On Wed, 2 Jul 2014, Oliver Neukum wrote: > On Wed, 2014-07-02 at 17:53 +0200, Stefan Klug wrote: > > > Implementation details: > > The patch only touches drivers/usb/core/devio.c. > > In procy_do_submiturb(), it is checked if zerocopy is allowed. This is > > currently a rough > > check which compares the number of required pages to > > ps->dev->bus->sg_tablesize. > > It seems to me that the check is per call, so using > multiple calls one could still pin unlimited amounts > of memory. usbfs keeps track of the total amount of pinned memory and enforces an overall limit. It will be necessary to add the size of the transfer buffer to that total. > > I don't know if there is more to check there. > > Then the user memory provided inside the usbdevfs_urb structure is > > pinned to > > physical memory using get_user_pages_fast(). > > All the user pages are added to the scatter-gather list and the logic > > continues as before. > > How do you enforce the cache coherency rules? There is no way to do this. If the user program accesses memory when it shouldn't, the transfer might not work right. > Also you don't have a fall back if get_user_pages_fast() > returns less than requested. It seems to me that than you > ought to fall back buffered IO. Agreed. Alan Stern -- 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
