xref: /src/share/examples/devpubd/hooks/99-ucom-symlinks

#!/bin/sh -
#
# $NetBSD: 99-ucom-symlinks,v 1.1 2024/03/30 06:29:01 thorpej Exp $
#
# Attempt to create stable names (using symbolic links) to USB serial
# devices, regardless of device enumeration order, suitable for use in
# configuration files.  The format of the stable names is:
#
#	/dev/{cdt}ty-$driver-$serialnumber-$portnumber
# - or -
#	/dev/{cdt}ty-$driver-$serialnumber
#
# depending on whether or not the device is a multi-port adapter.
#
# e.g.
#
#	/dev/tty-uftdi-FT64S4YP-1 -> /dev/ttyU0
#
#	/dev/tty-uslsa-01E7ABCC -> /dev/ttyU4
#
# If $driver or $serialnumber cannot be determined, then no symbolic link
# will be created.
#
# Written by Jason R. Thorpe, December 2022.  Public domain.
#

export LC_ALL=C

event="$1"
shift
devices=$@

symlink_name()
{
	local parent
	local portnum
	local serialnum
	local driver

	parent=$(drvctl -p $1 device-parent)
	if [ x"$parent" != x ]; then
		driver=$(drvctl -p $parent device-driver)
		serialnum=$(drvctl -p $parent serialnumber)
	fi

	# If the device is a single-port device, it may have the default
	# port number locator of '-1'.  In that case, elide the port
	# number.
	portnum=$(drvctl -p $1 port)
	if [ x"$portnum" = x"-1" -o x"$portnum" = x ]; then
		portnum=""
	else
		portnum="-${portnum}"
	fi

	if [ x"$driver" != x -a x"$serialnum" != x ]; then
		echo "${driver}-${serialnum}${portnum}"
	else
		echo ""
	fi
}

remove_ucom_symlink()
{
	local name
	local unit

	name=$(readlink "/dev/${1}")

	if [ x"$name" != x ]; then
		rm -f "/dev/tty-${name}"
		rm -f "/dev/dty-${name}"
		rm -f "/dev/cty-${name}"
		rm -f "/dev/${1}"
	fi
}

add_ucom_symlink()
{
	local name
	local tty_path
	local dty_path
	local cty_path

	name=$(symlink_name $1)
	unit=$(drvctl -p $1 device-unit)

	if [ x"$name" != x -a x"$unit" != x ]; then
		#
		# We need to make two sets of symlinks:
		#
		# /dev/tty-uslsa-01E7ABCC -> /dev/ttyU4
		#
		# /dev/ucom4 -> uslsa-01E7ABCC
		#
		# This is needed because when we get the detach event
		# for e.g. ucom4, the parent device (e.g. uslsa0) may
		# already be gone, meaning we cannot query it.  So
		# what we're doing is stashing the information in the
		# second symlink so we can readlink(1) it later to
		# recover the stable name.
		#

		tty_path="/dev/ttyU${unit}"
		dty_path="/dev/dtyU${unit}"
		cty_path="/dev/ctyU${unit}"

		ln -sf "${name}" "/dev/${1}"
		if [ -c ${tty_path} ]; then
			ln -sf ${tty_path} "/dev/tty-${name}"
		fi
		if [ -c ${dty_path} ]; then
			ln -sf ${dty_path} "/dev/dty-${name}"
		fi
		if [ -c ${cty_path} ]; then
			ln -sf ${cty_path} "/dev/cty-${name}"
		fi
	fi
}

for device in $devices; do
	case $device in
	ucom*)
		case $event in
		device-attach)
			remove_ucom_symlink $device
			add_ucom_symlink $device
			;;
		device-detach)
			remove_ucom_symlink $device
			;;
		esac
	esac
done