Re: [PATCH bpf-next v5 1/9] libbpf: Implement changes needed for BTFGen in bpftool

On Wed, Feb 2, 2022 at 1:54 PM Andrii Nakryiko
[off-list ref] wrote:

On Fri, Jan 28, 2022 at 2:33 PM Mauricio Vásquez [off-list ref] wrote:

quoted

This commit extends libbpf with the features that are needed to
implement BTFGen:

- Implement bpf_core_create_cand_cache() and bpf_core_free_cand_cache()
to handle candidates cache.
- Expose bpf_core_add_cands() and bpf_core_free_cands to handle
candidates list.
- Expose bpf_core_calc_relo_insn() to bpftool.

Signed-off-by: Mauricio Vásquez <redacted>
Signed-off-by: Rafael David Tinoco <redacted>
Signed-off-by: Lorenzo Fontana <redacted>
Signed-off-by: Leonardo Di Donato <redacted>
---
 tools/lib/bpf/libbpf.c          | 44 ++++++++++++++++++++++-----------
 tools/lib/bpf/libbpf_internal.h | 12 +++++++++
 2 files changed, 41 insertions(+), 15 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 12771f71a6e7..61384d219e28 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c

@@ -5195,18 +5195,18 @@ size_t bpf_core_essential_name_len(const char *name)
        return n;
 }

-static void bpf_core_free_cands(struct bpf_core_cand_list *cands)
+void bpf_core_free_cands(struct bpf_core_cand_list *cands)
 {
        free(cands->cands);
        free(cands);
 }

-static int bpf_core_add_cands(struct bpf_core_cand *local_cand,
-                             size_t local_essent_len,
-                             const struct btf *targ_btf,
-                             const char *targ_btf_name,
-                             int targ_start_id,
-                             struct bpf_core_cand_list *cands)
+int bpf_core_add_cands(struct bpf_core_cand *local_cand,
+                      size_t local_essent_len,
+                      const struct btf *targ_btf,
+                      const char *targ_btf_name,
+                      int targ_start_id,
+                      struct bpf_core_cand_list *cands)
 {
        struct bpf_core_cand *new_cands, *cand;
        const struct btf_type *t, *local_t;

@@ -5577,6 +5577,25 @@ static int bpf_core_resolve_relo(struct bpf_program *prog,
                                       targ_res);
 }

+struct hashmap *bpf_core_create_cand_cache(void)
+{
+       return hashmap__new(bpf_core_hash_fn, bpf_core_equal_fn, NULL);
+}
+
+void bpf_core_free_cand_cache(struct hashmap *cand_cache)
+{
+       struct hashmap_entry *entry;
+       int i;
+
+       if (IS_ERR_OR_NULL(cand_cache))
+               return;
+
+       hashmap__for_each_entry(cand_cache, entry, i) {
+               bpf_core_free_cands(entry->value);
+       }
+       hashmap__free(cand_cache);
+}
+
 static int
 bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
 {

@@ -5584,7 +5603,6 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
        struct bpf_core_relo_res targ_res;
        const struct bpf_core_relo *rec;
        const struct btf_ext_info *seg;
-       struct hashmap_entry *entry;
        struct hashmap *cand_cache = NULL;
        struct bpf_program *prog;
        struct bpf_insn *insn;

@@ -5603,7 +5621,7 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
                }
        }

-       cand_cache = hashmap__new(bpf_core_hash_fn, bpf_core_equal_fn, NULL);
+       cand_cache = bpf_core_create_cand_cache();
        if (IS_ERR(cand_cache)) {
                err = PTR_ERR(cand_cache);
                goto out;

@@ -5694,12 +5712,8 @@ bpf_object__relocate_core(struct bpf_object *obj, const char *targ_btf_path)
        btf__free(obj->btf_vmlinux_override);
        obj->btf_vmlinux_override = NULL;

-       if (!IS_ERR_OR_NULL(cand_cache)) {
-               hashmap__for_each_entry(cand_cache, entry, i) {
-                       bpf_core_free_cands(entry->value);
-               }
-               hashmap__free(cand_cache);
-       }
+       bpf_core_free_cand_cache(cand_cache);
+
        return err;
 }

diff --git a/tools/lib/bpf/libbpf_internal.h b/tools/lib/bpf/libbpf_internal.h
index bc86b82e90d1..686a5654262b 100644
--- a/tools/lib/bpf/libbpf_internal.h
+++ b/tools/lib/bpf/libbpf_internal.h

@@ -529,4 +529,16 @@ static inline int ensure_good_fd(int fd)
        return fd;
 }

+struct hashmap;
+
+struct hashmap *bpf_core_create_cand_cache(void);
+void bpf_core_free_cand_cache(struct hashmap *cand_cache);

looking at patch #5, there is nothing special about this cand_cache,
it's just a hashmap from u32 to some pointer. There is no need for
libbpf to expose it to bpftool, you already have hashmap itself and
also btfgen_hash_fn and equality callback, just do the same thing as
you do with btfgen_info->types hashmap.

I'll drop them and handle the hashmap directly from bpftool.