LinuxQuestions.org - Why is there no function for packet reception in linux loopback network interface ?

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Why is there no function for packet reception in linux loopback network interface ?

Normally any network driver should provide a function or should implement an interrupt for the packet reception however /drivers/net/loopback.c which is the source code for linux network loopback interface does not contain any mechanism to implement packet reception.

How does it function without an exclusive reception mechanism?

Quote:

Originally Posted by avee137 (Post 4452849)

Where would it be receiving from? The loopback driver does not have any associated hardware; send and receive are the same thing.

Even though it does not have any h/w ,It sends packets to itself and that has to be received and sent up the protocol stack to the application layer. When we use ping we get reply as below:

Code:

avi@linux-inng:~/cscope> ping 127.0.0.1

PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data.

64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.043 ms

64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.039 ms

64 bytes from 127.0.0.1: icmp_seq=3 ttl=64 time=0.031 ms

64 bytes from 127.0.0.1: icmp_seq=4 ttl=64 time=0.048 ms

64 bytes from 127.0.0.1: icmp_seq=5 ttl=64 time=0.048 ms

64 bytes from 127.0.0.1: icmp_seq=6 ttl=64 time=0.051 ms

64 bytes from 127.0.0.1: icmp_seq=7 ttl=64 time=0.049 ms

64 bytes from 127.0.0.1: icmp_seq=8 ttl=64 time=0.040 ms

64 bytes from 127.0.0.1: icmp_seq=9 ttl=64 time=0.047 ms

64 bytes from 127.0.0.1: icmp_seq=10 ttl=64 time=0.048 ms

64 bytes from 127.0.0.1: icmp_seq=11 ttl=64 time=0.038 ms

64 bytes from 127.0.0.1: icmp_seq=12 ttl=64 time=0.049 ms

64 bytes from 127.0.0.1: icmp_seq=13 ttl=64 time=0.048 ms

64 bytes from 127.0.0.1: icmp_seq=14 ttl=64 time=0.039 ms

^C

--- 127.0.0.1 ping statistics ---

14 packets transmitted, 14 received, 0% packet loss, time 13000ms

rtt min/avg/max/mdev = 0.031/0.044/0.051/0.006 ms

Even though it does not have any h/w ,It sends packets to itself and that has to be received and sent up the protocol stack to the application layer. When we use ping we get reply as below:

Code:

avi@linux-inng:~/cscope> ping 127.0.0.1

PING 127.0.0.1 (127.0.0.1) 56(84) bytes of data.

64 bytes from 127.0.0.1: icmp_seq=1 ttl=64 time=0.043 ms

64 bytes from 127.0.0.1: icmp_seq=2 ttl=64 time=0.039 ms

64 bytes from 127.0.0.1: icmp_seq=3 ttl=64 time=0.031 ms

64 bytes from 127.0.0.1: icmp_seq=4 ttl=64 time=0.048 ms

64 bytes from 127.0.0.1: icmp_seq=5 ttl=64 time=0.048 ms

64 bytes from 127.0.0.1: icmp_seq=6 ttl=64 time=0.051 ms

64 bytes from 127.0.0.1: icmp_seq=7 ttl=64 time=0.049 ms

64 bytes from 127.0.0.1: icmp_seq=8 ttl=64 time=0.040 ms

64 bytes from 127.0.0.1: icmp_seq=9 ttl=64 time=0.047 ms

64 bytes from 127.0.0.1: icmp_seq=10 ttl=64 time=0.048 ms

64 bytes from 127.0.0.1: icmp_seq=11 ttl=64 time=0.038 ms

64 bytes from 127.0.0.1: icmp_seq=12 ttl=64 time=0.049 ms

64 bytes from 127.0.0.1: icmp_seq=13 ttl=64 time=0.048 ms

64 bytes from 127.0.0.1: icmp_seq=14 ttl=64 time=0.039 ms

^C

--- 127.0.0.1 ping statistics ---

14 packets transmitted, 14 received, 0% packet loss, time 13000ms

rtt min/avg/max/mdev = 0.031/0.044/0.051/0.006 ms

it clearly shows 14 packets transmitted, 14 received.

so there must be some exclusive mechanism at work. Which does not appear anywhere in cource code loopback.c .