> > Agree that's a problem. We just need an alternative interface here > > or I try to come up with an x86-64 specific hack (I think it's possible > > to do the compatibility x86-64 specific, just not in compat code for > > all architectures who have truly separated user/kernel address spaces) > > > > I hope the USB people will eventually add a better interface here. > > Greg? > > Yes, we've been talking about a usbfs2 for a long time now, but no one > has stepped up and done the work. It would look a lot like gadgetfs, > which only has a limited number of ioctls needed for its operation. > > But I don't see where the problem is unique to usbfs here, don't we > properly use the 32->64bit ioctl conversion code to solve this kind of > issue? Are we using it incorrectly?
DaveM can probably give you more details since he tried unsucessfully to make it work. I think the problem is that there is no enough information for the compat layer to convert everything. Here's his comment from fs/compat_ioctl.c. On x86-64 it can be a bit easier because you can get away with only partially converting a data structure because the 32bit space is still visible from the kernel. But that doesn't work on some other archs. -Andi /* This needs more work before we can enable it. Unfortunately * because of the fancy asynchronous way URB status/error is written * back to userspace, we'll need to fiddle with USB devio internals * and/or reimplement entirely the frontend of it ourselves. -DaveM * * The issue is: * * When an URB is submitted via usbdevicefs it is put onto an * asynchronous queue. When the URB completes, it may be reaped * via another ioctl. During this reaping the status is written * back to userspace along with the length of the transfer. * * We must translate into 64-bit kernel types so we pass in a kernel * space copy of the usbdevfs_urb structure. This would mean that we * must do something to deal with the async entry reaping. First we * have to deal somehow with this transitory memory we've allocated. * This is problematic since there are many call sites from which the * async entries can be destroyed (and thus when we'd need to free up * this kernel memory). One of which is the close() op of usbdevicefs. * To handle that we'd need to make our own file_operations struct which * overrides usbdevicefs's release op with our own which runs usbdevicefs's * real release op then frees up the kernel memory. * * But how to keep track of these kernel buffers? We'd need to either * keep track of them in some table _or_ know about usbdevicefs internals * (ie. the exact layout of its file private, which is actually defined * in linux/usbdevice_fs.h, the layout of the async queues are private to * devio.c) * * There is one possible other solution I considered, also involving knowledge * of usbdevicefs internals: * * After an URB is submitted, we "fix up" the address back to the user * space one. This would work if the status/length fields written back * by the async URB completion lines up perfectly in the 32-bit type with * the 64-bit kernel type. Unfortunately, it does not because the iso * frame descriptors, at the end of the struct, can be written back. * * I think we'll just need to simply duplicate the devio URB engine here. */ ------------------------------------------------------- The SF.Net email is sponsored by: Beat the post-holiday blues Get a FREE limited edition SourceForge.net t-shirt from ThinkGeek. It's fun and FREE -- well, almost....http://www.thinkgeek.com/sfshirt _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
