linux hotplug相关

chensg

相信这里一定有hotplug方面的专家，小弟请教一个问题：
最近在做多媒体播放器，嵌入linux系统（kernel2.6.5），带有USB主机的功能，希望在usb设备插入时，能自动mount到系统上。据了解，其/proc/sys/kernel/hotplug 指向 /sbin/hotplug 。

在阅读相应脚本的过程中，有个疑问一直想不明白，在脚本 hotplug.functions里，有个函数 load_drivers，如下，在红色部分，LISTER被赋为空，随后的 if 判断似乎永远不为真，是吗？
变量DRIVERS也为空，所以return走了，之后的操作就永远执行不到，对吗？
谢谢！
小弟在linux上才做了半年开发，懂得太少，如果愿意，请添加我的msn（dchen.cn@gmail.com ）, 我们可以直接交流。

load_drivers ()
{
    local LOADED TYPE FILENAME DESCRIPTION LISTER
    DRIVERS=""

    TYPE=$1
    FILENAME=$2
    DESCRIPTION=$3

    # should we use usbmodules, pcimodules?  not on 2.5+, because sysfs
    # ought to expose the data we need to find all candidate drivers.
    # (on 2.5.48 it does for usb; but maybe not yet for pci.)
   LISTER=""
    if [ "$LISTER" != "" ]; then
        case $TYPE in
        usb)
            if [ "$DEVICE" = "" -o ! -f "$DEVICE" ]; then
                LISTER=
            else
                DRIVERS=`$LISTER --mapfile $FILENAME --device $DEVICE`
            fi ;;

        pci)
            echo incasepci >> invoking-functions
            debug_mesg "pcimodules is scanning more than $PCI_SLOT ..."
            DRIVERS=`$LISTER`
            ;;
        esac
    fi

    # try parsing by shell scripts if no luck yet
    if [ "$DRIVERS" = "" ]; then
        ${TYPE}_map_modules < $FILENAME
    fi

    # FIXME remove dups and blacklisted modules from $DRIVERS here
    if [ "$DRIVERS" = "" ]; then
        return
    fi

    debug_mesg Setup $DRIVERS for $DESCRIPTION

    # either kernel or user mode drivers may need to be set up
    for MODULE in $DRIVERS
    do
        # maybe driver modules need loading
        LOADED=false
        if ! lsmod | grep -q "^$(echo $MODULE|sed -e 's/-/_/g') " > /dev/null 2>&1; then
            if grep -q "^$(echo $MODULE|sed -e 's/[-_]/[-_]/g')\$" $HOTPLUG_DIR/blacklist \
                        $HOTPLUG_DIR/blacklist.d/* \
                    >/dev/null 2>&1; then
                debug_mesg "... blacklisted module:  $MODULE"
                continue
            fi

            # statically linked modules aren't shown by 'lsmod',
            # and user mode drivers will ONLY have a setup script;
            # it's not an error if a module doesn't exist or won't load.
            if $MODPROBE -n $MODULE >/dev/null 2>&1 &&
                    ! $MODPROBE $MODULE >/dev/null 2>&1 ; then
                mesg "... can't load module $MODULE"
            else
                # /etc/modules.conf may have set non-default module
                # parameters ... handle per-device parameters in apps
                # (ioctls etc) not in setup scripts or modules.conf
                LOADED=true
            fi
        else
            # This module is already loaded
            LOADED=true
        fi

        # always run setup scripts after any matching kernel code has had
        # a chance to do its thing, no matter whether it was dynamically
        # or statically linked, or if there is only a user mode driver.
        # the script might re-enumerate usb devices after firmware download,
        # giving kernel code another chance.
        if [ -x $HOTPLUG_DIR/$TYPE/$MODULE ]; then
            debug_mesg Module setup $MODULE for $DESCRIPTION
            $HOTPLUG_DIR/$TYPE/$MODULE
            LOADED=true
        fi

        if [ "$LOADED" = "false" ]; then
            mesg "missing kernel or user mode driver $MODULE "
        fi
        if echo "$MODULE" | grep -q "usb-storage" > /dev/null 2>&1 ; then
            [ -x /usr/sbin/updfstab ] &&  /usr/sbin/updfstab
        fi
    done
}