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List:       openjdk-openjfx-dev
Subject:    Re: RFR: 8201568: zForce touchscreen input device fails when closed and immediately reopened
From:       John Neffenger <github.com+1413266+jgneff () openjdk ! java ! net>
Date:       2020-06-29 18:51:39
Message-ID: 8--OACSjfgvu2du_DnLxqAoTAIH7MwSdGpxkQAyuf7M=.2085b45b-18a3-4dad-beee-3abf1c0220cf () github ! com
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On Mon, 29 Jun 2020 11:26:50 GMT, Johan Vos <jvos@openjdk.org> wrote:

> > Fixes [JDK-8201568](https://bugs.openjdk.java.net/browse/JDK-8201568).
> 
> 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.

-------------

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


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