RTNETLINK answers: File exists问题分析
最近在调试以太网时一直出现“RTNETLINK answers: File exists”错误，刚开始一直以为是以太网驱动的问题，以太网采用的是MII接口，phy采用的YT8522，很奇怪的是出现上述错误时，以太网其实工作是正常的。另外一路采用RMII，同样的phy芯片的却没有报这个错误，百思不得其解。
root@test:~# ifup -a
[ 26.985738] mac030 54200000.gmac eth0: Link is Down
[ 27.193736] mac030 54300000.gmac eth1: Link is Down
RTNETLINK answers: File exists
Failed to bring up eth1.手动单个以太网去配置时，发现每次都是第一个配置的成功，第二个配置的就报上述的错误，如下，先配置eth1，再配置eth0，则eth0配置时报错。
root@test:~# ifup eth1
[ 24.163714] gmac030 54300000.gmac eth1: Link is Down
root@test:~#
root@test:~#
root@test:~# ifup eth0
[ 27.285840] mac030 54200000.gmac eth0: Link is Down
RTNETLINK answers: File exists
Failed to bring up eth0.也就是说谁先配置谁成功，后配置则失败，那么原因究竟是啥呢，网上搜索了好久也没有找到原因，既然这样就直接看ifup的源代码吧，在代码中加上一些打印看看。操作如下：
root@test:~# ./ifup eth0
===== do_interface 1 =====
===== lock_interface 1 filename is /run/network/ifstate.eth0 =====
===== lock_interface 3 =====
===== lock_interface 4 =====
===== lock_interface 6 =====
===== lock_interface 7 =====
===== lock_interface 8 =====
===== do_interface 2 current_state is 0 =====
##### out is #####
===== Configuring interface eth0=eth0 (inet) ======
===== do_interface 3 pidfilename is /run/network/ifup-eth0.pid =====
===== do_interface 4 command is ifup =====
===== do_interface 5 no_act is 0 =====
===== do_interface 6 =====
####### inet _static_up 1 #######
##### out is /sbin/ip addr add 192.168.2.170/255.255.255.0 broadcast 192.168.2.255 dev eth0 label eth0 #####
####### inet _static_up 2 #######
##### out is /sbin/ip link set dev eth0 up #####
####### inet _static_up 3 #######
##### out is /sbin/ip route add default via 192.168.2.254 dev eth0 onlink #####
####### inet _static_up 4 #######
===== iface_up 1 result is 1 =====
===== iface_up 2 =====
===== iface_postup 1 =====
===== iface_postup method name is static =====
####### inet _static_up 1 #######
##### out is /sbin/ip addr add 192.168.2.170/255.255.255.0 broadcast 192.168.2.255 dev eth0 label eth0 #####
####### inet _static_up 2 #######
##### out is /sbin/ip link set dev eth0 up #####
####### inet _static_up 3 #######
[ 128.882457] mac030 54200000.gmac eth0: Link is Down
##### out is /sbin/ip route add default via 192.168.2.254 dev eth0 onlink #####
####### inet _static_up 4 #######
===== iface_postup 5 =====
===== current_state is 0 failed is 0 =====先操作eth0成功，接下来操作eth1
root@test:~# ./ifup eth1
===== do_interface 1 =====
===== lock_interface 1 filename is /run/network/ifstate.eth1 =====
===== lock_interface 3 =====
===== lock_interface 4 =====
===== lock_interface 6 =====
===== lock_interface 7 =====
===== lock_interface 8 =====
===== do_interface 2 current_state is 0 =====
##### out is #####
===== Configuring interface eth1=eth1 (inet) ======
===== do_interface 3 pidfilename is /run/network/ifup-eth1.pid =====
===== do_interface 4 command is ifup =====
===== do_interface 5 no_act is 0 =====
===== do_interface 6 =====
####### inet _static_up 1 #######
##### out is /sbin/ip addr add 192.168.1.170/255.255.252.0 broadcast 192.168.3.255 dev eth1 label eth1 #####
####### inet _static_up 2 #######
##### out is /sbin/ip link set dev eth1 up #####
####### inet _static_up 3 #######
##### out is /sbin/ip route add default via 192.168.1.254 dev eth1 onlink #####
####### inet _static_up 4 #######
===== iface_up 1 result is 1 =====
===== iface_up 2 =====
===== iface_postup 1 =====
===== iface_postup method name is static =====
####### inet _static_up 1 #######
##### out is /sbin/ip addr add 192.168.1.170/255.255.252.0 broadcast 192.168.3.255 dev eth1 label eth1 #####
####### inet _static_up 2 #######
##### out is /sbin/ip link set dev eth1 up #####
####### inet _static_up 3 #######
[ 230.948350] mac030 54300000.gmac eth1: Link is Down
RTNETLINK answers: File exists
##### out is /sbin/ip route add default via 192.168.1.254 dev eth1 onlink #####
===== iface_postup 2 =====
===== 2 failed is 1 =====
===== current_state is 0 failed is 1 =====
Failed to bring up eth1.
root@test:~# 问题出来了，执行"/sbin/ip route add default via 192.168.1.254 dev eth1 onlink"失败了,打开eth1的network配置文件如下：
#iface eth1 inet manual
auto eth1
#allow-hotplug eth1
iface eth1 inet static
address 192.168.1.170
netmask 255.255.255.0
gateway 192.168.1.254
dns-nameservers 192.168.1.240eth0如下：
#iface eth0 inet manual
auto eth0
#allow-hotplug eth0
iface eth0 inet static
address 192.168.2.170
netmask 255.255.255.0
gateway 192.168.2.254
dns-nameservers 192.168.2.240那问题就在gateway这句话了，两个配置文件中都有这个配置，将eth1中的gateway注释掉就OK了。