bpftool: Add feature list (prog/map/link/attach types, helpers)

Add a "bpftool feature list" subcommand to list BPF "features".
Contrarily to "bpftool feature probe", this is not about the features
available on the system. Instead, it lists all features known to bpftool
from compilation time; in other words, all program, map, attach, link
types known to the libbpf version in use, and all helpers found in the
UAPI BPF header.

The first use case for this feature is bash completion: running the
command provides a list of types that can be used to produce the list of
candidate map types, for example.

Now that bpftool uses "standard" names provided by libbpf for the
program, map, link, and attach types, having the ability to list these
types and helpers could also be useful in scripts to loop over existing
items.

Sample output:

    # bpftool feature list prog_types | grep -vw unspec | head -n 6
    socket_filter
    kprobe
    sched_cls
    sched_act
    tracepoint
    xdp

    # bpftool -p feature list map_types | jq '.[1]'
    "hash"

    # bpftool feature list attach_types | grep '^cgroup_'
    cgroup_inet_ingress
    cgroup_inet_egress
    [...]
    cgroup_inet_sock_release

    # bpftool feature list helpers | grep -vw bpf_unspec | wc -l
    207

The "unspec" types and helpers are not filtered out by bpftool, so as to
remain closer to the enums, and to preserve the indices in the JSON
arrays (e.g. "hash" at index 1 == BPF_MAP_TYPE_HASH in map types list).

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Daniel Müller <deso@posteo.net>
Link: https://lore.kernel.org/bpf/20220629203637.138944-2-quentin@isovalent.com

1 files changed, 12 insertions, 0 deletions

diff --git a/tools/bpf/bpftool/Documentation/bpftool-feature.rst b/tools/bpf/bpftool/Documentation/bpftool-feature.rst
index 4ce9a77bc1e0..c08064628d39 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-feature.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-feature.rst
@@ -24,9 +24,11 @@ FEATURE COMMANDS
 ================
 
 |	**bpftool** **feature probe** [*COMPONENT*] [**full**] [**unprivileged**] [**macros** [**prefix** *PREFIX*]]
+|	**bpftool** **feature list** *GROUP*
 |	**bpftool** **feature help**
 |
 |	*COMPONENT* := { **kernel** | **dev** *NAME* }
+|	*GROUP* := { **prog_types** | **map_types** | **attach_types** | **link_types** | **helpers** }
 
 DESCRIPTION
 ===========
@@ -70,6 +72,16 @@ DESCRIPTION
 		  The keywords **full**, **macros** and **prefix** have the
 		  same role as when probing the kernel.
 
+	**bpftool feature list** *GROUP*
+		  List items known to bpftool. These can be BPF program types
+		  (**prog_types**), BPF map types (**map_types**), attach types
+		  (**attach_types**), link types (**link_types**), or BPF helper
+		  functions (**helpers**). The command does not probe the system, but
+		  simply lists the elements that bpftool knows from compilation time,
+		  as provided from libbpf (for all object types) or from the BPF UAPI
+		  header (list of helpers). This can be used in scripts to iterate over
+		  BPF types or helpers.
+
 	**bpftool feature help**
 		  Print short help message.