Re: pahole: soliciting naming suggestion for struct btf rename

[Arnaldo Carvalho de Melo <acme@kernel.org>]

Em Fri, Feb 15, 2019 at 09:25:48AM -0800, Andrii Nakryiko escreveu:
> On Fri, Feb 15, 2019 at 9:15 AM Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com> wrote:
> > Em Thu, Feb 14, 2019 at 08:37:51PM -0800, Andrii Nakryiko escreveu:
> > > On Thu, Feb 14, 2019 at 6:01 AM Arnaldo Carvalho de Melo <arnaldo.melo@gmail.com> wrote:
> > > Yes, libbpf's struct btf is immutable read-only view of .BTF section
> > > that can come from either file or kernel. When I'll be adding BTF
> > > writing (encoding) API, it probably will be done using something
> > > similar to pahole's struct btf, that supports dynamic growth of types

> > Ok, I noticed that libbpf's btf__new() does load things into the kernel,
> > perhaps we should have it not do that and instead have some other method
> > for asking it to send the data to kernel, i.e.:

> >         struct btf *btf = btf__new();
> >         int err = btf__load_to_kernel(btf, data, size);

> > Or have multiple constructors, each specifying what it actually does,
> > i.e.:

> > To get a btf data + size and insert it into the kernel, getting its fd,
> > etc:

> >         struct btf *btf = btf__new_to_kernel(data, size);

> > For asking for BTF info that is already in the kernel to be obtained for
> > tooling to parse maps in running bpf programs:

> >         struct btf *btf = btf__new_from_kernel(fd);

> > And for the pahole case it would be:

> >         struct btf *btf = btf__new_from_elf(file-with-BTF-ELF-section)

> > that would then be used to do the encoding, etc.

> We already did that a couple of days ago, that code wasn't yet
> mirrored into github.com/libbpf/libbpf until yesterday (it was merged
> this morning). We now have btf__new(data, size) that just constructs
> in-memory BTF struct with index for types. And we have
> btf__load(struct btf* btf) that can load that into kernel.

cool
 
> We already have equivalent of btf__new_from_kernel(fd) -- btf__get_from_id(fd).

cool, if it allocates space for sizeof(*btf) and returns this newly
allocated object, then please consider renaming it to btf__new_from_id(fd).

> Adding something akin to btf__new_from_elf() might be a good idea as
> well, for completeness.

Its nice to be on the same page :-)

<SNIP>
 
> > > > @@ -645,7 +636,7 @@ static int btf__write_elf(struct btf *btf)
> > > >                         llvm_objcopy = "llvm-objcopy";
> > > >
> > > >                 /* Use objcopy to add a .BTF section */
> > > > -               snprintf(tmp_fn, sizeof(tmp_fn), "%s.btf", btf->filename);
> > > > +               snprintf(tmp_fn, sizeof(tmp_fn), "%s.btfe", btfe->filename);
> > >
> > > This is probably unintentional change, though not a problem per se.
> >
> > Eagle eyes, I'll fix that.
 
> :)

- Arnaldo