Expose target_obj_id and target_btf_id fields in TracingLinkInfo

[frobware]

Expose target_obj_id and target_btf_id fields in TracingLinkInfo to provide access to BPF tracing link information without requiring additional syscalls.

These fields are already available in the kernel's bpf_link_info struct and are exposed by bpftool, but were being ignored by libbpf-rs. This forces applications to make additional syscalls via bpf_obj_get_info_by_fd() to retrieve information that was already available from the initial query.

Changes

• libbpf-rs/src/query.rs: Add target_obj_id and target_btf_id fields to TracingLinkInfo struct
• examples/bpf_query/src/main.rs: Enhanced to demonstrate the new fields for tracing links
• libbpf-rs/CHANGELOG.md: Document the enhancement

Fields Added

• target_obj_id: prog_id for PROG_EXT links, otherwise BTF object ID
• target_btf_id: BTF type ID inside the target object

Example Output

After this change, the bpf_query example shows:

$ sudo ./target/debug/bpf_query link
id=   6 prog_id=1437 type=tracing
    attach_type=LsmMac target_obj_id=1 target_btf_id=59022

This correlates with bpftool output:

$ sudo bpftool link show id 6
6: tracing  prog 1437
        prog_type lsm  attach_type lsm_mac
        target_obj_id 1  target_btf_id 59022

Benefits

• Performance: Eliminates additional syscalls for BPF introspection tools
• Consistency: Follows existing pattern of exposing all available kernel fields
• Compatibility: only adds new fields

[d-e-s-o]

Looks mostly good to me, thanks. Left two comments. Also, can you please combine the CHANGELOG commit into the one adding the fields? No need to separate.

[d-e-s-o]

Please move into a new Unreleased section. See af0910e#diff-4c0b9d3ba9467bbce23979f2823a77684818168c500364d9652b70eac9dfe1f9

[frobware]

Done in https://github.com/libbpf/libbpf-rs/compare/bae77fc949a8f468d5b57749882e28f6f77c1dc1..c4b8e11dc83fb80cf4ba8d3c8cf98ad6cad17d78.