book@ubuntu:/work/project/wifi/04.hostapd/hostapd-2.0/hostapd$ make
/usr/bin/ld: cannot find -lnl
collect2: ld returned 1 exit status
make: *** [hostapd] Error 1
问题原因是，没有找到 nl 库 ！
然后我搜索 这个 nl 库是在哪儿被使用的：
book@ubuntu:/work/project/wifi/04.hostapd/hostapd-2.0$ grep "\-lnl" * -nR
src/drivers/drivers.mak:31: DRV_LIBS += -lnl-3
src/drivers/drivers.mak:32: DRV_LIBS += -lnl-genl-3
src/drivers/drivers.mak:36: DRV_LIBS += -lnl-tiny
src/drivers/drivers.mak:38: DRV_LIBS += -lnl
src/drivers/drivers.mak:42: DRV_LIBS += -lnl-genl
src/drivers/drivers.mak:148: DRV_LIBS += -lnl-3
src/drivers/drivers.mak:149: DRV_LIBS += -lnl-genl-3
src/drivers/drivers.mak:150: DRV_LIBS += -lnl-route-3
src/drivers/drivers.mak:154: DRV_LIBS += -lnl-tiny
src/drivers/drivers.mak:156: DRV_LIBS += -lnl
src/drivers/drivers.mak:160: DRV_LIBS += -lnl-genl
src/drivers/drivers.mak:161: DRV_LIBS += -lnl-route
src/drivers/drivers.mk:31: DRV_LIBS += -lnl-3
src/drivers/drivers.mk:32: DRV_LIBS += -lnl-genl-3
src/drivers/drivers.mk:36: DRV_LIBS += -lnl-tiny
src/drivers/drivers.mk:38: DRV_LIBS += -lnl
src/drivers/drivers.mk:42: DRV_LIBS += -lnl-genl
src/drivers/drivers.mk:152: DRV_LIBS += -lnl-3
src/drivers/drivers.mk:153: DRV_LIBS += -lnl-genl-3
src/drivers/drivers.mk:154: DRV_LIBS += -lnl-route-3
src/drivers/drivers.mk:158: DRV_LIBS += -lnl-tiny
src/drivers/drivers.mk:160: DRV_LIBS += -lnl
src/drivers/drivers.mk:164: DRV_LIBS += -lnl-genl
src/drivers/drivers.mk:165: DRV_LIBS += -lnl-route
然后，我们查看交叉编译库里 有没有 nl 的库
/usr/local/arm/4.3.2/arm-none-linux-gnueabi/libc/armv4t/lib
然后，发现里面有这个库。
book@ubuntu:/work/project/wifi/04.hostapd/hostapd-2.0$ ls /usr/local/arm/4.3.2/arm-none-linux-gnueabi/libc/armv4t/lib
engines libnl libnsl.so.1
jconfig.h libnl-3.a libnss_compat-2.8.so
jerror.h libnl-3.la libnss_compat.so.2
jmorecfg.h libnl-3.so libnss_dns-2.8.so
jpeglib.h libnl-3.so.200 libnss_dns.so.2
ld-2.8.so libnl-3.so.200.18.0 libnss_files-2.8.so
ld-linux.so.3 libnl-cli-3.a libnss_files.so.2
libanl-2.8.so libnl-cli-3.la libnss_hesiod-2.8.so
libanl.so.1 libnl-cli-3.so libnss_hesiod.so.2
libBrokenLocale-2.8.so libnl-cli-3.so.200 libnss_nis-2.8.so
libBrokenLocale.so.1 libnl-cli-3.so.200.18.0 libnss_nisplus-2.8.so
libc-2.8.so libnl-genl-3.a libnss_nisplus.so.2
libcidn-2.8.so libnl-genl-3.la libnss_nis.so.2
libcidn.so.1 libnl-genl-3.so libpcprofile.so
libcrypt-2.8.so libnl-genl-3.so.200 libpthread-2.8.so
libcrypto.a libnl-genl-3.so.200.18.0 libpthread.so.0
libcrypto.so libnl-idiag-3.a libresolv-2.8.so
libcrypto.so.1.0.0 libnl-idiag-3.la libresolv.so.2
libcrypt.so.1 libnl-idiag-3.so librt-2.8.so
libc.so.6 libnl-idiag-3.so.200 librt.so.1
libdl-2.8.so libnl-idiag-3.so.200.18.0 libSegFault.so
libdl.so.2 libnl-nf-3.a libssl.a
libfreetype.a libnl-nf-3.la libssl.so
libfreetype.la libnl-nf-3.so libssl.so.1.0.0
libfreetype.so libnl-nf-3.so.200 libthread_db-1.0.so
libfreetype.so.6 libnl-nf-3.so.200.18.0 libthread_db.so.1
libfreetype.so.6.9.0 libnl-route-3.a libutil-2.8.so
libgcc_s.so libnl-route-3.la libutil.so.1
libgcc_s.so.1 libnl-route-3.so libz.a
libm-2.8.so libnl-route-3.so.200 pkgconfig
libmemusage.so libnl-route-3.so.200.18.0 turbojpeg.h
libm.so.6 libnsl-2.8.so
那么原因就出在 src/drivers/drivers.mak 里了！ 肯定是编译时，-lnl-3 库没有包含进来。
然后，打开这个文件。
vi src/drivers/drivers.mk +31
发现下面这几句。
ifdef CONFIG_LIBNL32
DRV_LIBS += -lnl-3
DRV_LIBS += -lnl-genl-3
DRV_CFLAGS += -DCONFIG_LIBNL20 -I/usr/include/libnl3
那么我们只需要，在配置文件.config里，加 CONFIG_LIBNL32 = y 就可以了。