How to enable debug logging for GRE?
How to enable debug logging for module ip_gre on linux 2.6?
Solution 1:
It looks like there is no output generated in ip_gre.c, except for
printk(KERN_INFO "GRE over IPv4 tunneling driver\n");
printk(KERN_INFO "ipgre init: can't add protocol\n");
and
printk(KERN_INFO "ipgre close: can't remove protocol\n");
So I'm afraid you're out of luck..