Here's the deal. The custom application binds to and on occasion releases USB connections to a controller, /dev/input/js0 (and /dev/input/event4 on my Rpi). It then reclaims it, reinitializes it, and carries on with execution. There's several reasons why it might legitimately release it. Point is, it works fine whilst QLC+ is not running throughout disconnects/reconnects. However, the program relies on QLC+, because it integrates with QLC+'s websocket API.
NOW we come to the problem. With QLC+ running in parallel to the program, when the program release the USB device, QLC+'s (hotplugging scanner?) USB integration comes and swipes the USB device, such that the program cannot reclaim it. And then everything goes to hell.
Sigh. Luckily for me, the program is running as root (yes, I know), and QLC+ is running as my normal user. So, THEORETICALLY, I could use udev to set these devices to be owned by root and restrict permissions to 600 and viola QLC+ couldn't claim them because it couldn't access them. Here's my setup:
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$ cat zzzz-98-usb.rules
# Match the input device (such as /dev/input/js0)
SUBSYSTEM=="input", ATTRS{idVendor}=="0e6f", ATTRS{idProduct}=="0103", KERNEL=="event*|js*", ACTION=="add|bind|change|online", OWNER="root", GROUP="root", MODE="0600", TAG+="systemd", RUN:="/opt/udev/guard.sh /dev/input/%k"Code: Select all
#!/usr/bin/bash
LOGFILE=/var/log/guard.log
DEVICE_PATH=$1
echo "${DEVICE_PATH}: $(/usr/bin/date) Device plugged in." >> $LOGFILE
echo "${DEVICE_PATH}: Unix Permissions" >> $LOGFILE
echo "${DEVICE_PATH}: $(ls -l "${DEVICE_PATH}")" >> $LOGFILE
# Log the ACL before setting it
echo "${DEVICE_PATH}: ACL:" >> $LOGFILE
echo "${DEVICE_PATH}: $(getfacl "${DEVICE_PATH}")" >> $LOGFILE
# Restrict permissions
chown root:root "${DEVICE_PATH}"
chmod 600 "${DEVICE_PATH}"
# Remove ACLs
/usr/bin/setfacl -b "${DEVICE_PATH}"
echo "${DEVICE_PATH}: Permissions set and ACLs removed." >> $LOGFILE
echo "${DEVICE_PATH}: Unix Permissions" >> $LOGFILE
echo "${DEVICE_PATH}: $(ls -l "${DEVICE_PATH}")" >> $LOGFILE
# Log the ACL after setting
echo "${DEVICE_PATH}: ACL:" >> $LOGFILE
echo "${DEVICE_PATH}: $(getfacl "${DEVICE_PATH}")" >> $LOGFILE
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$ ls -l /dev/input
total 0
drwxr-xr-x 2 root root 120 Feb 8 17:12 by-id
drwxr-xr-x 2 root root 160 Feb 8 17:12 by-path
crw-rw---- 1 root input 13, 64 Feb 8 13:18 event0
crw-rw---- 1 root input 13, 65 Feb 8 13:18 event1
crw-rw---- 1 root input 13, 66 Feb 8 13:18 event2
crw-rw---- 1 root input 13, 67 Feb 8 13:18 event3
crw------- 1 root root 13, 68 Feb 8 17:12 event4
crw------- 1 root root 13, 69 Feb 8 17:12 event5
crw------- 1 root root 13, 0 Feb 8 17:12 js0
crw------- 1 root root 13, 1 Feb 8 17:12 js1
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sudo ls -la /dev/input/
total 0
drwxr-xr-x 3 root root 160 Feb 8 17:19 .
drwxr-xr-x 17 root root 4060 Feb 8 17:14 ..
drwxr-xr-x 2 root root 80 Feb 8 17:19 by-path
crw-rw---- 1 root input 13, 64 Feb 8 13:18 event0
crw-rw---- 1 root input 13, 65 Feb 8 13:18 event1
crw-rw---- 1 root input 13, 66 Feb 8 13:18 event2
crw-rw---- 1 root input 13, 67 Feb 8 13:18 event3
crw-rw---- 1 root input 13, 63 Feb 8 13:18 mice
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$ ls -la /dev/input/
total 0
drwxr-xr-x 4 root root 220 Feb 8 17:23 .
drwxr-xr-x 17 root root 4060 Feb 8 17:14 ..
drwxr-xr-x 2 root root 80 Feb 8 17:23 by-id
drwxr-xr-x 2 root root 120 Feb 8 17:23 by-path
crw-rw---- 1 root input 13, 64 Feb 8 13:18 event0
crw-rw---- 1 root input 13, 65 Feb 8 13:18 event1
crw-rw---- 1 root input 13, 66 Feb 8 13:18 event2
crw-rw---- 1 root input 13, 67 Feb 8 13:18 event3
crw------- 1 root root 13, 69 Feb 8 17:23 event5
crw------- 1 root root 13, 1 Feb 8 17:23 js1
crw-rw---- 1 root input 13, 63 Feb 8 13:18 mice
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jforest1 3153 1 4 17:22 pts/1 00:00:08 /usr/bin/qlcplus --open /opt/qlcplus.qxw --web --operate
Is QLC+ magical? I do have a USB device that QLC+ needs for DMX512 output, but how do I keep it away from the other USB devices that I don't want it touching?
Help, I'm at the end of my rope.