RFR: 8201568: zForce touchscreen input device fails when closed and immediately reopened

[Johan Vos]

On Mon, 29 Jun 2020 18:49:33 GMT, John Neffenger <github.com+1413266+jgneff at openjdk.org> wrote:

>> The rationale makes sense (open/open/close) instead of (open/close/open)
>
> Based on my notes below, I believe this change is safe for any Linux input device driver because the driver shouldn't
> receive the intermediate *open* and *close* calls at all.
> Nonetheless, it would be reassuring if someone could try [this change](https://github.com/openjdk/jfx/pull/258/files)
> just once on a mainstream device, such as the Raspberry Pi with a touchscreen LCD panel. I only have six obscure ARM
> devices and a headless QEMU ARM virtual machine for testing. @johanvos or @dellgreen - Is that something you could
> test? If you think it's overkill and not worth it, that's fine, too.  #### Notes
> The Linux kernel documentation about [opening and
> closing](https://www.kernel.org/doc/html/latest/input/input-programming.html#dev-open-and-dev-close) input devices
> states:
>> Note that input core keeps track of number of users for the device and makes sure that dev->open() is called only when
>> the first user connects to the device and that dev->close() is called when the very last user disconnects. Calls to
>> both callbacks are serialized.
> 
> Also, the Linux Programmer's Manual for the *close* system call (`man 2 close`) states:
> 
>> If *fd* is the last file descriptor referring to the underlying open file description (see **open**(2)), the resources
>> associated with the open file description are freed.
> 
> Running a JavaFX program with `strace -f -e trace=open,close -o strace.log` shows the one *open* for the *event0*
> keyboard, and the *open, open, close* for the *event1* touchscreen:
> 5847  open("/dev/input/event0", O_RDONLY) = 11
> ...
> 5847  open("/dev/input/event1", O_RDONLY) = 12
> 5847  open("/dev/input/event1", O_RDONLY) = 13
> 5847  close(13)                         = 0
> 
> Both devices are actually closed by the kernel when the JavaFX program ends.

I don't have access to a Pi right now, so I can't test this (I'll be able to test in about 10 days from now though)

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PR: https://git.openjdk.java.net/jfx/pull/258