tools: bpftool: Add "inner_map" to "bpftool map create" outer maps

There is no support for creating maps of types array-of-map or
hash-of-map in bpftool. This is because the kernel needs an inner_map_fd
to collect metadata on the inner maps to be supported by the new map,
but bpftool does not provide a way to pass this file descriptor.

Add a new optional "inner_map" keyword that can be used to pass a
reference to a map, retrieve a fd to that map, and pass it as the
inner_map_fd.

Add related documentation and bash completion. Note that we can
reference the inner map by its name, meaning we can have several times
the keyword "name" with different meanings (mandatory outer map name,
and possibly a name to use to find the inner_map_fd). The bash
completion will offer it just once, and will not suggest "name" on the
following command:

    # bpftool map create /sys/fs/bpf/my_outer_map type hash_of_maps \
        inner_map name my_inner_map [TAB]

Fixing that specific case seems too convoluted. Completion will work as
expected, however, if the outer map name comes first and the "inner_map
name ..." is passed second.

Signed-off-by: Quentin Monnet <quentin@isovalent.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/20200910102652.10509-4-quentin@isovalent.com

1 files changed, 8 insertions, 2 deletions

diff --git a/tools/bpf/bpftool/Documentation/bpftool-map.rst b/tools/bpf/bpftool/Documentation/bpftool-map.rst
index 4b42629ade3e..8eac254ade48 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-map.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-map.rst
@@ -23,7 +23,8 @@ 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*]
+|		**entries** *MAX_ENTRIES* **name** *NAME* [**flags** *FLAGS*] [**inner_map** *MAP*] \
+|		[**dev** *NAME*]
 |	**bpftool** **map dump**       *MAP*
 |	**bpftool** **map update**     *MAP* [**key** *DATA*] [**value** *VALUE*] [*UPDATE_FLAGS*]
 |	**bpftool** **map lookup**     *MAP* [**key** *DATA*]
@@ -67,7 +68,7 @@ DESCRIPTION
 		  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*] [**dev** *NAME*]
+	**bpftool map create** *FILE* **type** *TYPE* **key** *KEY_SIZE* **value** *VALUE_SIZE*  **entries** *MAX_ENTRIES* **name** *NAME* [**flags** *FLAGS*] [**inner_map** *MAP*] [**dev** *NAME*]
 		  Create a new map with given parameters and pin it to *bpffs*
 		  as *FILE*.
 
@@ -75,6 +76,11 @@ DESCRIPTION
 		  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 **dev** expects a network interface name, and is used
 		  to request hardware offload for the map.