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authorKui-Feng Lee <thinker.li@gmail.com>2024-02-29 07:45:22 +0100
committerAndrii Nakryiko <andrii@kernel.org>2024-02-29 23:23:53 +0100
commitf2e81192e07e87897ff1296c96775eceea8f582a (patch)
tree39d67b886bcd562accc2b99f99d9c9c5f85e5855 /tools/bpf
parentbpftool: Generated shadow variables for struct_ops maps. (diff)
downloadlinux-f2e81192e07e87897ff1296c96775eceea8f582a.tar.xz
linux-f2e81192e07e87897ff1296c96775eceea8f582a.zip
bpftool: Add an example for struct_ops map and shadow type.
The example in bpftool-gen.8 explains how to use the pointer of the shadow type to change the value of a field of a struct_ops map. Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com> Signed-off-by: Andrii Nakryiko <andrii@kernel.org> Reviewed-by: Quentin Monnet <quentin@isovalent.com> Link: https://lore.kernel.org/bpf/20240229064523.2091270-5-thinker.li@gmail.com
Diffstat (limited to 'tools/bpf')
-rw-r--r--tools/bpf/bpftool/Documentation/bpftool-gen.rst58
1 files changed, 52 insertions, 6 deletions
diff --git a/tools/bpf/bpftool/Documentation/bpftool-gen.rst b/tools/bpf/bpftool/Documentation/bpftool-gen.rst
index 5006e724d1bc..5e60825818dd 100644
--- a/tools/bpf/bpftool/Documentation/bpftool-gen.rst
+++ b/tools/bpf/bpftool/Documentation/bpftool-gen.rst
@@ -257,18 +257,48 @@ EXAMPLES
return 0;
}
-This is example BPF application with two BPF programs and a mix of BPF maps
-and global variables. Source code is split across two source code files.
+**$ cat example3.bpf.c**
+
+::
+
+ #include <linux/ptrace.h>
+ #include <linux/bpf.h>
+ #include <bpf/bpf_helpers.h>
+ /* This header file is provided by the bpf_testmod module. */
+ #include "bpf_testmod.h"
+
+ int test_2_result = 0;
+
+ /* bpf_Testmod.ko calls this function, passing a "4"
+ * and testmod_map->data.
+ */
+ SEC("struct_ops/test_2")
+ void BPF_PROG(test_2, int a, int b)
+ {
+ test_2_result = a + b;
+ }
+
+ SEC(".struct_ops")
+ struct bpf_testmod_ops testmod_map = {
+ .test_2 = (void *)test_2,
+ .data = 0x1,
+ };
+
+This is example BPF application with three BPF programs and a mix of BPF
+maps and global variables. Source code is split across three source code
+files.
**$ clang --target=bpf -g example1.bpf.c -o example1.bpf.o**
**$ clang --target=bpf -g example2.bpf.c -o example2.bpf.o**
-**$ bpftool gen object example.bpf.o example1.bpf.o example2.bpf.o**
+**$ clang --target=bpf -g example3.bpf.c -o example3.bpf.o**
+
+**$ bpftool gen object example.bpf.o example1.bpf.o example2.bpf.o example3.bpf.o**
-This set of commands compiles *example1.bpf.c* and *example2.bpf.c*
-individually and then statically links respective object files into the final
-BPF ELF object file *example.bpf.o*.
+This set of commands compiles *example1.bpf.c*, *example2.bpf.c* and
+*example3.bpf.c* individually and then statically links respective object
+files into the final BPF ELF object file *example.bpf.o*.
**$ bpftool gen skeleton example.bpf.o name example | tee example.skel.h**
@@ -291,7 +321,15 @@ BPF ELF object file *example.bpf.o*.
struct bpf_map *data;
struct bpf_map *bss;
struct bpf_map *my_map;
+ struct bpf_map *testmod_map;
} maps;
+ struct {
+ struct example__testmod_map__bpf_testmod_ops {
+ const struct bpf_program *test_1;
+ const struct bpf_program *test_2;
+ int data;
+ } *testmod_map;
+ } struct_ops;
struct {
struct bpf_program *handle_sys_enter;
struct bpf_program *handle_sys_exit;
@@ -304,6 +342,7 @@ BPF ELF object file *example.bpf.o*.
struct {
int x;
} data;
+ int test_2_result;
} *bss;
struct example__data {
_Bool global_flag;
@@ -342,10 +381,16 @@ BPF ELF object file *example.bpf.o*.
skel->rodata->param1 = 128;
+ /* Change the value through the pointer of shadow type */
+ skel->struct_ops.testmod_map->data = 13;
+
err = example__load(skel);
if (err)
goto cleanup;
+ /* The result of the function test_2() */
+ printf("test_2_result: %d\n", skel->bss->test_2_result);
+
err = example__attach(skel);
if (err)
goto cleanup;
@@ -372,6 +417,7 @@ BPF ELF object file *example.bpf.o*.
::
+ test_2_result: 17
my_map name: my_map
sys_enter prog FD: 8
my_static_var: 7