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linux/tools/bpf/bpftool/Documentation/bpftool-map.rst
Quentin Monnet 49eb7ab3b2 tools: bpftool: add basic probe capability, probe syscall availability 
Add a new component and command for bpftool, in order to probe the
system to dump a set of eBPF-related parameters so that users can know
what features are available on the system.

Parameters are dumped in plain or JSON output (with -j/-p options).

The current patch introduces probing of one simple parameter:
availability of the bpf() system call. Later commits
will add other probes.

Sample output:

    # bpftool feature probe kernel
    Scanning system call availability...
    bpf() syscall is available

    # bpftool --json --pretty feature probe kernel
    {
        "syscall_config": {
            "have_bpf_syscall": true
        }
    }

The optional "kernel" keyword enforces probing of the current system,
which is the only possible behaviour at this stage. It can be safely
omitted.

The feature comes with the relevant man page, but bash completion will
come in a dedicated commit.

v3:
- Do not probe kernel version. Contrarily to what is written below for
  v2, we can have the kernel version retrieved in libbpf instead of
  bpftool (in the patch adding probing for program types).

v2:
- Remove C-style macros output from this patch.
- Even though kernel version is no longer needed for testing kprobes
  availability, note that we still collect it in this patch so that
  bpftool gets able to probe (in next patches) older kernels as well.

Signed-off-by: Quentin Monnet <quentin.monnet@netronome.com>
Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Stanislav Fomichev <sdf@google.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
2019-01-22 22:15:40 -08:00

