| Manual section: | 8 |
|---|
bpftool [OPTIONS] map COMMAND
OPTIONS := { |COMMON_OPTIONS| | { -f | --bpffs } | { -n | --nomount } }
COMMANDS := { show | list | create | dump | update | lookup | getnext | delete | pin | help }
- bpftool map { show | list } [MAP]
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.
- 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]
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.
- bpftool map dump MAP
- Dump all entries in a given MAP. In case of name, MAP may match several maps which will all be dumped.
- 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 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.
- 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 freeze MAP
- 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.
- bpftool map help
- Print short help message.
| -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. |
# 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 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
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).
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
Found 0 elements
key: 00 00 00 00 value: 22 02 00 00 Found 1 element