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Commit bd0fb9d0 authored by Quentin Monnet's avatar Quentin Monnet Committed by Daniel Borkmann
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tools: bpftool: add a prog array map update example to documentation 



Add an example in map documentation to show how to use bpftool in order
to update the references to programs hold by prog array maps.

Signed-off-by: default avatarQuentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: default avatarJakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 32870ba4

tools/bpf/bpftool/Documentation/bpftool-map.rst

+55 −0
Original line number Diff line number Diff line
@@ -170,6 +170,61 @@ The following three commands are equivalent: 
| **# bpftool map pin id 10 /sys/fs/bpf/map**

| **# bpftool map del pinned /sys/fs/bpf/map key 13 00 07 00**



Note that map update can also be used in order to change the program references

hold by a program array map. This can be used, for example, to change the

programs used for tail-call jumps at runtime, without having to reload the

entry-point program. Below is an example for this use case: we load a program

defining a prog array map, and with a main function that contains a tail call

to other programs that can be used either to "process" packets or to "debug"

processing. Note that the prog array map MUST be pinned into the BPF virtual

file system for the map update to work successfully, as kernel flushes prog

array maps when they have no more references from user space (and the update

would be lost as soon as bpftool exits).



|

| **# bpftool prog loadall tail_calls.o /sys/fs/bpf/foo type xdp**

| **# bpftool prog --bpffs**



::



  545: xdp  name main_func  tag 674b4b5597193dc3  gpl

          loaded_at 2018-12-12T15:02:58+0000  uid 0

          xlated 240B  jited 257B  memlock 4096B  map_ids 294

          pinned /sys/fs/bpf/foo/xdp

  546: xdp  name bpf_func_process  tag e369a529024751fc  gpl

          loaded_at 2018-12-12T15:02:58+0000  uid 0

          xlated 200B  jited 164B  memlock 4096B

          pinned /sys/fs/bpf/foo/process

  547: xdp  name bpf_func_debug  tag 0b597868bc7f0976  gpl

          loaded_at 2018-12-12T15:02:58+0000  uid 0

          xlated 200B  jited 164B  memlock 4096B

          pinned /sys/fs/bpf/foo/debug



**# bpftool map**



::



  294: prog_array  name jmp_table  flags 0x0

          key 4B  value 4B  max_entries 1  memlock 4096B

          owner_prog_type xdp  owner jited



|

| **# bpftool map pin id 294 /sys/fs/bpf/bar**

| **# bpftool map dump pinned /sys/fs/bpf/bar**



::



  Found 0 elements



|

| **# bpftool map update pinned /sys/fs/bpf/bar key 0 0 0 0 value pinned /sys/fs/bpf/foo/debug**

| **# bpftool map dump pinned /sys/fs/bpf/bar**



::



  key: 00 00 00 00  value: 22 02 00 00

  Found 1 element



SEE ALSO

========

	**bpf**\ (2),