On Mon, Jul 31, 2023 at 12:30 AM Masami Hiramatsu (Google)
<mhiramat@xxxxxxxxxx> wrote:
>
> From: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
>
> Add btf_find_struct_member() API to search a member of a given data structure
> or union from the member's name.
>
> Signed-off-by: Masami Hiramatsu (Google) <mhiramat@xxxxxxxxxx>
> Reviewed-by: Alan Maguire <alan.maguire@xxxxxxxxxx>
> ---
> Changes in v3:
> - Remove simple input check.
> - Fix unneeded IS_ERR_OR_NULL() check for btf_type_by_id().
> - Move the code next to btf_get_func_param().
> - Use for_each_member() macro instead of for-loop.
> - Use btf_type_skip_modifiers() instead of btf_type_by_id().
> Changes in v4:
> - Use a stack for searching in anonymous members instead of nested call.
> ---
> include/linux/btf.h | 3 +++
> kernel/bpf/btf.c | 40 ++++++++++++++++++++++++++++++++++++++++
> 2 files changed, 43 insertions(+)
>
> diff --git a/include/linux/btf.h b/include/linux/btf.h
> index 20e3a07eef8f..4b10d57ceee0 100644
> --- a/include/linux/btf.h
> +++ b/include/linux/btf.h
> @@ -226,6 +226,9 @@ const struct btf_type *btf_find_func_proto(const char *func_name,
> struct btf **btf_p);
> const struct btf_param *btf_get_func_param(const struct btf_type *func_proto,
> s32 *nr);
> +const struct btf_member *btf_find_struct_member(struct btf *btf,
> + const struct btf_type *type,
> + const char *member_name);
>
> #define for_each_member(i, struct_type, member) \
> for (i = 0, member = btf_type_member(struct_type); \
> diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c
> index f7b25c615269..8d81a4ffa67b 100644
> --- a/kernel/bpf/btf.c
> +++ b/kernel/bpf/btf.c
> @@ -958,6 +958,46 @@ const struct btf_param *btf_get_func_param(const struct btf_type *func_proto, s3
> return NULL;
> }
>
> +#define BTF_ANON_STACK_MAX 16
> +
> +/*
> + * Find a member of data structure/union by name and return it.
> + * Return NULL if not found, or -EINVAL if parameter is invalid.
> + */
> +const struct btf_member *btf_find_struct_member(struct btf *btf,
> + const struct btf_type *type,
> + const char *member_name)
> +{
> + const struct btf_type *anon_stack[BTF_ANON_STACK_MAX];
> + const struct btf_member *member;
> + const char *name;
> + int i, top = 0;
> +
> +retry:
> + if (!btf_type_is_struct(type))
> + return ERR_PTR(-EINVAL);
> +
> + for_each_member(i, type, member) {
> + if (!member->name_off) {
> + /* Anonymous union/struct: push it for later use */
> + type = btf_type_skip_modifiers(btf, member->type, NULL);
> + if (type && top < BTF_ANON_STACK_MAX)
> + anon_stack[top++] = type;
> + } else {
> + name = btf_name_by_offset(btf, member->name_off);
> + if (name && !strcmp(member_name, name))
> + return member;
> + }
> + }
> + if (top > 0) {
> + /* Pop from the anonymous stack and retry */
> + type = anon_stack[--top];
> + goto retry;
> + }
Looks good, but I don't see a test case for this.
The logic is a bit tricky. I'd like to have a selftest that covers it.
You probably need to drop Alan's reviewed-by, since the patch is quite
different from the time he reviewed it.
Assuming that is addressed. How do we merge the series?
The first 3 patches have serious conflicts with bpf trees.
Maybe send the first 3 with extra selftest for above recursion
targeting bpf-next then we can have a merge commit that Steven can pull
into tracing?
Or if we can have acks for patches 4-9 we can pull the whole set into bpf-next.
