Hi guys , i just wanted to take a look inside special devices in the linux kernel , especially the . loopback It’s a that comes with the , as we talked in previous articles ( ) the network stack refers to “ ” . To recap every time we create a new network namespace we are instantiating a struct net . virtual device network stack https://medium.com/@garciaj.uk/the-network-stack-153c92e35b26 struct net So that’s the first step , the second step is that the device is implemented as a driver as far as i can see , so most of its methods are implemented in . loopback https://github.com/torvalds/linux/blob/master/drivers/net/loopback.c So let’s take a look at the transmit function: , will be used to save stats as the name implies RX TX packets etc lb_stats will be used to store the length of the sk_buff ( ) len skb it’s used for “refcounting” , krefs or refcounting is a kernel design pattern where a counter is incremented by 1 when some method references it , and decremented when he reference is released , to then free() the object. skb_dst_force Used to determine the packet protocol id and insert it back in skb-> protocol eth_type_trans , this one is a complex one , this_cpu functions are mostly used to guarantee atomicity at the cpu level , that is to avoid the taxes to cpu switching etc (I might be totally wrong in this) this_cpu_ptr , receive method, called by driver when received on if; enqueues skb on the receiving queue and update stats etc , it returns a boolean that guarantee the reception of the frame( ). netif_rx skb skb In the next article I would like to investigate how packets and frames look in the kernel , we have talked about ( ) before so that’s the clue really. Let me know if you’d like to investigate other parts but I think it’s important to learn as much as we can about namepsaces and kernel isolation due to the popularity of containers etc. sk_buffs skb What you think?

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