[DEPRECATED - see https://github.com/Leo-PL/my-openwrt-packages/tree/master/utils/persistent-serial} Persistent serial port names for USB-serial on OpenWrt hotplugd

10-persistent-serial.sh

[ "${ACTION}" = "add" -o "${ACTION}" = "remove" ] || exit 0
[ "${SUBSYSTEM}" = "tty" ] || exit 0
[ -n "${DEVNAME}" -a -n "${DEVPATH}" ] || exit 1

if [ "${ACTION}" = "add" ]; then
        subsystem="$(basename $(readlink /sys${DEVPATH}/../../../subsystem))"

        [ "$subsystem" = "usb" ] || exit 0

        manufacturer="$(cat /sys${DEVPATH}/../../../../manufacturer)" || manufacturer="$(cat /sys${DEVPATH}/../../../../idVendor)"
        product="$(cat /sys${DEVPATH}/../../../../product)" || product="$(cat /sys${DEVPATH}/../../../../idProduct)"
        serial="$(cat /sys${DEVPATH}/../../../../serial)"
        interface="$(cat /sys${DEVPATH}/../../../bInterfaceNumber)"
        port="$(cat /sys${DEVPATH}/device/port_number)"

        id_link=$(echo "${subsystem}"-"${manufacturer}"_"${product}${serial:+_}${serial}"-if"${interface}${port:+-port}${port}" | s/[^\.\:0-9A-Za-z-]/_/g)
        path_link=$(echo "${DEVPATH}${port:+-port}${port}" | sed s%/devices/%% | sed s%/${DEVNAME}/tty/${DEVNAME}%%g | sed s/[^\.\:0-9A-Za-z-]/_/g)

        mkdir -p /dev/serial/by-id /dev/serial/by-path
        ln -sf "/dev/${DEVNAME}" "/dev/serial/by-id/${id_link}"
        ln -sf "/dev/${DEVNAME}" "/dev/serial/by-path/${path_link}"
elif [ "${ACTION}" = "remove" ]; then
        for link in $(find /dev/serial -type l); do
                [ -L ${link} -a "$(readlink ${link})" = "/dev/$DEVNAME" ] && rm ${link}
        done
fi

i'll give it a try with cp, cause hardlink with ln does not work, but thanks 🙂

Hi,
On line 12, serial is set, but it is never used. Was this intentional? On two udev systems I have here (ubuntu 22.04, CentOS 7), the serial number appears after the product string. For example:
usb-FTDI_FT232R_USB_UART_B0009WPF-if00-port0
usb-FTDI_TTL232RG-VIP_FT3Z78MG-if00-port0

Huh, it looks like I forgot to include it for some reason :-D
I'll push updated version when I test it out.
Edit: done, please try it out. Should work even if serial attribute is missing from the device, like with cheap CH341 adapters. I'm thinking about submitting this script upstream.

Thanks. The serial number is now present.

Looking at this further, I noticed some other things.

1. Is the intent to mimic udev behavior? If so, the sed command at the end of line 16 is problematic. For example, under udev, my FTDI FT230X-based device shows up like this: usb-ACME_coyote_serial-v1.0_FT50OA8O-if00-port0. Using your script with OpenWRT, it looks like this: usb-ACME_coyote_serial-v1_0_FT50OA8O-if00-port0. Perhaps '.' and ':', and possibly other characters should also be excluded from being mangled. I could try to track down the udev code that does this if that would be helpful.
2. I wonder if the script should be using bind/unbind rather than add/remove. The only reason for saying this is because of reading this https://lwn.net/Articles/837033/ on lwn.net. For simple serial devices, waiting for the bind event is likely unnecessary, but in the future there may be devices where waiting for bind is needed. The script would need tweaking to use bind. If you're interested in this, I can modify the script to support it.
3. This likely isn't your department, but the OpenWRT hotplug documentation doesn't even mention tty events. I took me a while to realize that I needed to create the /etc/hotplug.d/tty directory and place my script in there. This was before I discovered your script today. If you happen to know someone within the OpenWRT community that could edit the page to add the tty event, that would be helpful to others. https://openwrt.org/docs/guide-user/base-system/hotplug#how_it_works

