On Thu, Jun 25, 2020 at 4:47 PM Jiri Olsa [off-list ref] wrote:

hi,
adding d_path helper to return full path for 'path' object.

In a preparation for that, this patchset also adds support for BTF ID
whitelists, because d_path can't be called from any probe due to its
locks usage. The whitelists allow verifier to check if the caller is
one of the functions from the whitelist.

The whitelist is implemented in a generic way. This patchset introduces
macros that allow to define lists of BTF IDs, which are compiled in
the kernel image in a new .BTF.ids ELF section.

The generic way of BTF ID lists allows us to use them in other places
in kernel (than just for whitelists), that could use static BTF ID
values compiled in and it's also implemented in this patchset.

I originally added and used 'file_path' helper, which did the same,
but used 'struct file' object. Then realized that file_path is just
a wrapper for d_path, so we'd cover more calling sites if we add
d_path helper and allowed resolving BTF object within another object,
so we could call d_path also with file pointer, like:

  bpf_d_path(&file->f_path, buf, size);

This feature is mainly to be able to add dpath (filepath originally)
function to bpftrace:

  # bpftrace -e 'kfunc:vfs_open { printf("%s\n", dpath(args->path)); }'

v4 changes:
  - added ID sanity checks in btf_resolve_helper_id [Andrii]
  - resolve bpf_ctx_convert via BTF_ID [Andrii]
  - keep bpf_access_type in btf_struct_access [Andrii]
  - rename whitelist to se and use struct btf_id_set [Andrii]
  - several fixes for d_path prog/verifier tests [Andrii]
  - added union and typedefs types support [Andrii]
  - rename btfid to resolve_btfids [Andrii]
  - fix segfault in resolve_btfids [John]
  - rename section from .BTF_ids .BTF.ids (following .BTF.ext example)
  - add .BTF.ids section info into btf.rst [John]
  - updated over letter with more details [John]

Also available at:
  https://git.kernel.org/pub/scm/linux/kernel/git/jolsa/perf.git
  bpf/d_path

thanks,
jirka


---

Have you considered splitting this series into two? One with BTF ID
resolution and corresponding patches. I'm pretty confident in that one
and it seems ready (with some minor selftest changes). Then,
separately, d_path and that sub-struct address logic. That one depends
on the first one, but shouldn't really block BTF ID resolution from
going in sooner.

Jiri Olsa (14):
      bpf: Add resolve_btfids tool to resolve BTF IDs in ELF object
      bpf: Compile resolve_btfids tool at kernel compilation start
      bpf: Add BTF_ID_LIST/BTF_ID macros
      bpf: Resolve BTF IDs in vmlinux image
      bpf: Remove btf_id helpers resolving
      bpf: Use BTF_ID to resolve bpf_ctx_convert struct
      bpf: Allow nested BTF object to be refferenced by BTF object + offset
      bpf: Add BTF_SET_START/END macros
      bpf: Add info about .BTF.ids section to btf.rst
      bpf: Add d_path helper
      tools headers: Adopt verbatim copy of btf_ids.h from kernel sources
      selftests/bpf: Add verifier test for d_path helper
      selftests/bpf: Add test for d_path helper
      selftests/bpf: Add test for resolve_btfids

[...]