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================
bpftool-map
================
-------------------------------------------------------------------------------
tool for inspection and simple manipulation of eBPF maps
-------------------------------------------------------------------------------
:Manual section: 8
SYNOPSIS
========
**bpftool** [*OPTIONS*] **map** *COMMAND*
*OPTIONS* := { { **-j** | **--json** } [{ **-p** | **--pretty** }] | { **-f** | **--bpffs** } }
*COMMANDS* :=
{ **show** | **list** | **create** | **dump** | **update** | **lookup** | **getnext**
| **delete** | **pin** | **help** }
MAP COMMANDS
=============
| **bpftool** **map { show | list }** [*MAP*]
| **bpftool** **map create** *FILE* **type** *TYPE* **key** *KEY_SIZE* **value** *VALUE_SIZE* \
| **entries** *MAX_ENTRIES* **name** *NAME* [**flags** *FLAGS*] [**dev** *NAME*]
| **bpftool** **map dump** *MAP*
| **bpftool** **map update** *MAP* [**key** *DATA*] [**value** *VALUE*] [*UPDATE_FLAGS*]
| **bpftool** **map lookup** *MAP* [**key** *DATA*]
| **bpftool** **map getnext** *MAP* [**key** *DATA*]
| **bpftool** **map delete** *MAP* **key** *DATA*
| **bpftool** **map pin** *MAP* *FILE*
| **bpftool** **map event_pipe** *MAP* [**cpu** *N* **index** *M*]
| **bpftool** **map peek** *MAP*
| **bpftool** **map push** *MAP* **value** *VALUE*
| **bpftool** **map pop** *MAP*
| **bpftool** **map enqueue** *MAP* **value** *VALUE*
| **bpftool** **map dequeue** *MAP*
| **bpftool** **map help**
|
| *MAP* := { **id** *MAP_ID* | **pinned** *FILE* }
| *DATA* := { [**hex**] *BYTES* }
| *PROG* := { **id** *PROG_ID* | **pinned** *FILE* | **tag** *PROG_TAG* }
| *VALUE* := { *DATA* | *MAP* | *PROG* }
| *UPDATE_FLAGS* := { **any** | **exist** | **noexist** }
| *TYPE* := { **hash** | **array** | **prog_array** | **perf_event_array** | **percpu_hash**
| | **percpu_array** | **stack_trace** | **cgroup_array** | **lru_hash**
| | **lru_percpu_hash** | **lpm_trie** | **array_of_maps** | **hash_of_maps**
| | **devmap** | **sockmap** | **cpumap** | **xskmap** | **sockhash**
| | **cgroup_storage** | **reuseport_sockarray** | **percpu_cgroup_storage**
| | **queue** | **stack** }
DESCRIPTION
===========
**bpftool map { show | list }** [*MAP*]
Show information about loaded maps. If *MAP* is specified
show information only about given map, otherwise list all
maps currently loaded on the system.
Output will start with map ID followed by map type and
zero or more named attributes (depending on kernel version).
**bpftool map create** *FILE* **type** *TYPE* **key** *KEY_SIZE* **value** *VALUE_SIZE* **entries** *MAX_ENTRIES* **name** *NAME* [**flags** *FLAGS*] [**dev** *NAME*]
Create a new map with given parameters and pin it to *bpffs*
as *FILE*.
**bpftool map dump** *MAP*
Dump all entries in a given *MAP*.
**bpftool map update** *MAP* [**key** *DATA*] [**value** *VALUE*] [*UPDATE_FLAGS*]
Update map entry for a given *KEY*.
*UPDATE_FLAGS* can be one of: **any** update existing entry
or add if doesn't exit; **exist** update only if entry already
exists; **noexist** update only if entry doesn't exist.
If the **hex** keyword is provided in front of the bytes
sequence, the bytes are parsed as hexadeximal values, even if
no "0x" prefix is added. If the keyword is not provided, then
the bytes are parsed as decimal values, unless a "0x" prefix
(for hexadecimal) or a "0" prefix (for octal) is provided.
**bpftool map lookup** *MAP* [**key** *DATA*]
Lookup **key** in the map.
**bpftool map getnext** *MAP* [**key** *DATA*]
Get next key. If *key* is not specified, get first key.
**bpftool map delete** *MAP* **key** *DATA*
Remove entry from the map.
**bpftool map pin** *MAP* *FILE*
Pin map *MAP* as *FILE*.
Note: *FILE* must be located in *bpffs* mount. It must not
contain a dot character ('.'), which is reserved for future
extensions of *bpffs*.
**bpftool** **map event_pipe** *MAP* [**cpu** *N* **index** *M*]
Read events from a BPF_MAP_TYPE_PERF_EVENT_ARRAY map.
Install perf rings into a perf event array map and dump
output of any bpf_perf_event_output() call in the kernel.
By default read the number of CPUs on the system and
install perf ring for each CPU in the corresponding index
in the array.
If **cpu** and **index** are specified, install perf ring
for given **cpu** at **index** in the array (single ring).
Note that installing a perf ring into an array will silently
replace any existing ring. Any other application will stop
receiving events if it installed its rings earlier.
**bpftool map peek** *MAP*
Peek next **value** in the queue or stack.
**bpftool map push** *MAP* **value** *VALUE*
Push **value** onto the stack.
**bpftool map pop** *MAP*
Pop and print **value** from the stack.
**bpftool map enqueue** *MAP* **value** *VALUE*
Enqueue **value** into the queue.
**bpftool map dequeue** *MAP*
Dequeue and print **value** from the queue.
**bpftool map help**
Print short help message.
OPTIONS
=======
-h, --help
Print short generic help message (similar to **bpftool help**).
-v, --version
Print version number (similar to **bpftool version**).
-j, --json
Generate JSON output. For commands that cannot produce JSON, this
option has no effect.
-p, --pretty
Generate human-readable JSON output. Implies **-j**.
-f, --bpffs
Show file names of pinned maps.
-n, --nomount
Do not automatically attempt to mount any virtual file system
(such as tracefs or BPF virtual file system) when necessary.
EXAMPLES
========
**# bpftool map show**
::
10: hash name some_map flags 0x0
key 4B value 8B max_entries 2048 memlock 167936B
The following three commands are equivalent:
|
| **# bpftool map update id 10 key hex 20 c4 b7 00 value hex 0f ff ff ab 01 02 03 4c**
| **# bpftool map update id 10 key 0x20 0xc4 0xb7 0x00 value 0x0f 0xff 0xff 0xab 0x01 0x02 0x03 0x4c**
| **# bpftool map update id 10 key 32 196 183 0 value 15 255 255 171 1 2 3 76**
**# bpftool map lookup id 10 key 0 1 2 3**
::
key: 00 01 02 03 value: 00 01 02 03 04 05 06 07
**# bpftool map dump id 10**
::
key: 00 01 02 03 value: 00 01 02 03 04 05 06 07
key: 0d 00 07 00 value: 02 00 00 00 01 02 03 04
Found 2 elements
**# bpftool map getnext id 10 key 0 1 2 3**
::
key:
00 01 02 03
next key:
0d 00 07 00
|
| **# mount -t bpf none /sys/fs/bpf/**
| **# 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),
**bpf-helpers**\ (7),
**bpftool**\ (8),
**bpftool-prog**\ (8),
**bpftool-cgroup**\ (8),
**bpftool-feature**\ (8),
**bpftool-net**\ (8),
**bpftool-perf**\ (8)
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