@galenseitz
ad 1: I intended the names to be persistent to the device and to path, and close to udev - but not exact. I'm not that pedantic. Getting that done exactly as in udev would probably take more code and effort - I'd like to keep this as simple as possible. Perhaps this can be extended inside hotplugd as new environment variables. Aand then used in the script. An idea worth exploring. Variables inside usb subsystem seem to cover that already.
As for mangling characters, I already excluded . and : from by-path symlinks, now I see a point to not mangle them for by-id as well.

ad 2: yeah, that's possible, but I'm unsure if it worked back in the 19.07 days, when I implemented this initially. I'd be welcome if you could try it out. "bind" would be good for coldplug, but as we're dealing with USB anyway, this doesn't matter as much, handling "add" events should work just as fine - and platform serial ports should be deterministic without that anyway.

ad 3: Wiki is often outdated. I can't promise to clean that up, but if you'd like, you can request a wiki account on forum.openwrt.org and document that, since you're fresh on the topic.

I understand about wanting to keep it simple. That said, I decided to go ahead and make the changes for myself. I forked your code. Unfortunately it seems that github doesn't support pull requests for gists. Anyway, you can see my version here https://gist.github.com/galenseitz/f3b2c4a45557eebe992dc637a1db070b. I have comments on each commit, but I don't see a way to view them. It looks like you may have to clone my gist to see them.

Copying the URL manually worked. It isn't as complicated as I envisioned after all, I'll try it out. Looks cool!
I plan to package the script in https://github.com/Leo-PL/my-openwrt-packages soon-ish. I mean - I created the package, but I have yet to at least build-test it.

@galenseitz I updated the wiki for TTY events as well, and hell - even put the script above as an example, already in your improved form.

Hi. Thank you for the script. I have an issue. My ch341 UART converter is not triggering an event in hotplug.d. Can you please help me to troubleshoot this issue?

As mentioned in wiki, I have created a file /etc/hotplug.d/tty/99-logger as mentioned in openwrt wiki with

logger -t hotplug $(env)

