Short-circuits `CACHE` to true if the field is non-zero.
This saves from executing the probing logic since the logic essentially
checks if the field can process (or doesn't error) non-zero value.
Cached probed for ProgramInfo fields instead of exposing it through
global FEATURE. Probing occurs on cache miss, which happens when first
accessing the field, *and* if the field is 0.
Change FromRawTracepointArgs::arg to return T rather than *const T which
seems to have been returning a dangling pointer.
Arguably this is not strictly necessary; edition 2024 seems to be
focused on increased strictness around unsafe code which doesn't unlock
new functionality for our users. That said, this work revealed an
apparent bug (see above) that we wouldn't otherwise catch due to
allow-by-default lints.
Per man 2 bpf:
> RETURN VALUE
> For a successful call, the return value depends on the operation:
>
> BPF_MAP_CREATE
> The new file descriptor associated with the eBPF map.
>
> BPF_PROG_LOAD
> The new file descriptor associated with the eBPF program.
>
> All other commands
> Zero.
>
> On error, -1 is returned, and errno is set to indicate the error.
Bake this into our syscalls so we stop using `_` so much which can hide
information loss.
Purpose of this commit is to add detections for whether a field is
available in `ProgramInfo`.
- For `program_type()`, we return the new enum `ProgramType` instead of
the integer representation.
- For fields that we know cannot be zero, we return `Option<NonZero*>`
type.
- For `name_as_str()`, it now also uses the feature probe `bpf_name()`
to detect if field is available or not.
- Two additional feature probes are added for the fields:
- `prog_info_map_ids()` probe -> `map_ids()` field
- `prog_info_gpl_compatible()` probe -> `gpl_compatible()` field
With the `prog_info_map_ids()` probe, the previous implementation that
I had for `bpf_prog_get_info_by_fd()` is shortened to use the probe
instead of having to make 2 potential syscalls.
The `test_loaded_at()` test is also moved into info tests since it is
better related to the info tests.
`aya::programs::Programs::prog_type(&self)` now returns `ProgramType`
instead of the generated FFI from aya-obj.
Also previously, `loaded_programs()` could be accessed either through
`aya` or `aya::programs`. To avoid confusion and duplicate export of
the item, the function should now only be exposed through
`aya::programs`.
