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

[Robert P. J. Day]

  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?

rday

-- 

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

Twitter:                                       http://twitter.com/rpjday
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