On Tue, 2011-10-04 at 08:32 -0700, Greg KH wrote: > On Tue, Oct 04, 2011 at 05:19:13PM +0200, Jack Smith wrote: > > On Tue, 2011-10-04 at 07:57 -0700, Greg KH wrote: > > > If you want the host side of the MTP solution, that too is done in > > > userspace, no kernel driver needed. I think it's in the gphoto library > > > code that uses libusb to talk to the devices. I'd recommend digging > > > around in that. > > > > > OK, so, can I ask why this is done in user space, instead of as a kernel > > module ? > > Because it can :) > > > Also, why are some USB protocols are handled as drivers, e.g. Mass > > Storage, while others are not ? Pardon me asking, but why the > > inconsistency ? > > A USB driver is done in the kernel if it needs to provide the interface > to userspace in a consistant manner like other types of devices of the > same type. > > So, for a usb storage device, it needs to act like a "normal" block > device, so the driver is in the kernel so that userspace doesn't need to > know about what type of device this is (scsi, ata, ide, usb, etc.) Same > goes for USB video cameras, they have a kernel driver that exposes to > userspace a "normal" video device. > > But, for other devices that do not have a corrisponding "traditional" > way to be exposed to userspace, like the MTP api describes), and there > are no speed or performance benifits from being within the kernel, then > those will be implemented as userspace drivers, using libusb or usbfs > directly. > > > > Hope this helps, > > > > > Yes, very helpful, but: > > > > The thing is, I really want to work on device drivers. It seemed like > > USB-MTP would be a good candidate since USB is clearly not going away, > > and MTP seems fairly poorly supported within Linux (unless I'm missing > > something). > > Look at the libgphoto library, I think all of the code you want to use > is there. > OK, I'll have a look. > And yes, writing device drivers is fun, but we only do it if it is > necessary. Sometimes making a driver actually makes things more complex > than if we did it only as a userspace driver. > > Take this protocol for example, how would you export the MTP interface > to userspace in a manner that would be easy for userspace programs to > interact with it? Good point. The voice of experience shines through. Thanks again for your help. > > thanks, > > greg k-h -- 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
