libbpf: Streamline error reporting for high-level APIs

Implement changes to error reporting for high-level libbpf APIs to make them
less surprising and less error-prone to users:
  - in all the cases when error happens, errno is set to an appropriate error
    value;
  - in libbpf 1.0 mode, all pointer-returning APIs return NULL on error and
    error code is communicated through errno; this applies both to APIs that
    already returned NULL before (so now they communicate more detailed error
    codes), as well as for many APIs that used ERR_PTR() macro and encoded
    error numbers as fake pointers.
  - in legacy (default) mode, those APIs that were returning ERR_PTR(err),
    continue doing so, but still set errno.

With these changes, errno can be always used to extract actual error,
regardless of legacy or libbpf 1.0 modes. This is utilized internally in
libbpf in places where libbpf uses it's own high-level APIs.
libbpf_get_error() is adapted to handle both cases completely transparently to
end-users (and is used by libbpf consistently as well).

More context, justification, and discussion can be found in "Libbpf: the road
to v1.0" document ([0]).

  [0] https://docs.google.com/document/d/1UyjTZuPFWiPFyKk1tV5an11_iaRuec6U-ZESZ54nNTY

Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Acked-by: Toke Høiland-Jørgensen <toke@redhat.com>
Link: https://lore.kernel.org/bpf/20210525035935.1461796-5-andrii@kernel.org

1 files changed, 7 insertions, 7 deletions

diff --git a/tools/lib/bpf/btf_dump.c b/tools/lib/bpf/btf_dump.c
index 5e2809d685bf..5dc6b5172bb3 100644
--- a/tools/lib/bpf/btf_dump.c
+++ b/tools/lib/bpf/btf_dump.c
@@ -128,7 +128,7 @@ struct btf_dump *btf_dump__new(const struct btf *btf,
 
 	d = calloc(1, sizeof(struct btf_dump));
 	if (!d)
-		return ERR_PTR(-ENOMEM);
+		return libbpf_err_ptr(-ENOMEM);
 
 	d->btf = btf;
 	d->btf_ext = btf_ext;
@@ -156,7 +156,7 @@ struct btf_dump *btf_dump__new(const struct btf *btf,
 	return d;
 err:
 	btf_dump__free(d);
-	return ERR_PTR(err);
+	return libbpf_err_ptr(err);
 }
 
 static int btf_dump_resize(struct btf_dump *d)
@@ -236,16 +236,16 @@ int btf_dump__dump_type(struct btf_dump *d, __u32 id)
 	int err, i;
 
 	if (id > btf__get_nr_types(d->btf))
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 
 	err = btf_dump_resize(d);
 	if (err)
-		return err;
+		return libbpf_err(err);
 
 	d->emit_queue_cnt = 0;
 	err = btf_dump_order_type(d, id, false);
 	if (err < 0)
-		return err;
+		return libbpf_err(err);
 
 	for (i = 0; i < d->emit_queue_cnt; i++)
 		btf_dump_emit_type(d, d->emit_queue[i], 0 /*top-level*/);
@@ -1075,11 +1075,11 @@ int btf_dump__emit_type_decl(struct btf_dump *d, __u32 id,
 	int lvl, err;
 
 	if (!OPTS_VALID(opts, btf_dump_emit_type_decl_opts))
-		return -EINVAL;
+		return libbpf_err(-EINVAL);
 
 	err = btf_dump_resize(d);
 	if (err)
-		return -EINVAL;
+		return libbpf_err(err);
 
 	fname = OPTS_GET(opts, field_name, "");
 	lvl = OPTS_GET(opts, indent_level, 0);