[PATCH bpf-next v5 5/9] bpftool: Generate skeleton for global percpu data

[Leon Hwang]

Enhance bpftool to generate skeletons that properly handle global percpu
variables. The generated skeleton now includes a dedicated structure for
percpu data, allowing users to initialize and access percpu variables more
efficiently.

For global percpu variables, the skeleton now includes a nested
structure, e.g.:

struct test_global_percpu_data {
        struct bpf_object_skeleton *skeleton;
        struct bpf_object *obj;
        struct {
                struct bpf_map *percpu;
        } maps;
        // ...
        struct test_global_percpu_data__percpu {
                int data;
                char run;
                struct {
                        char set;
                        int i;
                        int nums[7];
                } struct_data;
                int nums[7];
        } *percpu;

        // ...
};

  * The "struct test_global_percpu_data__percpu *percpu" points to
    initialized data, which is actually "maps.percpu->mmaped".
  * Before loading the skeleton, updating the
    "struct test_global_percpu_data__percpu *percpu" modifies the initial
    value of the corresponding global percpu variables.
  * After loading the skeleton, "maps.percpu->mmaped" has been marked as
    read-only in libbpf. If users want to update the global percpu
    variables, they have to update the "maps.percpu" map instead.

Signed-off-by: Leon Hwang <leon.hw...@linux.dev>
---
 tools/bpf/bpftool/gen.c | 24 ++++++++++++++----------
 1 file changed, 14 insertions(+), 10 deletions(-)

diff --git a/tools/bpf/bpftool/gen.c b/tools/bpf/bpftool/gen.c
index 6ae7262ebe0c..e0c5c643fe9e 100644
--- a/tools/bpf/bpftool/gen.c
+++ b/tools/bpf/bpftool/gen.c
@@ -92,7 +92,7 @@ static void get_header_guard(char *guard, const char 
*obj_name, const char *suff
 
 static bool get_map_ident(const struct bpf_map *map, char *buf, size_t buf_sz)
 {
-       static const char *sfxs[] = { ".data", ".rodata", ".bss", ".kconfig" };
+       static const char *sfxs[] = { ".data", ".rodata", ".bss", ".percpu", 
".kconfig" };
        const char *name = bpf_map__name(map);
        int i, n;
 
@@ -117,7 +117,7 @@ static bool get_map_ident(const struct bpf_map *map, char 
*buf, size_t buf_sz)
 
 static bool get_datasec_ident(const char *sec_name, char *buf, size_t buf_sz)
 {
-       static const char *pfxs[] = { ".data", ".rodata", ".bss", ".kconfig" };
+       static const char *pfxs[] = { ".data", ".rodata", ".bss", ".percpu", 
".kconfig" };
        int i, n;
 
        /* recognize hard coded LLVM section name */
@@ -254,6 +254,11 @@ static const struct btf_type *find_type_for_map(struct btf 
*btf, const char *map
        return NULL;
 }
 
+static bool bpf_map_is_percpu_data(const struct bpf_map *map)
+{
+       return bpf_map__is_internal(map) && bpf_map__type(map) == 
BPF_MAP_TYPE_PERCPU_ARRAY;
+}
+
 static bool is_mmapable_map(const struct bpf_map *map, char *buf, size_t sz)
 {
        size_t tmp_sz;
@@ -263,13 +268,12 @@ static bool is_mmapable_map(const struct bpf_map *map, 
char *buf, size_t sz)
                return true;
        }
 
-       if (!bpf_map__is_internal(map) || !(bpf_map__map_flags(map) & 
BPF_F_MMAPABLE))
-               return false;
-
-       if (!get_map_ident(map, buf, sz))
-               return false;
+       if (bpf_map__is_internal(map) &&
+           ((bpf_map__map_flags(map) & BPF_F_MMAPABLE) || 
bpf_map_is_percpu_data(map)) &&
+           get_map_ident(map, buf, sz))
+               return true;
 
-       return true;
+       return false;
 }
 
 static int codegen_datasecs(struct bpf_object *obj, const char *obj_name)
@@ -669,7 +673,7 @@ static void codegen_destroy(struct bpf_object *obj, const 
char *obj_name)
                if (!get_map_ident(map, ident, sizeof(ident)))
                        continue;
                if (bpf_map__is_internal(map) &&
-                   (bpf_map__map_flags(map) & BPF_F_MMAPABLE))
+                   ((bpf_map__map_flags(map) & BPF_F_MMAPABLE) || 
bpf_map_is_percpu_data(map)))
                        printf("\tskel_free_map_data(skel->%1$s, 
skel->maps.%1$s.initial_value, %2$zu);\n",
                               ident, bpf_map_mmap_sz(map));
                codegen("\
@@ -847,7 +851,7 @@ static int gen_trace(struct bpf_object *obj, const char 
*obj_name, const char *h
        bpf_object__for_each_map(map, obj) {
                const char *mmap_flags;
 
-               if (!is_mmapable_map(map, ident, sizeof(ident)))
+               if (!is_mmapable_map(map, ident, sizeof(ident)) || 
bpf_map_is_percpu_data(map))
                        continue;
 
                if (bpf_map__map_flags(map) & BPF_F_RDONLY_PROG)
-- 
2.54.0