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bpf, doc: Add heading and example for extensions in cbpf 

Add new heading for extensions to make it more readable. Also, add one
more example of filtering interface index for better understanding.

Signed-off-by: Roy, UjjaL <royujjal@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/CAADnVQJ=DoRDcVkaXmY3EmNdLoO7gq1mkJOn5G=00wKH8qUtZQ@mail.gmail.com
This commit is contained in:
Roy, UjjaL 2021-07-16 22:04:41 +02:00 committed by Daniel Borkmann
parent c7603cfa04
commit 8886534747
1 changed files with 16 additions and 7 deletions
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23
Documentation/networking/filter.rst
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@ -320,13 +320,6 @@ Examples for low-level BPF:
ret #-1
drop: ret #0
**(Accelerated) VLAN w/ id 10**::
ld vlan_tci
jneq #10, drop
ret #-1
drop: ret #0
**icmp random packet sampling, 1 in 4**::
ldh [12]
@ -358,6 +351,22 @@ Examples for low-level BPF:
bad: ret #0 /* SECCOMP_RET_KILL_THREAD */
good: ret #0x7fff0000 /* SECCOMP_RET_ALLOW */
Examples for low-level BPF extension:
**Packet for interface index 13**::
ld ifidx
jneq #13, drop
ret #-1
drop: ret #0
**(Accelerated) VLAN w/ id 10**::
ld vlan_tci
jneq #10, drop
ret #-1
drop: ret #0
The above example code can be placed into a file (here called "foo"), and
then be passed to the bpf_asm tool for generating opcodes, output that xt_bpf
and cls_bpf understands and can directly be loaded with. Example with above