hid-rebind

#!/bin/sh
#
# Rebind HID device to specific driver.
# Author: Nikolai Kondrashov <spbnick@gmail.com>
#
# To be used with udev rules like this one:
# SUBSYSTEM=="hid", ACTION=="add", ENV{HID_ID}=="0003:0000172F:*", \
#     RUN+="/usr/local/bin/hid-rebind" 
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#

set -e -u

progname=`basename "$0"`

# Write a string to a file, ignoring ENODEV.
write_ignore_enodev() {
    local str="$1"
    local path="$2"
    local output

    # Write the string with tee, capturing error output
    if ! output=`echo "$str" | tee "$path" 2>&1 >/dev/null`; then
        # Raise anything except ENODEV
        if test "${output##*: }" != "No such device"; then
            echo "$output" >&2
            return 1
        fi
    fi
}

{
    id=`basename "$DEVPATH"`

    cur_driver_path=`readlink -v -f "/sys${DEVPATH}/driver"`
    if test -e "$cur_driver_path"; then
        cur_driver=`basename "$cur_driver_path"`
    else
        cur_driver=""
    fi

    # Choose a matching module installed under .../extra/
    new_module=$(
        modprobe -R "$MODALIAS" | tr - _ |
            while read -r m; do
                if modinfo -F filename "$m" | grep -q /extra/; then
                    echo "$m"
                    break
                fi
            done
    )
    if test -z "$new_module"; then
        exit 0
    fi
    # Assume the driver will be called the same as module,
    # but without the "hid_" prefix
    new_driver="${new_module#hid_}"
    new_driver_path="/sys/bus/hid/drivers/$new_driver"

    if test "$new_driver" = "$cur_driver"; then
        exit 0
    fi

    logger -p daemon.notice -t "$progname" \
           "rebinding $DEVPATH to \"$new_driver\" driver"

    # Ensure the new driver module is loaded
    modprobe "$new_module"

    # Unbind from the current driver, if any
    if test -e "$cur_driver_path"; then
        write_ignore_enodev "$id" "$cur_driver_path/unbind"
    fi

    # Bind to the new driver
    write_ignore_enodev "$id" "$new_driver_path/bind"
} 2>&1 | logger -p daemon.warning -t "$progname"