[PATCH v2 bpf-next 0/4] libbpf: BTF dumper support for typed data

[Alan Maguire <alan.maguire@oracle.com>]

Add a libbpf dumper function that supports dumping a representation
of data passed in using the BTF id associated with the data in a
manner similar to the bpf_snprintf_btf helper.

Default output format is identical to that dumped by bpf_snprintf_btf(),
for example a "struct sk_buff" representation would look like this:

struct sk_buff){
 (union){
  (struct){
   .next = (struct sk_buff *)0xffffffffffffffff,
   .prev = (struct sk_buff *)0xffffffffffffffff,
   (union){
    .dev = (struct net_device *)0xffffffffffffffff,
    .dev_scratch = (long unsigned int)18446744073709551615,
   },
  },
...

Patches 1 and 2 make functions available that are needed during
dump operations.

Patch 3 implements the dump functionality in a manner similar
to that in kernel/bpf/btf.c, but with a view to fitting into
libbpf more naturally.  For example, rather than using flags,
boolean dump options are used to control output.

Patch 4 is a selftest that utilizes a dump printf function
to snprintf the dump output to a string for comparison with
expected output.  Tests deliberately mirror those in
snprintf_btf helper test to keep output consistent.

Changes since RFC [1]

- The initial approach explored was to share the kernel code
  with libbpf using #defines to paper over the different needs;
  however it makes more sense to try and fit in with libbpf
  code style for maintenance.  A comment in the code points at
  the implementation in kernel/bpf/btf.c and notes that any
  issues found in it should be fixed there or vice versa;
  mirroring the tests should help with this also
  (Andrii)

[1] https://lore.kernel.org/bpf/1610386373-24162-1-git-send-email-alan.maguire@oracle.com/T/#t

Alan Maguire (4):
  libbpf: add btf_has_size() and btf_int() inlines
  libbpf: make skip_mods_and_typedefs available internally in libbpf
  libbpf: BTF dumper support for typed data
  selftests/bpf: add dump type data tests to btf dump tests

 tools/lib/bpf/btf.h                               |  36 +
 tools/lib/bpf/btf_dump.c                          | 974 ++++++++++++++++++++++
 tools/lib/bpf/libbpf.c                            |   4 +-
 tools/lib/bpf/libbpf.map                          |   5 +
 tools/lib/bpf/libbpf_internal.h                   |   2 +
 tools/testing/selftests/bpf/prog_tests/btf_dump.c | 233 ++++++
 6 files changed, 1251 insertions(+), 3 deletions(-)

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1.8.3.1