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

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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