On Tue, Apr 30, 2024 at 06:25:13PM -0400, Jason Andryuk wrote: > On Mon, Apr 29, 2024 at 9:04 PM Jason Andryuk <jandryuk@xxxxxxxxx> wrote: > > > > On Mon, Apr 29, 2024 at 5:50 PM Dmitry Torokhov > > <dmitry.torokhov@xxxxxxxxx> wrote: > > > > > > 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@xxxxxxxxx> > > > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx> > > > > Tested-by: Jason Andryuk <jandryuk@xxxxxxxxx> > > > > I don't have the gdm setup available to test, but loginctl looks good > > showing the Xen Virtual Keyboard assigned to a seat: > > # loginctl seat-status seat0 > > seat0 > > Devices: > > ├─/sys/devices/LNXSYSTM:00/LNXPWRBN:00/input/input0 > > │ input:input0 "Power Button" > > ├─/sys/devices/LNXSYSTM:00/LNXSLPBN:00/input/input1 > > │ input:input1 "Sleep Button" > > ├─/sys/devices/platform/i8042/serio0/input/input2 > > │ input:input2 "AT Translated Set 2 keyboard" > > ├─/sys/devices/platform/i8042/serio1/input/input4 > > │ input:input4 "ImExPS/2 Generic Explorer Mouse" > > ├─/sys/devices/virtual/input/input5 > > │ input:input5 "Xen Virtual Keyboard" > > │ └─/sys/devices/virtual/input/input5/event4 > > │ input:event4 > > └─/sys/devices/virtual/input/input6 > > input:input6 "Xen Virtual Pointer" > > What do you think about Cc: stable@xxxxxxxxxxxxxxx? I'd like to get > the Xen Keyboard working as widely as possible, so I'd like it > backported if possible. I am open to it, but I'd like Benjamin/Hans to take a look at this as well (I see Peter already gave his Reviewed-by). Thanks. -- Dmitry
