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0774d19038
If an input device declares too many capability bits then modalias string for such device may become too long and not fit into uevent buffer, resulting in failure of sending said uevent. This, in turn, may prevent userspace from recognizing existence of such devices. This is typically not a concern for real hardware devices as they have limited number of keys, but happen with synthetic devices such as ones created by xen-kbdfront driver, which creates devices as being capable of delivering all possible keys, since it doesn't know what keys the backend may produce. To deal with such devices input core will attempt to trim key data, in the hope that the rest of modalias string will fit in the given buffer. When trimming key data it will indicate that it is not complete by placing "+," sign, resulting in conversions like this: old: k71,72,73,74,78,7A,7B,7C,7D,8E,9E,A4,AD,E0,E1,E4,F8,174, new: k71,72,73,74,78,7A,7B,7C,+, This should allow existing udev rules continue to work with existing devices, and will also allow writing more complex rules that would recognize trimmed modalias and check input device characteristics by other means (for example by parsing KEY= data in uevent or parsing input device sysfs attributes). Note that the driver core may try adding more uevent environment variables once input core is done adding its own, so when forming modalias we can not use the entire available buffer, so we reduce it by somewhat an arbitrary amount (96 bytes). Reported-by: Jason Andryuk <jandryuk@gmail.com> Reviewed-by: Peter Hutterer <peter.hutterer@who-t.net> Tested-by: Jason Andryuk <jandryuk@gmail.com> Link: https://lore.kernel.org/r/ZjAWMQCJdrxZkvkB@google.com Cc: stable@vger.kernel.org Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>