output of logread -e hotplug which does not contain my device ttyUSB0

root@OpenWrt:/# logread -e hotplug
Tue May 21 07:32:31 2024 user.notice hotplug: USER=root ACTION=add SHLVL=1 HOME=/ SEQNUM=513 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.4/ttyUSB3 LOGNAME=root DEVICENAME=ttyUSB3 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin PWD=/
Tue May 21 07:32:31 2024 user.notice hotplug: DEVNAME=ttyUSB3 USER=root ACTION=add SHLVL=1 HOME=/ SEQNUM=514 MAJOR=188 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.4/ttyUSB3/tty/ttyUSB3 LOGNAME=root DEVICENAME=ttyUSB3 TERM=linux SUBSYSTEM=tty PATH=/usr/sbin:/usr/bin:/sbin:/bin MINOR=3 PWD=/
Tue May 21 07:32:31 2024 user.notice hotplug: USER=root ACTION=bind SHLVL=1 HOME=/ SEQNUM=515 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.4/ttyUSB3 LOGNAME=root DEVICENAME=ttyUSB3 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin DRIVER=option1 PWD=/
Tue May 21 07:32:32 2024 user.notice hotplug: USER=root ACTION=add SHLVL=1 HOME=/ SEQNUM=517 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.5/ttyUSB4 LOGNAME=root DEVICENAME=ttyUSB4 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin PWD=/
Tue May 21 07:32:32 2024 user.notice hotplug: DEVNAME=ttyUSB4 USER=root ACTION=add SHLVL=1 HOME=/ SEQNUM=518 MAJOR=188 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.5/ttyUSB4/tty/ttyUSB4 LOGNAME=root DEVICENAME=ttyUSB4 TERM=linux SUBSYSTEM=tty PATH=/usr/sbin:/usr/bin:/sbin:/bin MINOR=4 PWD=/
Tue May 21 07:32:33 2024 user.notice hotplug: USER=root ACTION=bind SHLVL=1 HOME=/ SEQNUM=519 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.5/ttyUSB4 LOGNAME=root DEVICENAME=ttyUSB4 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin DRIVER=option1 PWD=/
Tue May 21 07:32:33 2024 user.notice hotplug: USER=root ACTION=add SHLVL=1 HOME=/ SEQNUM=521 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.6/ttyUSB5 LOGNAME=root DEVICENAME=ttyUSB5 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin PWD=/
Tue May 21 07:32:33 2024 user.notice hotplug: DEVNAME=ttyUSB5 USER=root ACTION=add SHLVL=1 HOME=/ SEQNUM=522 MAJOR=188 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.6/ttyUSB5/tty/ttyUSB5 LOGNAME=root DEVICENAME=ttyUSB5 TERM=linux SUBSYSTEM=tty PATH=/usr/sbin:/usr/bin:/sbin:/bin MINOR=5 PWD=/
Tue May 21 07:32:34 2024 user.notice hotplug: USER=root ACTION=bind SHLVL=1 HOME=/ SEQNUM=523 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.6/ttyUSB5 LOGNAME=root DEVICENAME=ttyUSB5 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin DRIVER=option1 PWD=/
Tue May 21 07:32:34 2024 user.notice hotplug: USER=root ACTION=add SHLVL=1 HOME=/ SEQNUM=525 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.7/ttyUSB6 LOGNAME=root DEVICENAME=ttyUSB6 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin PWD=/
Tue May 21 07:32:34 2024 user.notice hotplug: DEVNAME=ttyUSB6 USER=root ACTION=add SHLVL=1 HOME=/ SEQNUM=526 MAJOR=188 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.7/ttyUSB6/tty/ttyUSB6 LOGNAME=root DEVICENAME=ttyUSB6 TERM=linux SUBSYSTEM=tty PATH=/usr/sbin:/usr/bin:/sbin:/bin MINOR=6 PWD=/
Tue May 21 07:32:35 2024 user.notice hotplug: USER=root ACTION=bind SHLVL=1 HOME=/ SEQNUM=527 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.7/ttyUSB6 LOGNAME=root DEVICENAME=ttyUSB6 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin DRIVER=option1 PWD=/
Tue May 21 07:32:35 2024 user.notice hotplug: USER=root ACTION=add SHLVL=1 HOME=/ SEQNUM=529 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.8/ttyUSB7 LOGNAME=root DEVICENAME=ttyUSB7 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin PWD=/
Tue May 21 07:32:35 2024 user.notice hotplug: DEVNAME=ttyUSB7 USER=root ACTION=add SHLVL=1 HOME=/ SEQNUM=530 MAJOR=188 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.8/ttyUSB7/tty/ttyUSB7 LOGNAME=root DEVICENAME=ttyUSB7 TERM=linux SUBSYSTEM=tty PATH=/usr/sbin:/usr/bin:/sbin:/bin MINOR=7 PWD=/
Tue May 21 07:32:36 2024 user.notice hotplug: USER=root ACTION=bind SHLVL=1 HOME=/ SEQNUM=531 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.8/ttyUSB7 LOGNAME=root DEVICENAME=ttyUSB7 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin DRIVER=option1 PWD=/

