tools/bpftool: Add bpf_iter support for bptool

Currently, only one command is supported
  bpftool iter pin <bpf_prog.o> <path>

It will pin the trace/iter bpf program in
the object file <bpf_prog.o> to the <path>
where <path> should be on a bpffs mount.

For example,
  $ bpftool iter pin ./bpf_iter_ipv6_route.o \
    /sys/fs/bpf/my_route
User can then do a `cat` to print out the results:
  $ cat /sys/fs/bpf/my_route
    fe800000000000000000000000000000 40 00000000000000000000000000000000 ...
    00000000000000000000000000000000 00 00000000000000000000000000000000 ...
    00000000000000000000000000000001 80 00000000000000000000000000000000 ...
    fe800000000000008c0162fffebdfd57 80 00000000000000000000000000000000 ...
    ff000000000000000000000000000000 08 00000000000000000000000000000000 ...
    00000000000000000000000000000000 00 00000000000000000000000000000000 ...

The implementation for ipv6_route iterator is in one of subsequent
patches.

This patch also added BPF_LINK_TYPE_ITER to link query.

In the future, we may add additional parameters to pin command
by parameterizing the bpf iterator. For example, a map_id or pid
may be added to let bpf program only traverses a single map or task,
similar to kernel seq_file single_open().

We may also add introspection command for targets/iterators by
leveraging the bpf_iter itself.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20200509175920.2477247-1-yhs@fb.com

1 files changed, 83 insertions, 0 deletions

diff --git a/tools/bpf/bpftool/Documentation/bpftool-iter.rst b/tools/bpf/bpftool/Documentation/bpftool-iter.rst
new file mode 100644
index 000000000000..13b173d93890
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+++ b/tools/bpf/bpftool/Documentation/bpftool-iter.rst
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+============
+bpftool-iter
+============
+-------------------------------------------------------------------------------
+tool to create BPF iterators
+-------------------------------------------------------------------------------
+
+:Manual section: 8
+
+SYNOPSIS
+========
+
+	**bpftool** [*OPTIONS*] **iter** *COMMAND*
+
+	*COMMANDS* := { **pin** | **help** }
+
+ITER COMMANDS
+===================
+
+|	**bpftool** **iter pin** *OBJ* *PATH*
+|	**bpftool** **iter help**
+|
+|	*OBJ* := /a/file/of/bpf_iter_target.o
+
+
+DESCRIPTION
+===========
+	**bpftool iter pin** *OBJ* *PATH*
+		  A bpf iterator combines a kernel iterating of
+		  particular kernel data (e.g., tasks, bpf_maps, etc.)
+		  and a bpf program called for each kernel data object
+		  (e.g., one task, one bpf_map, etc.). User space can
+		  *read* kernel iterator output through *read()* syscall.
+
+		  The *pin* command creates a bpf iterator from *OBJ*,
+		  and pin it to *PATH*. The *PATH* should be located
+		  in *bpffs* mount. It must not contain a dot
+		  character ('.'), which is reserved for future extensions
+		  of *bpffs*.
+
+		  User can then *cat PATH* to see the bpf iterator output.
+
+	**bpftool iter 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**).
+
+	-d, --debug
+		  Print all logs available, even debug-level information. This
+		  includes logs from libbpf as well as from the verifier, when
+		  attempting to load programs.
+
+EXAMPLES
+========
+**# bpftool iter pin bpf_iter_netlink.o /sys/fs/bpf/my_netlink**
+
+::
+
+   Create a file-based bpf iterator from bpf_iter_netlink.o and pin it
+   to /sys/fs/bpf/my_netlink
+
+
+SEE ALSO
+========
+	**bpf**\ (2),
+	**bpf-helpers**\ (7),
+	**bpftool**\ (8),
+	**bpftool-prog**\ (8),
+	**bpftool-map**\ (8),
+	**bpftool-link**\ (8),
+	**bpftool-cgroup**\ (8),
+	**bpftool-feature**\ (8),
+	**bpftool-net**\ (8),
+	**bpftool-perf**\ (8),
+	**bpftool-btf**\ (8)
+	**bpftool-gen**\ (8)
+	**bpftool-struct_ops**\ (8)