is there a reason "usbhid.quirks" parameter is not root writable?

[rpjday@crashcourse.ca (Robert P. J. Day)]

On Thu, 12 Nov 2015, Greg KH wrote:

> On Thu, Nov 12, 2015 at 03:15:41AM -0700, Robert P. J. Day wrote:
> >
> >   short form: is there some reason that the usbhid "quirks" parameter
> > is not by default compiled to be writable in case you wanted to adjust
> > those values on a running system?
> >
> >   long form: i have a USB device that, sadly, is automatically claimed
> > by the usbhid driver upon insertion, and i want to prevent that so it
> > behaves as a regular USB device. from what i've read, the solution is
> > to, at boot time, add the kernel command line parameter:
> >
> >   usbhid.quirks=0x2123:0x1010:0x04
> >
> > that's fine if i want to reboot so that that takes effect, but it
> > would of course be convenient if i could add that info to
> > /sys/module/usbhid/parameters/quirks at run-time. currently, on my
> > fedora 22 system:
> >
> > $ cat /sys/module/usbhid/parameters/quirks
> > (null),(null),(null),(null)
> > $
> >
> > with permissions:
> >
> > $ ls -l /sys/module/usbhid/parameters/quirks
> > -r--r--r--. 1 root root 4096 Nov 12 02:41 /sys/module/usbhid/parameters/quirks
> > $
> >
> > and i can see in drivers/hid/usbhid/hid-core.c the fact that that
> > array is defined as non-writable:
> >
> > /* Quirks specified at module load time */
> > static char *quirks_param[MAX_USBHID_BOOT_QUIRKS];
> > module_param_array_named(quirks, quirks_param, charp, NULL, 0444);
> > MODULE_PARM_DESC(quirks, "Add/modify USB HID quirks by specifying "
> >                 " quirks=vendorID:productID:quirks"
> >                 " where vendorID, productID, and quirks are all in"
> >                 " 0x-prefixed hex");
> >
> > so the obvious(?) question is, is there some reason that that
> > parameter is defined as read-only rather than, say, writable by root?
> > would it not be useful to be able to modify that parameter at
> > run-time? or is there something about that parameter for which that
> > would be a really bad idea?
>
> You can add a runtime quirk to the device itself when it shows up in
> sysfs for the hid driver.  Use that instead of the module parameter for
> that specific device.

  sorry, i'm not sure what you're suggesting here.

rday

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Robert P. J. Day                                 Ottawa, Ontario, CANADA
                        http://crashcourse.ca

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