dmesg output

[   11.279005] usb 1-1.1: ch341-uart converter now attached to ttyUSB0
[   11.752141] mt76_wmac 10300000.wmac: ASIC revision: 76280001
[   12.820404] mt76_wmac 10300000.wmac: Firmware Version: 20151201
[   12.826451] mt76_wmac 10300000.wmac: Build Time: 20151201183641
[   12.868042] mt76_wmac 10300000.wmac: firmware init done
[   13.344992] usbcore: registered new interface driver pl2303
[   13.350870] usbserial: USB Serial support registered for pl2303
[   13.421730] PPP generic driver version 2.4.2
[   13.449429] NET: Registered PF_PPPOX protocol family
[   13.505415] usbcore: registered new interface driver option
[   13.511305] usbserial: USB Serial support registered for GSM modem (1-port)
[   13.519259] option 1-1.2:1.2: GSM modem (1-port) converter detected
[   13.526040] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB1
[   13.533575] option 1-1.2:1.3: GSM modem (1-port) converter detected
[   13.540443] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB2
[   13.547894] option 1-1.2:1.4: GSM modem (1-port) converter detected
[   13.554751] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB3
[   13.562273] option 1-1.2:1.5: GSM modem (1-port) converter detected
[   13.569142] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB4
[   13.576643] option 1-1.2:1.6: GSM modem (1-port) converter detected
[   13.583542] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB5
[   13.591133] option 1-1.2:1.7: GSM modem (1-port) converter detected
[   13.597890] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB6
[   13.605524] option 1-1.2:1.8: GSM modem (1-port) converter detected
[   13.612398] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB7

ttyUSB1 also not triggering the event

root@OpenWrt:/# logread |grep USB0
Tue May 21 07:51:59 2024 kern.info kernel: [   11.309613] usb 1-1.1: ch341-uart converter now attached to ttyUSB0
root@OpenWrt:/# logread |grep USB1
Tue May 21 07:51:59 2024 kern.info kernel: [   13.568606] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB1
root@OpenWrt:/# logread |grep USB2
Tue May 21 07:51:59 2024 kern.info kernel: [   13.582983] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB2
Tue May 21 07:51:59 2024 user.notice hotplug: USER=root ACTION=bind SHLVL=1 HOME=/ SEQNUM=511 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.3/ttyUSB2 LOGNAME=root DEVICENAME=ttyUSB2 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin DRIVER=option1 PWD=/
root@OpenWrt:/# logread |grep USB3
Tue May 21 07:51:59 2024 kern.info kernel: [   13.597271] usb 1-1.2: GSM modem (1-port) converter now attached to ttyUSB3
Tue May 21 07:52:00 2024 user.notice hotplug: USER=root ACTION=add SHLVL=1 HOME=/ SEQNUM=513 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.4/ttyUSB3 LOGNAME=root DEVICENAME=ttyUSB3 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin PWD=/
Tue May 21 07:52:00 2024 user.notice hotplug: DEVNAME=ttyUSB3 USER=root ACTION=add SHLVL=1 HOME=/ SEQNUM=514 MAJOR=188 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.4/ttyUSB3/tty/ttyUSB3 LOGNAME=root DEVICENAME=ttyUSB3 TERM=linux SUBSYSTEM=tty PATH=/usr/sbin:/usr/bin:/sbin:/bin MINOR=3 PWD=/
Tue May 21 07:52:01 2024 user.notice hotplug: USER=root ACTION=bind SHLVL=1 HOME=/ SEQNUM=515 HOTPLUG_TYPE=tty DEVPATH=/devices/platform/101c0000.ehci/usb1/1-1/1-1.2/1-1.2:1.4/ttyUSB3 LOGNAME=root DEVICENAME=ttyUSB3 TERM=linux SUBSYSTEM=usb-serial PATH=/usr/sbin:/usr/bin:/sbin:/bin DRIVER=option1 PWD=/

Do you have links under /dev/serial/by-path? Symlinks for by-id won't work with CH340, because it lacks iSerialNumber attribute in USB descriptor. Also it's possible there is some copy-paste error, check if you can execute the script manually by passing required environment variables. Run set -x to enable shell debug.

@naseef Also use the version from the linked repository. One posted here is deprecated.

Seems like I have narrowed down the issue. The devices are directly soldered in to the board and not hotplugged, so openwrt won't initiate any hotplug events. I am still new this, correct me if I am wrong

And yes, I was using the code from the linked repo.

Still, bind events should work for coldplugged devices. Unless there is a bug in hotplugd which prevents this somehow.