BUG: config_load之后，调用uci delete或者uci set xxx.xxx.xxx=''，再度掉用config_load，之后通过config_get读取出来的值将会出错,delete之后不使用commit
解决方法1：使用API函数config_unset或者config_set
解决方法2：
config_clear() {
local SECTION="$1"
#遍历每一项option,并将其unset
for oldvar in `set | grep ^CONFIG_${SECTION:+${SECTION}_} | \
sed -e 's/\(.*\)=.*$/\1/'` ; do
unset $oldvar
done
}
config () {
local cfgtype="$1"
local name="$2"
config_clear $name
export ${NO_EXPORT:+-n} CONFIG_NUM_SECTIONS=$(($CONFIG_NUM_SECTIONS + 1))
name="${name:-cfg$CONFIG_NUM_SECTIONS}"
append CONFIG_SECTIONS "$name"
[ -n "$NO_CALLBACK" ] || config_cb "$cfgtype" "$name"
export ${NO_EXPORT:+-n} CONFIG_SECTION="$name"
export ${NO_EXPORT:+-n} "CONFIG_${CONFIG_SECTION}_TYPE=$cfgtype"
}
在调用api时，首先我们需要调用config_load
config_load() {
[ -n "$IPKG_INSTROOT" ] && return 0
uci_load "$@"
}
uci_load() {
local PACKAGE="$1"
local DATA
local RET
local VAR
_C=0
if [ -z "$CONFIG_APPEND" ]; then
for VAR in $CONFIG_LIST_STATE; do
export ${NO_EXPORT:+-n} CONFIG_${VAR}=
export ${NO_EXPORT:+-n} CONFIG_${VAR}_LENGTH=
done
export ${NO_EXPORT:+-n} CONFIG_LIST_STATE=
export ${NO_EXPORT:+-n} CONFIG_SECTIONS=
export ${NO_EXPORT:+-n} CONFIG_NUM_SECTIONS=0
export ${NO_EXPORT:+-n} CONFIG_SECTION=
fi
DATA="$(/sbin/uci ${UCI_CONFIG_DIR:+-c $UCI_CONFIG_DIR} ${LOAD_STATE:+-P /var/state} -S -n export "$PACKAGE" 2>/dev/null)"
RET="$?"
[ "$RET" != 0 -o -z "$DATA" ] || eval "$DATA"
unset DATA
${CONFIG_SECTION:+config_cb}
return "$RET"
}
1、首先通过uci export $PACKAGE 获取配置文件的内容（其他参数就不一一简绍了，具体查看uci --help）
package xxx
config xxx xxx
option xxx xxx
list xxx xxx
2、之后eval "$DATA"，将package config option替换成函数（这一步是很让我很惊艳的用法，得向大牛学习）
package() {
return 0
}
config () {
local cfgtype="$1"
local name="$2"
export ${NO_EXPORT:+-n} CONFIG_NUM_SECTIONS=$(($CONFIG_NUM_SECTIONS + 1))
name="${name:-cfg$CONFIG_NUM_SECTIONS}"
append CONFIG_SECTIONS "$name"
[ -n "$NO_CALLBACK" ] || config_cb "$cfgtype" "$name"
export ${NO_EXPORT:+-n} CONFIG_SECTION="$name"
export ${NO_EXPORT:+-n} "CONFIG_${CONFIG_SECTION}_TYPE=$cfgtype"
}
option () {
local varname="$1"; shift
local value="$*"
export ${NO_EXPORT:+-n} "CONFIG_${CONFIG_SECTION}_${varname}=$value"
[ -n "$NO_CALLBACK" ] || option_cb "$varname" "$*"
}
list() {
local varname="$1"; shift
local value="$*"
local len
config_get len "$CONFIG_SECTION" "${varname}_LENGTH" 0
[ $len = 0 ] && append CONFIG_LIST_STATE "${CONFIG_SECTION}_${varname}"
len=$(($len + 1))
config_set "$CONFIG_SECTION" "${varname}_ITEM$len" "$value"
config_set "$CONFIG_SECTION" "${varname}_LENGTH" "$len"
append "CONFIG_${CONFIG_SECTION}_${varname}" "$value" "$LIST_SEP"
list_cb "$varname" "$*"
}
3、通过这四个函数将每一项配置项设置到环境变量当中
（bug出现原因：当设入环境变量后，通过uci delete或uci set 删除只会操作换存，在调用config_load 因为option项不存在了，则不会在度设置到环境变量中，因此还是删除之前的值，而不是空）
4、之后的config_get之类的函数就是获取环境变量的值
for oldvar in `set | grep ^CONFIG_${SECTION:+${SECTION}_} | \
sed -e 's/\(.*\)=.*$/\1/'` ; do
for oldvar in `set | grep ^CONFIG_${SECTION:+${SECTION}_} | \
sed -e 's/\(.*\)=.*$/\1/'` ; do
for oldvar in `set | grep ^CONFIG_${SECTION:+${SECTION}_} | \
sed -e 's/\(.*\)=.*$/\1/'` ; do
for oldvar in `set | grep ^CONFIG_${SECTION:+${SECTION}_} | \
sed -e 's/\(.*\)=.*$/\1/'` ; do
for oldvar in `set | grep ^CONFIG_${SECTION:+${SECTION}_} | \
sed -e 's/\(.*\)=.*$/\1/'` ; do
for oldvar in `set | grep ^CONFIG_${SECTION:+${SECTION}_} | \
sed -e 's/\(.*\)=.*$/\1/'` ; do
