On Sun, Feb 20, 2022 at 07:17:59PM +0530, Kumar Kartikeya Dwivedi wrote:
> In next few patches, we need a helper that searches all kernel BTFs
> (vmlinux and module BTFs), and finds the type denoted by 'name' and
> 'kind'. Turns out bpf_btf_find_by_name_kind already does the same thing,
> but it instead returns a BTF ID and optionally fd (if module BTF). This
> is used for relocating ksyms in BPF loader code (bpftool gen skel -L).
>
> We extract the core code out into a new helper
> btf_find_by_name_kind_all, which returns the BTF ID and BTF pointer in
> an out parameter. The reference for the returned BTF pointer is only
> bumped if it is a module BTF, this needs to be kept in mind when using
> this helper.
>
> Hence, the user must release the BTF reference iff btf_is_module is
> true, otherwise transfer the ownership to e.g. an fd.
>
> In case of the helper, the fd is only allocated for module BTFs, so no
> extra handling for btf_vmlinux case is required.
>
> Signed-off-by: Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>
> ---
> kernel/bpf/btf.c | 47 +++++++++++++++++++++++++++++++----------------
> 1 file changed, 31 insertions(+), 16 deletions(-)
>
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index 2c4c5dbe2abe..3645d8c14a18 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -6545,16 +6545,10 @@ static struct btf *btf_get_module_btf(const struct module *module)
> return btf;
> }
>
> -BPF_CALL_4(bpf_btf_find_by_name_kind, char *, name, int, name_sz, u32, kind, int, flags)
> +static s32 btf_find_by_name_kind_all(const char *name, u32 kind, struct btf **btfp)
The name is getting too long.
How about bpf_find_btf_id() ?
> {
> struct btf *btf;
> - long ret;
> -
> - if (flags)
> - return -EINVAL;
> -
> - if (name_sz <= 1 || name[name_sz - 1])
> - return -EINVAL;
> + s32 ret;
>
> btf = bpf_get_btf_vmlinux();
> if (IS_ERR(btf))
> @@ -6580,19 +6574,40 @@ BPF_CALL_4(bpf_btf_find_by_name_kind, char *, name, int, name_sz, u32, kind, int
> spin_unlock_bh(&btf_idr_lock);
> ret = btf_find_by_name_kind(mod_btf, name, kind);
> if (ret > 0) {
> - int btf_obj_fd;
> -
> - btf_obj_fd = __btf_new_fd(mod_btf);
> - if (btf_obj_fd < 0) {
> - btf_put(mod_btf);
> - return btf_obj_fd;
> - }
> - return ret | (((u64)btf_obj_fd) << 32);
> + *btfp = mod_btf;
> + return ret;
> }
> spin_lock_bh(&btf_idr_lock);
> btf_put(mod_btf);
> }
> spin_unlock_bh(&btf_idr_lock);
> + } else {
> + *btfp = btf;
> + }
Since we're refactoring let's drop the indent.
How about
if (ret > 0) {
*btfp = btf;
return ret;
}
idr_for_each_entry().
and move the func right after btf_find_by_name_kind(),
so that later patch doesn't need to do:
static s32 bpf_find_btf_id();
Eventually this helper might become global with this name.
Also may be do btf_get() for vmlinux_btf too?
In case it reduces 'if (btf_is_module())' checks.
