编译hostapd时，出现错误：/usr/bin/ld: cannot find -lnl

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。