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

On Tue, Feb 1, 2022 at 3:57 PM Quentin Monnet [off-list ref] wrote:

2022-01-28 17:33 UTC-0500 ~ Mauricio Vásquez [off-list ref]

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>

Hi, note that the patchset (or at least, this patch) does not apply
cleanly. Can you please double-check that it is based on bpf-next?

I missed one commit on this submission...

quoted

---
 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);
+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);
+void bpf_core_free_cands(struct bpf_core_cand_list *cands);

I wonder if these might deserve a comment to mention that they are
exposed for bpftool? I fear someone might attempt to clean it up and
remove the unused exports otherwise.

I added a comment there.