[PATCH bpf-next v2 0/4] API to access btf_dump emit queue and print single type

[Eduard Zingerman <eddyz87@gmail.com>]

This is a follow-up to the following discussion:
https://lore.kernel.org/bpf/20240503111836.25275-1-jose.marchesi@oracle.com/

As suggested by Andrii, this series adds several API functions to
allow more flexibility with btf dump:
- a function to add a type and all its dependencies to the emit queue;
- functions to provide access to the emit queue owned by btf_dump object;
- a function to print a given type (skipping any dependencies).

This should allow filtering printed types and also adding
attributes / pre-processor statements to specific types.

There are several ways to add such API:
1. The simplest in terms of code changes is to refactor
   btf_dump_emit_type() to push types and forward declarations
   to the emit queue, instead of printing those directly;
2. More intrusive: refactor btf_dump_emit_type() and
   btf_dump_order_type() to avoid doing topological sorting twice and
   put forward declarations to the emit queue at once.

This series opts for (2) as it seems to simplify library code a bit.
For the sake of discussion, source code for option (1) as available at:
https://github.com/eddyz87/bpf/tree/libbpf-sort-for-dump-api-simple

Also, this series opts for the following new API function:

  int btf_dump__dump_one_type(struct btf_dump *d, __u32 id, bool fwd);

As adding _opts variant of btf_dump__dump_type seems a bit clumsy:

  struct btf_dump_opts {
	size_t sz;
	bool fwd;
	bool skip_dependencies;
	bool skip_last_semi;
  };

  int btf_dump__dump_type_opts(struct btf_dump *d, __u32 id,
			       struct btf_dump_opts *opts);

but maybe community would prefer the later variant.

Changes v1->v2:
- fix for build issues reported by CI: do not mark typedefs as ORDERED

v1: https://lore.kernel.org/bpf/20240516230443.3436233-1-eddyz87@gmail.com/

Eduard Zingerman (4):
  libbpf: put forward declarations to btf_dump->emit_queue
  libbpf: API to access btf_dump emit queue and print single type
  selftests/bpf: tests for btf_dump emit queue API
  selftests/bpf: corner case for typedefs handling in btf_dump

 tools/lib/bpf/btf.h                           |  33 ++
 tools/lib/bpf/btf_dump.c                      | 386 +++++++++---------
 tools/lib/bpf/libbpf.map                      |   4 +
 .../selftests/bpf/prog_tests/btf_dump.c       |  86 ++++
 .../bpf/progs/btf_dump_test_case_ordering.c   |  10 +
 5 files changed, 315 insertions(+), 204 deletions(-)

-- 
2.34.1