Hi, On 06/29/2012 06:16 PM, Alan Stern wrote:
On Fri, 29 Jun 2012, Hans de Goede wrote:There are a few (new) usbdevfs capabilities which an application cannot discover in any other way then checking the kernel version. There are 3 problems with this: 1) It is just not very pretty 2) Given the tendency of enterprise distros to backport stuff it is not reliable 3) Some of these features turn out to not work with certain host controllers, making depending on them based on the kernel version not a good idea This patch besides adding the new ioctl also adds flags the following existing capabilities: USBDEVFS_CAP_ZERO_PACKET, available since 2.6.31 USBDEVFS_CAP_BULK_CONTINUATION, available since 2.6.32, except for XHCI USBDEVFS_CAP_NO_PACKET_SIZE_LIM, available since 3.3 Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>+static int proc_get_capabilities(struct dev_state *ps, void __user *arg) +{ + __u32 caps = 0; + + caps |= USBDEVFS_CAP_ZERO_PACKET | USBDEVFS_CAP_NO_PACKET_SIZE_LIM;I'd still prefer to get rid of the "= 0" initializer and change this "|=" to simply "=". It's not a big deal though; if the compiler is smart enough it optimize away the first assignment anyhow.
Ah, yes, will change in next revision.
--- a/include/linux/usbdevice_fs.h +++ b/include/linux/usbdevice_fs.h @@ -125,6 +125,11 @@ struct usbdevfs_hub_portinfo { char port [127]; /* e.g. port 3 connects to device 27 */ }; +/* Device capability flags */ +#define USBDEVFS_CAP_ZERO_PACKET 0x01 +#define USBDEVFS_CAP_BULK_CONTINUATION 0x02 +#define USBDEVFS_CAP_NO_PACKET_SIZE_LIM 0x04This raises an interesting question. What happens if someone tries to compile a program for an up-to-date kernel but under an old userspace? These definitions won't be present in /usr/include/linux/. But I guess the same sort of thing happens whenever the kernel's ABI is updated...
Right, libusb solves this by having its own private copy of usbdevice_fs.h, which gets updated every time libusb starts using new ABI. Similar things are done for some v4l2 apps which tend to use the latest ABI (ie libv4l). Regards, Hans -- 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
