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

John Neffenger github.com+1413266+jgneff at openjdk.java.net
Mon Jun 29 18:51:39 UTC 2020

The message from this sender included one or more files
which could not be scanned for virus detection; do not
open these files unless you are certain of the sender's intent.

On Mon, 29 Jun 2020 11:26:50 GMT, Johan Vos <jvos at 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

> 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

More information about the openjfx-dev mailing list