On 6/7/23 4:55 AM, Eduard Zingerman wrote:
On Tue, 2023-06-06 at 13:30 +0200, Toke Høiland-Jørgensen wrote:
[...]
As for bumping the version number, I don't think it's a good idea to
deliberately break compatibility this way unless it's absolutely
necessary. With "absolutely necessary" meaning "things will break in
subtle ways in any case, so it's better to make the breakage obvious".
But it libbpf is not checking the version field anyway, that becomes
kind of a moot point, as bumping it doesn't really gain us anything,
then...
It seems to me that in terms of backward compatibility, the ability to
specify the size for each kind entry is more valuable than the
capability to add new BTF kinds:
- The former allows for extending kind records in
a backward-compatible manner, such as adding a function address to
BTF_KIND_FUNC.
Eduard, the new proposal is to add new kind, e.g., BTF_KIND_KFUNC, which
will have an 'address' field. BTF_KIND_KFUNC is for kernel functions.
So we will not have size compatibility issue for BTF_KIND_FUNC.
- The latter is much more fragile. Types refer to each other,
compatibility is already lost once a new "unknown" tag is introduced
in a type chain.
However, changing the size of existing BTF kinds is itself a
backward-incompatible change. Therefore, a version bump may be
warranted in this regard.
