus Grabner wrote: > > > > Am Freitag, 18. Januar 2013, 16:57:31 schrieb Greg Kroah-Hartman: > > > > > On Fri, Jan 18, 2013 at 10:52:14PM +0100, Markus Grabner wrote: > > > > > > The function "line6_send_raw_message_async" now has an additional > > > > > > argument > > > > > > "bool copy", which indicates whether the supplied buffer should be > > > > > > copied > > > > > > into a dynamically allocated block of memory. The copy flag is also > > > > > > stored in the "message" struct such that the temporary memory can be > > > > > > freed when appropriate without intervention of the caller. > > > > > > > > > > Why do this? Why not either always copy it, or always not? > > > > > > > > Some messages are sent to the device which have no parameters, they are > > > > declared at global scope as constant byte arrays and therefore must be > > > > copied into a dynamically allocated block of memory in order to be sent > > > > over the USB interface. On the other hand, there are messages which do > > > > have parameters and which are composed in dynamically allocated memory > > > > and can therefore directly be sent without copying. > > > > > > Then if you always copy the memory, and "own" it after the call, you > > > should be fine, right? > > > > > > > > What is this fixing? > > > > > > > > Two users reported to me independently that the driver doesn't work for > > > > them. I couldn't reproduce the problem since it seems to be triggered by > > > > subtle timing issues in the system, but after some further > > > > investigations, the kfree() of the message buffer immediately after > > > > submitting the message for asynchronous transmission was clearly > > > > identified as the reason for the driver not working. The patch puts the > > > > kfree() at the right place and (hopefully) prevents incorrect use of the > > > > new buffer copy feature. The patch is tested by me and the users who > > > > initially reported the bug, and they confirmed that the issue is fixed > > > > for them. > > > > > > > > If anybody has a better idea how to fix this, please go ahead! The patch > > > > might also become obsolete in the future due to refactoring. But > > > > currently there is a bug which prevents some people from using the > > > > driver > > > > at all, and this should be fixed soon IMO. > > > > > > I agree, it should be fixed, but having the code always do the copy and > > > manage the memory, and not have the crazy "flag" option, should solve > > > the bug for everyone. > > > > Removing the flag saves three lines of code, keeping the flag saves a tiny > > amount of time and memory, so it's not really worth a lengthy discussion, > > and I actually don't care much. I will focus on the user space library I'm > > currently working on since it will make much of the MIDI-related Line6 > > kernel driver code obsolete. > I'm currently re-investigating this, and I have been informed by users that > some newer Line6 devices talk a device-specific protocol over USB which is > different from the MIDI standard and should therefore not be mapped to a > virtual MIDI device. This raises some additional questions: > > *) The easiest way to deal with this would be to use libusb in user space to > exchange data with the device. However, as far as I understand, if the device > is being used as an ALSA sound card (i.e., the kernel driver has claimed the > USB interface to access isochronous endpoints), libusb can't access interrupt > endpoints of the same interface at the same time since it can't claim the > interface while it is claimed by the kernel. Is this correct? Yes, that is correct. > *) If shared kernel/user space access to the same USB interface is not > possible as discussed above, what would be the preferred interface for user > space applications to talk to the kernel driver? I think netlink is a good > candidate, or do you have any other suggestions? What exactly do you need to communicate from user to kernel? That is going to dictate what interface to use. thanks, greg k-h -- To unsubscribe from this list: send the line "unsubscribe kernel-janitors" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
