BPFTOOL-MAP(8) System Manager's Manual BPFTOOL-MAP(8)

bpftool-map - tool for inspection and simple manipulation of eBPF maps

bpftool [OPTIONS] map COMMAND

OPTIONS := { { -j | --json } [{ -p | --pretty }] | { -d | --debug } | { -f | --bpffs } | { -n | --nomount } }

COMMANDS := { show | list | create | dump | update | lookup | getnext | delete | pin | help }

bpftool map { show | list }   [MAP]
bpftool map create     FILE type TYPE key KEY_SIZE value VALUE_SIZE 
entries MAX_ENTRIES name NAME [flags FLAGS] [inner_map MAP] 
[offload_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 freeze     MAP
bpftool map help
MAP := { id MAP_ID | pinned FILE | name MAP_NAME }
DATA := { [hex] BYTES }
PROG := { id PROG_ID | pinned FILE | tag PROG_TAG | name PROG_NAME }
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 | devmap_hash | sockmap | cpumap | xskmap | sockhash
| cgroup_storage | reuseport_sockarray | percpu_cgroup_storage
| queue | stack | sk_storage | struct_ops | ringbuf | inode_storage
| task_storage | bloom_filter | user_ringbuf | cgrp_storage | arena }

Show information about loaded maps. If MAP is specified show information only about given maps, otherwise list all maps currently loaded on the system. In case of name, MAP may match several maps which will all be shown.

Output will start with map ID followed by map type and zero or more named attributes (depending on kernel version).

Since Linux 5.8 bpftool is able to discover information about processes that hold open file descriptors (FDs) against BPF maps. On such kernels bpftool will automatically emit this information as well.

Create a new map with given parameters and pin it to bpffs as FILE.

FLAGS should be an integer which is the combination of desired flags, e.g. 1024 for BPF_F_MMAPABLE (see bpf.h UAPI header for existing flags).

To create maps of type array-of-maps or hash-of-maps, the inner_map keyword must be used to pass an inner map. The kernel needs it to collect metadata related to the inner maps that the new map will work with.

Keyword offload_dev expects a network interface name, and is used to request hardware offload for the map.

Dump all entries in a given MAP. In case of name, MAP may match several maps which will all be dumped.
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 hexadecimal 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.

Lookup key in the map.
Get next key. If key is not specified, get first key.
Remove entry from the map.
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.

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.

Peek next value in the queue or stack.
Push VALUE onto the stack.
Pop and print value from the stack.
Enqueue VALUE into the queue.
Dequeue and print value from the queue.
Freeze the map as read-only from user space. Entries from a frozen map can not longer be updated or deleted with the bpf() system call. This operation is not reversible, and the map remains immutable from user space until its destruction. However, read and write permissions for BPF programs to the map remain unchanged.
Print short help message.

Print short help message (similar to bpftool help).
Print bpftool's version number (similar to bpftool version), the number of the libbpf version in use, and optional features that were included when bpftool was compiled. Optional features include linking against LLVM or libbfd to provide the disassembler for JIT-ted programs (bpftool prog dump jited) and usage of BPF skeletons (some features like bpftool prog profile or showing pids associated to BPF objects may rely on it).
Generate JSON output. For commands that cannot produce JSON, this option has no effect.
Generate human-readable JSON output. Implies -j.
Print all logs available, even debug-level information. This includes logs from libbpf as well as from the verifier, when attempting to load programs.
Show file names of pinned maps.
Do not automatically attempt to mount any virtual file system (such as tracefs or BPF virtual file system) when necessary.

# bpftool map show

10: hash  name some_map  flags 0x0
      key 4B  value 8B  max_entries 2048  memlock 167936B
      pids systemd(1)

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

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