Question

I am trying to have iptables-1.4.3.2 work with Linux-2.6.35.9 on our MIPS based platform. The command issued is

iptables -t mangle -A POSTROUTING -p udp -j <TC name> --map tos

iptables exits with input/output error (The same command was working on Linux-2.6.28.8). Then did a strace for the same on our target and seeing problem as below :

socket(PF_INET, SOCK_RAW, IPPROTO_RAW)  = 3
getsockopt(3, SOL_IP, 0x40 /* IP_??? */, "mangle\0\0\0\0\0\34\200F\0\0\200\1\340   \244\200\1\340\244\200\7W\224\200\7W\f\0"..., [84]) = 0
getsockopt(3, SOL_IP, 0x41 /* IP_??? */, "mangle\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., [976]) = 0
setsockopt(3, SOL_IP, 0x40 /* IP_??? */, "mangle\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1240) = -1 EIO (Input/output error)
close(3)                                = 0
write(2, "iptables: "..., 10iptables: )           = 10
write(2, "Input/output error"..., 18Input/output error)   = 18
write(2, ".\n"..., 2.
)                   = 2
munmap(0x2ab9b000, 75264)               = 0
exit(1)                                

The above code is in libiptc.c ; Any suggestions to debug the error further would be helpful. Thanks.

Answer 1

EIO means that your custom “TC” target (or whatever it is you meant by it) module, i.e. xt_TC.c, does not adhere to the API. checkentry is not supposed to return values greater than zero (there is no meaning assigned to them) in 2.6.35 and up.