Two kernel modules, each using a netlink socket. How to use them at the same time?

Question

Good day. I would like to create two (almost identical) modules - each module uses a netlink socket and responds to an incoming message from a user space program.

During initialization of the first module, it successfully executes the following command:

netlink kernel create(&init_net, NETLINK_USER, &cfg) 

However, if I run the second module with the same arguments, the same command will cause an error.

I thought this error occurred because the NETLINK_USER value of both modules was the same - 31 - which is why I could not create a second socket connection for the same netlink user. However, if I try the NETLINK_USER value of 32, a kernel error will occur. Any other value is an error.

Please tell me what I need to do to use two kernel modules at the same time?

Answer 1

By default, the kernel has 32 network slots. Some of them are used by the system (for example, the audit subsystem). Here you can find information about predefined constants here . As for your question, try using the following:

 // module 1 netlink kernel create(&init_net, MAX_LINKS - 1, &cfg) // module 2 netlink kernel create(&init_net, MAX_LINKS - 2, &cfg) 

MAX_LINKS is the limit for network lines supported by the kernel.